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FOR THE PEOPLE

FOR EDVCATION
FOR SCIENCE

LIBRARY

OF

THE AMERICAN MUSEUM

OF

NATURAL HISTORY

THE EVOLUTION
AND DISTRIBUTION OF FISHES

^9-

THE EVOLUTION

AND DISTRIBUTION OF

FISHES

By

c

y

JOHN MUIRHEAD MACFARLANE, D. Sc, L.L. D.

Emeritus Professor of Botany ;

University Carnegie Foundationer;

Late Director of the Botanic Garden;

University of Pennsylvania.

^ew Pork

THE MACMILLAN COMPANY

1923

Copyright, 1923

by

J. M. Macfarlane

All Rights Reserved

Printed by

Enterprise Publishing Company

Burlington, N. J., U. S. A.

With Pleasure

The Author dedicates this volume

to

Mrs. William West Frazier, Jr.

as a sincere token of appreciation

for her sympathetic interest

in his aims and studies.

PREFACE

In 19 1 8 the writer published a volume that was entitled
"The Causes and Course of Organic Evolution." A section
of it was devoted to an inquiry into the environal relation
of plants and animals, as determining largely their distribu-
tion in time and space. The conclusion was then reached,
that organisms evolved first in freshwater areas, and only
by degrees spread into marine surroundings.

During his inquiries the author gradually concluded
that fishes might form the most important biological group
by which to test the value of such a conclusion. For in the
volume named he presented short details of their past and
present history, which seemed to indicate that they at
first evolved amid freshwater surroundings. Field studies
also made by the writer during his earlier scientific career
and subsequently, strongly pointed in like direction. But
some details that either weakened the position, or that
claimed further investigation, accumulated amid the abund-
ant evidence that proved to be favorable. The writer there-
fore resolved to make as thorough a comparison as possible
of the groups of fishes, and even of specific genera amongst
these.

The outcome is seen in part in the present volume,
which represents the almost continuous labors of the past
six years. As the author pursued his detailed researches,
some originally puzzling conditions gradually began to
have a definite meaning attached to them. Thus the pres-
ence of abundant fossilized fish remains in zones of cannel
coal, and their absence from ordinary coal strata; the like
occurrence of freshwater fishes and of related organisms
ecologically in the oil shales of the Edinburgh Coal Field
that the writer studied for years in his earlier career; the
peculiar character, the chemical composition, and the fos-
silized fish remains, of the marls that he studied in mature
years from New Jersey to Florida, all had welcome light
thrown on them, at the same time that the evolutionary his-
tory of fishes unfolded in its manifold ramifications.

So as the results of observation and of study accumu-
lated, it became evident that two related but distinct vol-
umes were needed, in order that the conclusions reached
might be placed properly before the scientific world. That
now presented was written in 1920-21, and finished in Au-
gust of the latter year. The other, which bears title :
"Fishes the Source of Petroleum," was largely written from
the early part of 192 1 onward, and was finished in Decem-
ber of 1922. Any discriminating reader of the two volumes
will readily perceive that some such history attaches to them.

In preparing both volumes the writer has endeavored
to quote the exact words of authors whose observations
he has referred to. The reader therefore can now share
with the writer the pleasure of examining original, and so
ever-fresh, statements that bear on questions at issue.

While the writer has spent years in study of rock forma-
tions and their included organic remains, it is of necessity
true that many of his statements have been derived from
examination of the published investigations of others. Such
also is true of the abundant zoological results here pre-
sented. But for any defects that may be shown in this
presentation, the writer desires to be alone responsible. If
therefore conclusions are here reached that will advance
scientific truth, such deserve to be conserved; should some
prove to be incorrect, they can readily be discarded. For
all scientific 'advance has shown that Truth alone will en-
dure, error and misstatement will fade away.

Special and grateful acknowledgment is now made of
the invaluable aid furnished by the writings, and in some
cases by the illustrations, of A. S. Woodward; of his early
teachers and friendly helpers Sir A. Geikie and Dr. R. H.
Traquair; of his university predecessor or colleague, Pro-
fessors Leidy and Cope. In dedication of this volume to
a lady who has ever striven to aid and advance scientific
progress, the author pays a small but deserved tribute.
The printers and publishers of it have shown that considera-
tion and regard, which ensure that it can worthily see the
light.

Philadelphia, April, 1923.

CONTENTS

PAGE

Chapter I.
Introduction i

Chapter II.
Geological Conditions in relation to the Evolution of

Fishes 23

Chapter III.
The Evolution of Fishes from Invertebrates 60

Chapter IV.
The Physical and Biological Environment of Fishes

in Silurian and Devonian Times 96

Chapter V.
The Physical and Biological Environment of Fishes
in Carboniferous and Permian Times 137

Chapter VI.
The Physical and Biological Environment of Fishes

during the Triassic- Jurassic Period 172

Chapter VII.
The Physical and Biological Environment of Fishes

during the Cretaceous Period 208

Chapter VIII.
The Physical and Biological Environment of Fishes

from Eocene to Recent Times 231

Chapter IX.
Primitive Fishes in Time and Space 256

Chapter X.
The Dipneusti and Crossopterygii in Time and Space 293

Chapter XL
The Chondrostei and Holostei in Time and Space. . . 316

Chapter XII.
The Soft-finned Teleostei in Time and Space 346

Chapter XIII.

The Spine-finned Teleostei in Time and Space 372

Chapter XIV.

Past Geographic and Geologic Conditions in Relation

to the Distribution of Fishes 402

Chapter XV.
Fishes in Relation to a South Atlantic Continent 431

Chapter XVI.
A Review of the Tanganyilca Problem 463

Chapter XVII.

The Geographic and Geologic Relations of the More

Primitive Fishes 483

Chapter XVIII.

Synoptic Review of Previous Chapters 503

References to Literature 534

Index 542

THE EVOLUTION
AND DISTRIBUTION OF FISHES

CHAPTER I

Introduction

It has been a generally accepted dictum with zoologists
during the past hundred years, and has been even more
emphasized during the past twenty, that animal life in
general and not least the great group of fishes originated
amid marine surroundings, and only gradually spread to-
ward a freshwater environment. Were one to adduce evi-
dence for this it might be said to include the views set
forth in every important manual and textbook on zoology
and palaeozoology, as well as in the well-known special
treatises and research volumes that deal with recent as
well as fossil fishes. And yet against such a conclusion
there existed many weighty observations and field studies,
brought forward by the very authors of the marine idea.

The writer spent much available time during several
years of his student and earlier teaching days m investi-
gating the fossil flora and fauna of the Edinburgh region,
and also the stratigraphic relation of these. The area
covered included extensive developments of Lower Car-
boniferous or Calciferous sandstone rocks that extend for
miles westward from Edinburgh as well as across the
Firth of Forth into a large part of Fifeshire. It also
included the higher group of rocks known as the Carbon-
iferous Limestone that stretches in extensive beds and as
a great trough, from some miles east of Edinburgh across
into Fifeshire. Above this were the Millstone Grit and
the True Coal Measures, both widely developed on either
side of the Firth. Dura Den, of classic Old Red Sandstone
fame, adjoined the writer's ancestral territory, while the
Silurian beds of the Pentland hills came in for a share
of attention.

2 Evolution and Distribution of Fishes

Throughout all of these strata, with the exception only
of the Carboniferous Limestone series, abundant fossil
plant remains often occurred side by side with entire fossil
fishes, or with their jaws, teeth, scales and spines. Such
remains again were at times associated with a stippled
and shining body that on reference to the skilled palae-
ontologist Traquair was identified as part of a carbon-
iferous eurypterid. Occasional thin beds of what were
identified as freshwater carboniferous molluscs at times
interrupted the plant and fish bearing strata, while the
now celebrated freshwater limestones of Burdie House, and
of Camps near Mid Calder, revealed remains of ferns,
lepidodendra, calamites, and fishes, surrounded by myriads
of freshwater entomostracans, mainly Leperditia scoto-
burdiegalensis.

Here then seemed to be an enormous accumulation of
non-marine strata, that at times was constituted in places by
beds of coal from one or two inches to five feet in thick-
ness. In striking contrast to all of this were the rocks
and enclosed fossils that made up the main masses of the
Carboniferous Limestone system, on top of which the
writer was born and lived through his preuniversity years.
These often literally teemed with a complex of fossils that
proclaimed a very different and a typically marine life.
Broken remains of Productus, Spirifer, Encrinus, Euom-
phalus, and other equally characteristic marine organisms
at times almost made up the limestone basis in which the
more entire calcareous tests were imbedded. But amongst
all of these marine beds, over wide miles of country
studied, the writer only rarely found a genuine fish remain.

More arresting and puzzling still, according to the then
accepted views, was the occasional Interbedding amongst
the Carboniferous Limestone rocks of an ironstone stratum
that enclosed just such plants, fishes and eurypterlds as
characterized the Calclferous rocks below. Their fossil-
ized remains usually occurred In ironstone or In ferruginous
shale, that Indicated chemical interaction between organ-
Isms and dissolved Iron salts, the latter of which had pre-
cipitated from the surrounding waters. With glee Tra-
quair at times welcomed such fish specimens when brought

Introduction 3

to him for Identification, or displayed others that he had
gathered and on which he was then (i 876-1 882) pub-
lishing.

The Impression was, therefore, almost unwillingly
forced in on the writer's mind, now fully forty years ago,
that during the great Carboniferous epoch a practically
continuous deposit of freshwater strata with typical plant
and fish enclosures gave rise to the foundation beds or
Calclferous Sandstone series of that system; that then an
extensive though not deep submergence of land occurred
under the sea, during which the Carboniferous Limestone
was formed as a great marine deposit. Even then however
occasional elevation for a longer or shorter time permitted
the development of a nearby land flora and Invasion again
of teeming freshwater fishes In lakes or swamps of that per-
iod. These however showed no trace of existence In marine
strata. Finally, during deposit of the Coal Measures,
freshwater fishes that were very different in type from those
of the lower rocks, were met with In Ironstone in shale,
or in sandstone strata that alternated with and often shaded
into coal beds.

The mental picture thus gradually formed through a
period of fully five years — namely from 1876 to 1881 —
seemed antagonistic to the tacit or openly expressed views of
many palaeontologists and zoologists. Very slowly through
succeeding decades a correct explanation began to dawn,
and this was outlined recently In the volume that the
present writer has entitled "The Causes and Course of
Organic Evolution." Shortly stated, and founding on facts
presented In Chapters 11, 12, 14, and 18 of that work, he
would claim that all organic life evolved In freshwater
and even most primitively in thermal or subthermal areas
akin to those of the Yellowstone, the New Zealand, the
Austrian, the Icelandic and like regions of to-day. This also
took place, he considers, In early proterozoic, protoblotic
or archean time. Gradually new and ever more complex
forms evolved which continued to Inhabit freshwaters.
But from such freshwater environment successive organ-
ismal Invasions of the sea first, and of the land at a later
period, started the main groups of marine plants and ani-

4 Evolution and Distribution of Fishes

mals as well as the land types. The marine environment
once reached, there were presented wide and continuous
fields of activity in migration, in feeding, in escape from
foes, in reproduction, and in rearing of the young. Varied
and changing environal stimuli steadily produced new and
varied forms that became increasingly adapted to marine
life, but seldom indeed showed capacity for readaptation
to freshwater, not to say land existence.

In an address before the Academy of Natural Sciences
of Philadelphia in 19 12, the writer explained the appli-
cation of these principles to the leading groups of animals,
and an abstract of this address was published later by Dr.
A. W. Miller in his "Report on the Progress of Botany"
in "Proceedings of the 36th Annual Meeting, Pennsylvania
Pharmaceutical Association" (19 13). Such were his first
published statements regarding the origin of the important
groups of animals. In applying these principles to fishes
in the volume already quoted (p. 403) the writer expressed
himself as follows: "We would shortly sum up our con-
clusions by saying that the Cyclostomata were probably, as
they still are in part, of freshwater origin; that the Se-
lachii are and have been through long epochs nearly all
evolved as marine forms; that the Polypteridae are and
probably have been freshwater in habitat and history; that
the Dipneustei are similar to the last; that the Chondrostei
or spoonbill and sturgeon series agree with the two last
except that some of the sturgeons pass into the sea to feed
and return inland to spawn; that the Holostei are now
wholly freshwater; that of the thirteen suborders of the
Teleostei given by Boulenger, the first or Malacopterygii
are almost wholly freshwater, the third or Symbranchii are
mainly fresh — more rarely brackish water inhabitants, the
fourth or Apodes — that includes the eels — are rarely fresh-
water, usually marine and breeding there at considerable
depths, the fifth or Haplomi — that includes the common
pike — are largely freshwater though a fair number live
and even breed in the sea, and the remaining nine (Heter-
omi; Catosteomi, etc.) are almost wholly marine with rare-
ly freshwater inclusive genera.

Introduction 5

"But a comparative review of the number of freshwater
and marine genera of the present day, in the light of their
known first appearance in geologic time, brings out some
rather remarkable results. Thus, of the entire group of
the Gnathostomata or toothed fishes, 453 living genera
are purely freshwater in their life history, and 902 genera
are marine, with occasional freshwater representatives.
But when such statistics are compared with the geological
record, another and different relation Is revealed. The old-
est known groups of the true fishes are the Crossopterygii,
the Dipneustei, and the Chondrostel, representatives of
all of which have been found in the lower Devonian. All
of these are freshwater forms at the present day, and many
if not all of the fossil forms likewise were. But as these at-
tained to the greatest climax of their development In inland
seas, In lacustrine and in fluviatlle situations, the group of
the Selachii probably evolved from the primitive acantho-
deans, took to a marine life, and soon became an increasing-
ly powerful type of fish up to the period of the carboniferous
epoch or even later. Their aggressive and voracious ten-
dencies, their often lithe movements, and their inclination
to feed on dead as well as living animal matter, seem to have
enabled them to contend successfully with the giant repre-
sentatives of the cephalopod molluscs that at that time
largely held the seas. But the highest or teleostome fishes
gradually evolved from the Permian period onward In ever
Increasing numbers. It Is a striking fact however that, if
we compare the number of living genera of fishes whose
ancestry dates from the period of the Cretaceous or further
back, 320 living genera are freshwater, and 155 are marine.
Only during the period from the Cretaceous and especially
from the beginning of the Eocene onward do the teleo-
stean fishes attain that enormous marine development
which now characterizes them; so that, while 133 genera of
recently evolved living teleosteans are freshwater, 747
genera are marine. This remarkable development seems
to have been correlated with a gradual dying out alike of
the dominant groups of cephalopod molluscs and of sela-
chean fishes. So, when we sum up all of the living genera
of gnathostome fishes, and find that 453 are freshwater

6 Evolution and Distribution of Fishes

and 902 are marine, this by no means represents the prim-
itive distributional relation.

"We would therefore consider that all palaeontological,
structural, and geographical evidence strongly favors the
view that the primitive fishes have had a freshwater origin,
and that derivative marine forms have evolved from these,
which in the case of the anciently derived selacheans, and
of the recent teleosteans, reached each to a high climax of
species diversity, the former during the Cretaceous period,
the latter in our own day."

If such conclusions are in harmony with the phylogeny
and gradual distribution of fishes over freshwater and salt-
water areas it should be highly probable that its correctness
can be demonstrated by an appeal to the palaeontological
record. Further, if that record is sufficiently complete, it
should enable us to determine with fair accuracy the ap-
proximate period when the main groups and even the
smaller families of fishes migrated from a freshwater to
a marine environment or vice versa. As a result an evolu-
tionary sequence and exactness could thereby be obtained
that would be in helpful contrast to the vague and un-
certain record of the past.

In now selecting the group of fishes for detailed treat-
ment the writer has been guided by several considerations.
First, it has been generally accepted as the group that con-
nects the invertebrates with the more evolved vertebrates.
Second, it shows several very distinct living divisions that
can nevertheless be traced back through the greater extent
of the palaeontological record to forms that strongly
suggest community of origin and structure ; Third, from
its environal relations, and so from causes that will be
fully discussed later, the group is one that is surprisingly
well represented from later Silurian times up to the present
day. Fourth, in spite of the great amount relatively of
soft tissue that makes up each individual, the early for-
mation, from at least Silurian times onward, of external
scales and later of a resisting bony framework, ensured
preservation of the remains in an exceptionally favorable
manner. Fifth, owing to rare but remarkable combina-
tions of geological conditions, that are fully discussed later

Introduction 7

on, the above parts are at times encountered in enormous
quantity and in a beautiful state of preservation. Sixth,
the group has furnished so large a share of human food
that it has received much careful and detailed attention.

Such combined conditions are possessed by few if any
other divisions of animals. But the writer might add that
he hopes soon to publish data that will serve equally well
to elucidate the past and present history of the Crustacea.
Still later it may be possible to treat the Mollusca in
a similar manner, thougih the effort promises to be a
more extended one. But should some student of this last
great and diverse assemblage be inclined to undertake the
work alike from the embryological, the morphological,
the ecological, the taxonomic and palaeontological side, the
results will unquestionably be of highest value.

In undertaking such a study as the present, the writer
is fully conscious of his own limitations and shortcomings,
but would plead in fullest extenuation that having reached
certain published conclusions it is incumbent on him to
verify or to disprove the statements already made. The
field is a wide one, the evidences must be drawn from many
and diverse sources of human knowledge, the conclusions
reached must be fortified by abundant and exact obser-
vations, such conclusions also must fit in with like obser-
vations made for other groups of animals than the fishes,
as well as for plants. Finally the facts obtained from
study of fossil forms must be correlated with, and must
lead up to, a correct interpretation of the data already
gathered as to living fishes.

So in the immediately succeeding chapters consideration
is given to such general questions as the changes of the
earth before and during the period of the evolution of
fishes; the possible relation of recent to fossil fishes; the
environal conditions by which evolving fishes were sur-
rounded; the invertebrate predecessors and ancestors of
fishes; also the succession of forms observed during
successive epochs. Only thus is it possible to obtain a fairly
concrete and accurate picture of the group as a whole.
Such treatment also forms a fitting introduction to still
later chapters, which deal with the great subdivisions of

8 Evolution and Distribution of Fishes

the group, alike in their morphological aspects and as
yielding confirmatory and detailed verification of the prin-
ciples already laid down In the earlier volume by the author.

In the remainder of this chapter we may now consider
the fundamental evolutionary causes which effected the de-
velopment of fishes from simpler types; the mode of opera-
tion of these causes; and the relative Importance of each
causal agent alongside others that operated.

As more fully set forth In the work already referred
to, the writer would regard It as a great and fundamental
law that all organisms have evolved — not through the
agency of matter or chemical atoms as ordinarily under-
stood — but from the continuous activity and increasing
condensation of energy. This universally present energy,
activating and building up atoms Into organic molecules,
shows successive condensation phases that we designate,
according to their wave-length and other physical proper-
ties, the thermic, lumic, chemic and electric states of energy-
motion. These in the order named, and when acting on
simple chemical atoms, gradually build up or link together
those inorganic compounds that pass from bivalent to tri-
valent and thence to quartivalent compounds. The matter
or chemical atoms thus acted on are in themselves inert,
passive, dead; but according to the condensation quality
and phase of the energy applied they assume those con-
ditions of atomic linkage and those physical characters that
determine the different types of molecules.

But in passing from the Inorganic to the organic, the
writer has suggested (7:73-96)* the further condensation
of electric energy into that state of energy-action which
he has named the duplo-electric, and which he considers to
be specially concerned In elaboration of those colloid mole-
cules that form the necessary basis of all organic existence.
The colloid states of many Inorganic bodies are now well
known, since the first description of them by Graham,
now little more than a half century since. The colloid
states of silicon, sulphur. Iron, platinum, silver, gold and
others, are now well recognized. In all of these, as in

*In all references to literature, the first and italicized number indicates the author
and work in question as given in "References to Literature" on pp. 534-542, the second
number indicates the page.

Introduction" 9

all organic tissues, water is an essential constituent of each
molecule, and gives to combined molecular masses a degree
of plasticity, adaptability, and gradual response to envir-
onal changes that at once suggest and foreshadow organic
molecular linkages.

But for the upbuilding of complex organic molecules the
writer considers that gradually, by action and reaction be-
tween increasingly complex colloid molecules, a more con-
densed form of energy than the duplo-electric developed,
which he has named the biotic. This arose as environal
terrestrial factors became appropriate to, and stimulating
for its development.

Definite heat of, and heat-radiations from, the earth;
definite chemic actions and reactions, that resulted in link-
ages into complex mineralogic molecules; definite currents
of electric energy through definite bodies of varied but
varying conductivity or resistance; definite formations of
mixed and complex colloid bodies from dissolved minerals;
these and many like conditions that must have evolved as
the earth itself evolved as a steadily cooling mass, might
and probably did favor biotic energy-condensation.

This energy, conducted only through complex colloid
molecular masses, stimulated the formation of many of the
simpler and ultimately highly complex bodies like proto-
plasm of the organic realm, which then became its special
vehicle or conductor. In relation to environment such high-
ly organized energy-matter complexes showed exactly those
responses that were more or less characteristic of all bodies,
but specially of colloid ones, as Le Bon and S. Le Due have
indicated (5;^;passim), and as the present author has pre-
sented in his work (1:31). So the five great physiological
activities of irritability or capacity for molecular response
to environment, nutrition or the absorption and dispos'mg
of new particles to replace those removed, respiration or
the removal of superfluous effete particles — a phenomenon
feebly shown by some inorganic colloid bodies, growth or
increase in molecular complexity or size or in both, and
reproduction or the throwing off of a portion of the whole
that would serve to multiply and perpetuate the type; all
became stamped on primitive organic bodies as an evolved

lo Evolution and Distribution of Fishes

and more perfect heritage from simpler inorganic colloid
substances or bodies.

Each of these functions also might vary in activity, in
exhibition, in relation the one to the other, or to agencies
around, according to the kind and strength of environal
stimuli that the organism might be exposed to. This will
be seen to be strikingly true in the history of many groups
of fishes at various stages in their existence.

But an examination of the simplest plant and animal
organisms now living tends to show that the latter branched
off from the former as a group that gradually became
adapted to active motion, or in other words which showed
increasingly active and delicate response to environal stim-
uli; also that they came to depend more and more on the
catching and absorption of other living organic bodies, that
is they became epibiotic in their nutritive relations. Soon
however the common stock of simpler plants and of the
most primitive animals, that had branched off from them
in their higher members, became increasingly responsive
to environal stimuli, and so a still higher and more perfect
quality of energy condensed from the biotic, and such the
writer has termed the cognitic. This became associated
with a correspondingly complex exhibition of, and linkage
of, matter to form chromatin substance. And the aggre-
gation of this chromatin into a definite mass gave rise to
that highly energized body of each cell or protoplasmic
mass that we call the nucleus. So the biotic energy of each
cell protoplasm, and the more condensed cognitic energy
of each cell nucleus conferred first the vegetative (or liv-
ing) and later the actively irrito-responsive qualities on'
each organism that was made up of an aggregation of
many such cells.

Thus each organism, by activity of the protoplasm, be-
came slowly adapted to or modified for the appropriate
chemical substances that might act as food or as promoters
of respiratory change. But in virtue of the highly sensitive
and responsive chromatin substance of the nucleus, increas-
ingly active response was made to heat, light, moisture
conditions, gravity and other environal exhibitions of
energy.

Introduction i i

A stage however was evidently reached in the history
of actively motile animals when even more rapid, corre-
lated and condensed perception not of one but of several
simultaneously acting environal stimuli, and equally rapid
combination of these into a single direct response, became
necessary in the struggle for existence. Accordingly the
writer has suggested the slow evolution of that still more
condensed exhibition of energy, the cogitic, that became
correlated with and conducted by a correspondingly con-
densed linkage of molecules to constitute the neuratin or
granular network substance of nerve cells.

This stage having been reached, further evolutionary
progress up to the nemerteans and thence to fishes, con-
sisted in increasing aggregation of nerve cells to form
ganglionic masses, and ultimately in formation of the cen-
tralized brain system with its nerve fibres and its peripheral
sensory, motor and inhibitory nerve cells. But as is strik-
ingly demonstrated both by nemerteans and fishes, though
led up to by similar and simpler groups, a variety of periph-
eral sense-centers was developed to a highly perfect degree
for reception of varied environal stimuli. These became
more and more perfected as the eyes, ears, tactile skin
organs, taste organs, and nostrils of fishes. But, on the other
hand, certain sense organs, or sense centers, that were
originally present, may have undergone partial or complete
degeneration, in transition from a lower group like the
nemerteans to a higher one like the fishes. Thus can be
explained the rudimentary parietal eyes, the pituitary body,
and other structures of fishes.

But in the evolution of every structural detail five fac-
tors of prime importance are more or less actively con-
cerned, and the combined action of these five, in relation to
the energies already noted which give potency to them,
we term Pentamorphogeny, or the five form-evolving fac-
tors. These are Heredity, Environment, Proenvironment,
Selection, and Reproduction. Each is discussed in the
author's work already cited (7:174:242), but brief con-
sideration of these here with special reference to the groups
of organisms treated in the present volume, may not be
inappropriate. For they form the basic evolutionary fac-

12 Evolution and Distribution of Fishes

tors, which In varying strength, direction, time and point
of application, affect each and every organism, so as to
bring about one of three possible results. These results
may be: (a) steady and progressive, or at times rather
sudden and marked (mutational) evolution, into types that
depart more and more from the parent forms; (b) an
evenly balanced or equilibrated organic relation to sur-
rounding factors, so that through a more or less pro-
longed period of time, an organism or group of hereditarily
derived organisms may remain apparently unchanged In
structure and function; (c) a steady or rapid maladjust-
ment to environal agents, so that devolution and degen-
eration, may ensue, succeeded it may be by death of the
organism or group of organisms involved.

It follows from the above statements that the factors
of Pentamorphogeny which affect every organism, and the
results which ensue, either in evolution, equilibration, or
devolution of such organism, owe their inception to en-
vironal agents. So it is appropriate here to mention at least
some of the agents that have operated in the past either
to evolve, to continue, or to destroy the organisms specially
treated of in this volume. These environal agents are now
being more and more minutely studied under the term
ecology. And for extended consideration the reader is
referred to special books in this biological field. It is
however important to note that all of these agents represent
the action of some form of energy, whether of inorganic
or of organic origin.

Such universal environal agents as heat (thermic
energy), light (lumlc energy), chemic compounds (chemic
energy), electricity (electric energy), geotropism (gravic
energy), in their varied exhibitions, all act either together
or more or less apart, so as to affect higher Invertebrates
and fishes. Thus it has been observed that widespread
destruction of great shoals of fishes may result, if In the
case of tropical species, the temperature rather suddenly
drops, and conversely the same result may ensue if, through
rise in temperature owing to submarine volcanic action,
oceanic waters become heated above a definite optimum
for fishes of temperate seas.

Introduction 13

Sudden or slow denudation changes, alterations in the
relation and elevation or depression of land alongside rivers
and seas, the setting free into waters, of beneficial or of
deleterious food compounds, the presence or absence of par-
ticles so large or so fine as to interfere with respiratory
change, the existence of barriers that might prevent or of
passages that might promote, distribution of individuals
or species, all need consideration.

But those much more complex exhibitions of organic
energy that we group as bacterial and fungoid diseases,
or as animal parasites, may likewise operate as environal
factors of prime importance.

In the separate or joint action of the above stimuli or
energized factors, as being environal exhibitions of energy,
each organism is affected to varying extent and responds
accordingly. So by slow degree the five above named co-
operating agencies of Pentamorphogeny, viz. Heredity, En-
vironment, Proenvironment, Selection, and Reproduction
have become impressed on each organism as a result of the
conjoint actions of all external agents, and the conjoint
reactions that each organism has shown to such actions.
The sum total of these actions and reactions causes evolu-
tion, equilibrium or devolution in each organism, either
temporarily or permanently, up to the period of death.
Each of these factors can now be briefly reviewed.

I. HEREDITY.

Since, in the gradual evolution of the earth, the sim-
pler inorganic compounds were formed step by step as
cooling and crystallization proceeded, so in the varied and
long continued actions and reactions between organisms
and the sum total of their environment, definite structures
have been built up that show definite structural details so
long as the environment remains fairly constant. For it is
undoubtedly true, in the past history of the world, that
there was a time when such inorganic bodies as carbonate
of lime, sulphate of soda, or potassium phosphate did not
and could not exist, owing to unsuitable environal condi-
tions. But given the needed environal states, the simpler
constituents of these bodies united into stable union and

14 Evolution and Distribution of Fishes

through subsequent periods up to the present have been
preserved. In exactly similar, though in greatly more com-
plex manner, definite simpler organic constituents have
united into highly complex unions that remain morpholog-
ically identical with each other, so long as like environal
agencies operate on them and cause like response by the
organism.

In the case of fishes and of the more primitive types
that lead up to them, long eons of slow evolutionary action
and reaction had to elapse, after the simplest organisms
were evolved, before sufficiently complex bodies were built
up that could act as the complex progenitors of nemerteans
and later of fishes. But at each step in the process definite
organisms, characterized by definite structural details, be-
came equilibrated to an average environment and thus con-
stituted a species-type that reproduced its kind. Thus
myriads of individuals might show through long ages a
heredity or similarity of detail.

Alike for nemerteans, for primitive and even degraded
fishes like Amphioxus, for cyclostomes, for dipnoans, and
for some ganoids, a surprising similarity in hereditary
details has evidently persisted through long ages, so that
individuals belonging to each of these groups all retain
at the present day close resemblances of hereditary struc-
ture, even though scattered widely apart over the world.
Therefore, though no traces of the first three groups named
are surely met with in the fossil state owing to the soft
nature of their body-substance, their structure, embryology
and distribution clearly proclaim them to be very ancient
forms that still exhibit a surprising constancy of heredity
for each group. They thus become of high importance,
as indicating the pathway of evolution pursued by related
forms that have been entirely blotted out, owing to adverse
and destructive environal surroundings.

II. ENVIRONMENT.

But some of the above individuals, by environal change,
might be so altered in their complex organic constituents,
that new details of bodily organization would appear.
Thus freshwater fishes that live in and are exposed to

Introduction 15

strong currents of cold water in high alpine regions develop
details of structure that greatly resemble each other, even
in groups that otherwise are systematically apart. Again
marine teleosts that have in recent ages become environally
adapted to life amid the brilliant colorations of coral cliffs,
coves and recesses, now rival in tint and not unfrequently
in grotesque structural modifications, the seascape that sur-
rounds them. The past forty years also have revealed
to science those remarkable groups of deep-sea fishes, which
while differing in important details of taxonomic heredity,
agree in the huge eyes and other structural features (p.458)
that environally have formed in response to the dim light
conditions of the deep sea. Though biologists have often
disputed over these and many like acquired structural de-
tails, till their wordy disputations have almost rivalled those
of the medieval "philosophers," these modifications all
proclaim exact actions of varied environal agents that affect
and slowly modify the organisms involved. The manner
in which such modifications are effected will concern us
under the next or third heading.

III. PROENVIRONMENT.

The writer has shown in another work (7:188,194,
205-242,629-651) that in all organisms a correlating and
synthesizing action proceeds which he has designated the
Law of Proenvironment. Least evident and simplest in
action amongst the lowest plants, it becomes increasingly
important as one passes to the simpler animals or the
higher plants, and thence onward to those more evolved.
For in the numerous actions or environal stimuli to which
every organism is exposed, it becomes increasingly neces-
sary that these stimuli be more and more quickly linked
together into a single correlated reaction-response that the
organism can make to such stimuli. This correlation and
combination-capacity exists in feeble and sluggish manner
in the protoplasmic network of simplest plants; becomes
largely concentrated in the chromatin-nuclear substance
of nucleate plants and lower animals; is still more con-
densed in the nerve cells of the simpler animals; and reaches
its climax in the complex groupings of nerve-cells that make

i6 Evolution and Distribution of Fishes

up the brain-masses of higher invertebrates and of verte-
brates.

As will be traced in a succeeding chapter, and as the
writer has already shown in the above-cited work, the
highly complex brain-masses that characterize the nemer-
teans, and above them as well as derived from them, the
fishes, give to all of these the capacity to receive numerous
diverse stimuli, to pass these quickly to the correlating and
combining brain centres, and therefrom to proenviron or
project a path of action for the time that is most satisfying
to each organism involved. So if the sum-total of environal
stimuli conduces to progressive advance and improvement
in the adaptability of an organism to its environment,
evolution results; if the environal stimuli and the hereditary
details are in balanced relation organic equilibrium results;
if the summated stimuli tend to cause disintegration, sim-
plification, and inadaptability to an advancing environment,
degeneration ensues.

Amongst Nemerteans, and every group of fishes, abun-
dant exhibitions of the above law are seen. Thus the lithe,
active and quickly adaptable movements that we associate
with most Teleosts represent the action of many environal
agents — not least of predatory enemies — through many
millions of years, which have acted on every hand as en-
vironal stimuli. These stimuli, almost instantly conveyed
to the great correlating centre or brain, have there been
combined into a single resultant response that may cause
each animal so to move as to escape from three or more
dangerous enemies on different sides; to glide rapidly from
noxious gases, hot waters and falling dust passed Into sur-
rounding waters, toward a body of water free from such
injurious agents; to dart suddenly from a dark position
to a lighted place where some food-animals are disporting,
and to seize accurately one or more of them. In short,
on slight reflection, it will be patent to every one that most
of the acts of fishes as well as of other animals up to man
himself, are truly complex or summated proenvlronal re-
sponses, due to a relinkage and recombination of energized
molecules, in definite nerve centres, where such summating
relinkage occurs. So while every stimulus applied to a

Introduction 17

nemertean or fish constitutes a physical or physico-chemical
(including it may be a complex physico-chemical or organic)
action, the ultimate behavior of each animal to such con-
stitutes a proenvironal reaction or response.

IV. SELECTION or selective survival.

This contributory factor to the great Law of Penta-
morphogeny has been so fully dwelt upon by Darwin,
Wallace and subsequent students, that only a few notes
need be added here. In its actual and exact working as a
phase of Pentamorphogeny, it has not unfrequently been
brought in to explain facts that pertain to the other four
phases, and in its strict application it is largely a secondary
or derived factor that depends on the earlier action of
some one of the four other factors. Thus the plates and
spicules of some nemertean and of some primitive fish
species are primarily chitinous or calcareous deposits within
cell cavities, that represent superfluous products of meta-
bolism. But disliked by opposing animals, and offering a
certain resistance in attack, those forms have slowly become
dominant in which the deposits have increased in amount
and in exactness of deposition. Then the process of natural
selection steadily proceeded, till now only the cyclostomes,
and a few simplified scaleless derivatives from originally
scaled types of fish, represent groups that survive by shelter-
ing in mud, in sand, in holes, or as for the Hag Fishes by
exudation of abundant mucilage and adoption of a parasitic
habit.

The abundant secretion of mucus, the evolution of elec-
tric organs, the production of defensive or of — as in the
chimaeroid sharks — offensive spines, are* in part proenvi-
ronal adaptations, but secondarily become of prime im-
portance in the life-struggle, as being conditions that favor
perpetuation of the species which develops these to the most
appropriate degree. Similarly the protective coloration,
alike as an offense and as a defense arrangement, seems to
represent primarily a proenvironal response to the action
of certain surrounding light rays, but secondarily may de-
termine, by action of natural selection, either the continued
life or the death of a species.

i8 Evolution and Distribution of Fishes

In some cases even it seems to be undoubtedly true that
what at one time aided powerfully in defense might become
by degrees a burden, and ultimately an impediment to
life-activity and survival. Thus the heavily armored and
unwieldy Cephalaspids, Pterichthyids, Dinichthids, and
Titanichthids of Devonian age (pp. 129) largely survived
up to a certain stage, owing to steadily increased arma-
ment. But the very weight of this caused them to become
bottom feeders, which gradually were blotted out along-
side more active and predaceous elasmobranchs and ganoids.

Natural selection then, or selective survival, is largely
a secondary and passive agency in the great pentamorpho-
genic act that organisms are molded by, during their entire
life period.

V. REPRODUCTION.

Our knowledge of this phase of pentamorphogeny —
so far as it concerns animals — is still largely in the making.
The writer has given a few reasons for regarding it as an
important factor for plants. In his "Descent of Man,"
Darwin advanced arguments in favor of "Sexual Selec-
tion," but the potency of this has been very variously
viewed by later authors. The fact has long been known
that amongst fishes a sexual dimorphism of marked kind
may exist. This also becomes associated with structural
differences that must tend to upset the specific equilibrium
of the bisexual individuals. Thus the claspers and dorsal
spines on the males of various Rays, the bright coloration
of the males of some Teleosts during breeding season,
the at times smaller size of the males as compared with
the females as in the Bowfin {Amia calva) , the enlarge-
ment of the oval fin in the male of Polypterus, and not
least the nest-building habits of the Stickleback and of
various African fishes, give rise to structural differences
that must more or less tend to variation in the type. But
until wider studies are forthcoming it would be impossible
to estimate the potency of these details as evolutionary
factors.

The capacity for artificial hybridization between species
of a genus has been definitely established for Salmo by Day

Introduction 19

and others, while repeated descriptions have been made of
supposed natural hybrids between distinct species, as for ex-
ample with the snappers {Liitianus) of Cuba. So far as
at present known however, these are rare and exceptional
conditions.

But it should be borne in mind that we are still largely
ignorant as to the possible effect of changed environment
on the eggs and young of nemerteans and fishes. Graham
Kerr has pointed out (5:8) that this embryonic stage may
also be the most susceptible in the history of individuals
and species. An extensive field for experimental study is
here open.

Having briefly reviewed the above important biologic
conditions it can now be stated that the four fundamental
theses of the present volume are: (a) that the Nemertinea
are the progenitors of all the chordate groups, including
the Hemichordata, the Urochordata, the Cephalochordata
and Euchordata, (b) that the freshwater and land Meta-
nemerteans of the present day represent direct descendants
of related forms that evolved from simpler though envi-
ronally similar freshwater types, but which also gave off
outliers that passed into marine surroundings and there
evolved numerous new genera and species; (c) that from
the higher freshwater Metanemerteans the Euchordata
developed, and long remained wholly or almost wholly
in like freshwater environment as their metanemertean
ancestors, (d) that in process of this development the
Euchordata early separated — probably in late Cambrian
or early Ordovician times — into two divergent groups, the
Cyclostomata and the Gnathostomata, and that representa-
tives of both still exist. Though outside the field of the
present work, but already dealt with by the author (/:
454-474) it might be added that he regards freshwater
cyclostomes allied to Petromyzon or some nearly related
and diverging series, as the progenitors of the Amphibia
and still later of the Mammalia. A few words can now
be added regarding the four above positions, preliminary
to their detailed consideration in subsequent chapters.

(a) Under the first heading it can be said that the
Metanemertinea is the only group of invertebrates which

20 Evolution and Distribution of Fishes

shows a fundamental structural basis, in nearly every detail,
on which could continuously and gradually be evolved or
built up those characters which we associate with euchor-
date or vertebrate organisms. For whether one compares
the ectodermal or skin derivatives, the brain and nervous
systems, the alimentary canal with associated gland tissue,
the proboscis sheath — or rhynchocoelom — as forerunner of
the notochord of vertebrates, the proboscis as sub-
sequently modified in part into oral structures and in part
into the pituitary body of vertebrates, the blood vascular
system, the excretory system, the origin and fate of the
reproductive elements, and finally the development of the
embryo, all exhibit homological details and continuity that
are approached by no other group of organisms.

(b) Under the second heading, the writer would draw
attention to the facts and arguments already adduced by him
which showed that a freshwater environment was the prim-
eval ecological arena in which evolved all of the important
animal groups. But on first sight it might seem vain to
advocate a freshwater origin for Nemerteans in light of
Burger's synopsizing statement ((5: 481) thus: "The
Nemerteans are almost exclusively inhabitants of the sea.
We ought so to express it, because out of 406 assured
species, which are at present known, only 7 live in fresh-
water, 8 on land, and i as a parasite in a freshwater snail."
But it should be said that the Rhabdocoela, which are
evidently progenitors of the Nemertinea, include to-day a
majority of freshwater species, and may well have included
a preponderating majority in former ages, when all the cir-
cumstances of the case are considered. Further, the writer
has shown that alike amongst sponges, coelenterates, poly-
zoans, worms, crustaceans and other groups, the simplest
known types are still freshwater inhabitants, even though
they may now be few in numbers there. So though the fresh-
water and land nemerteans are now poor in genera and
species, compared with marine ones, this need not cause us
to consider that such has always been true in past geologic
times. It rather seems to be true that from a more primi-
tive freshwater rhabdocoel ancestry two main evolutionary
lines of nemertean specialization started. One which in part

Introduction 21

remained freshwater or became lymnicolous evolved ulti-
mately as the Metanemertinea not a few of which gradually
became marine, another seems early to have migrated sea-
ward and evolved as the Protonemertinea. This in time
gave off two evolving but diverging lines that gave rise to
the Mesonemertinea and later to the Heteronemertinea.

(c) Under the third heading it must be acknow-
ledged and accepted that between the simplest living Eu-
chordate type and the highest metanemertean there is a
wide gap, even if we include fossil forms like Palaeospon-
dyhis, Lanarkia, and others described on later pages
(p. 112, 121). But when we include the Ammocoetes
larva of Petromyzon, that of the marine Ascidians, also
the larva and adult state of Amphioxus the gap becomes
much narrower. If further one considers how long-con-
tinued and enormous have been the denudation, destruc-
tion, and rearrangement of land areas; equally the organic
stresses, denudations, and obliterations; also the many mil-
lions of years during which these processes have continued,
the wonder should be rather that the record is so complete
for such soft-bodied animals. It has likewise been ac-
cepted, almost without question, that Palaeospondylus and
Lanarkia as well as other primitive fossil fish genera were
marine. The writer adduces evidence later on which proves
that all of them remained for long ages as freshwater
organisms, and only slowly evolved sidelines that passed
into the sea, and were able to survive there alongside
varied competitors.

(d) Under the last heading we need only at present
reiterate the view which has been generally accepted by
zoologists, viz. that the primitive line of fish evolution
early split up into at least two steadily diverging branches.
One of these probably continued long and wholly in fresh-
water surroundings, and unquestionably must once have
Included numerous genera which made up the group now
known as the Cyclostomata. For only on this hypothesis
can we account for the structural details of the various
genera that now make up the group. While some living
species, according to Gage, are free-swimming and In no
sense parasitic, the gradual perfecting of a suctorial disc,

22 Evolution and Distribution of Fishes

such as occurs more or less from rhabdocoel Turbellarians
up to larval amphibian tadpoles, inclined some to a semi-
ectoparasitic and later to a purely ectoparasitic freshwater
life. That this change took place somewhat recently is
suggested by the fact that parasitism is made on teleost
fishes, which began to evolve in Jurassic and early Cre-
taceous time. As these Teleosts — descended from more
ancient freshwater ganoid ancestors — gradually migrated
seaward, the ecto-parasitic fishes evidently kept attachment,
and in time became modified into the endoparasitic and
highly predatory myxinoid group, which now appears to
breed in the deep seas.

From ancient representatives of the above Cyclostomata
we would trace the evolution of primitive and later of
evolved amphibians, which from present knowledge evi-
dently developed from Mid-Devonian to early Permian
time.

A second group, that must early have diverged from
common ancestors with the Cyclostomata, gave rise to the
main stock of gnathostome or jaw-bearing and toothed
fishes. These, as traced in succeeding chapters, had al-
ready attained to a fair degree of piscine organization by
late Silurian time; and purely amid a freshwater environ-
ment. Subsequently this main stock split up into classes of
gnathostome fishes, from some of which all of our living
representatives have arisen.

Related Geological Conditions 23

CHAPTER II

Geological Conditions in Relation to the
Evolution of Fishes

The first clear evidence we have of fossil fish remains
is in rocks of upper Silurian age. The celebrated fish-
beds or bone-beds of the Downton series in England, of the
Kincardine series in Scotland, of the Waterlime in North
America, and of the Oesel beds in Russia, suddenly reveal
a varied and bizarre variety of fishes, of which we now
have no direct living representatives. Such occurrences
prove that long anterior to the time of deposition of
these beds, still more ancient and ancestral forms of fish
had evolved from some phylum or phyla of the inverte-
brates. This must have occurred during Ordovician,
or even during Cambrian time.

So in chapter 3 the writer extends his previously pub-
lished proof that the Nemertinea is the invertebrate group
from which all of the chordate or notochordal divisions
have started. As existing at the present day the number
of nemertean genera is forty-two and of species fully four
hundred. But since all of those now existing have soft
and readily decomposable bodies, they would leave no fos-
silized traces in the rocks, or might at most and under
rare conditions have their firmer tissues indicated. For
the occasional preservation of medusoid, of trilobite, and
even of soft fish tissues has already been demonstrated.
Similar nemertean remains, however, are still unknown,
unless indeed some of the "conodont" genera are the teeth
of nemerteans or of primitive cyclostome fishes.

A few amongst other reasons for regarding the Nemer-
teans as being an ancient group geologically are: — (a)
representative living species occur in practically every part
of the world, and this suggests a slow but extensive dis-
tribution, and gradual adaptation to environal surround-
ings, of existing genera; (b) two genera and fifteen species
are either freshwater or terrestrial in habitat, though the
majority are now marine littoral dwellers, while two genera,
Pelagonemertes and Malacohdella are pelagic; (c) even

24 Evolution and Distribution of Fishes

If we confine attention to the freshwater genus Sticho-
stemma, the seven known species occur In Pennsylvania,
Britain, France, Germany, Austria, Switzerland, Russia,
Turkestan and East Africa. The terrestrial genus Geo-
nemertes Includes seven species distributed over the Ber-
mudas, Rodriguez, the Palau Isles, New Zealand, Aus-
tralia, New Guinea, and Samaral Isle. The littoral marine
species are world-wide, and even such genera as Prostoma
{Tetrastemma) with 63 species, Cerebratulus with sixty-
three species, and Amphiporus with sixty-three species are
all represented by some species over every littoral region.
The marine genus Tiibtilanus Is represented by species
from the frozen seas of Greenland southward along the
Pacific and Atlantic coasts to the tip of South America.

Such considerations at once cause us to Inquire whether
the earth has undergone fundamental changes — alike of
elevation and depression — in the past; whether the main
landmasses have — as claimed by the earlier geologists —
remained largely as they now are throughout geologic time;
or rather have undergone extensive alterations, elevations
and depressions, denudations and rearrangements, as
claimed by Freeh, de Lapparent, Arldt and other recent
writers; whether the same geologic agencies as we now
observe were equally or more or less active In earlier
times? The remainder of this chapter will be devoted
to these and to related themes, while later chapters will
elucidate the subject further.

I. The primitive plastic crust.

No matter what view may be accepted as to the origin
and condition of the earth prior to the appearance of plant
and animal life on It, all present physical, geological and
palaeontologlcal facts Indicate that the surface crust, from
Archean to Permian time, was more plastic, uniformly
extended, and subject to variations in marine, freshwater,
and terrestrial conditions than during recent epochs. This
plastic nature of the crust prevented the formation of deep
depressions and equally of lofty mountain ranges that are
both Inimical to rapid organic evolution and activity. So,
even if It be granted that denudation has worn away the

Related Geological Conditions 25

higher palaeozoic hill-ranges, and has filled up the de-
pressions of ocean beds, the practical absence of a high
alpine and of an abyssmal flora and fauna In palaeozoic
and even more recent rocks Is partial proof of plastic
crustal conditions.

But more striking still is the frequent alternation, within
a few feet or even inches in rock thickness, of numerous
layers that may differ markedly in mineralogic composi-
tion, or that may yield a typically lacustrine fauna from
one bed, a marine fauna from another immediately above
or below, and then a series of beds that differ from these
as well as from each other, but which may be largely or
wholly devoid of organic remains. Such conditions are
eminently typical from the Silurian to the Permian or
Triassic epoch, but seem to reach a climax from the Upper
Devonian to the close of the Carboniferous, and again
become marked during the Jurassic epoch. The truth of
this is attested in all of the detailed accounts of rock-
sections given by geological surveys, in the articles of geo-
logical magazines. In technical reports on commercial min-
eral strata, and has often impressed the writer — as doubt-
less it has Impressed all field workers — when travelling
over and examining successive rock sections for their or-
ganic contents.

This relatively plastic and changeable condition was
clearly due in part to the thinness, and highly faulted
nature, of the early sedimentary crust; in part to the very
extensive exhibition of volcanic activity that then prevailed,
as compared with Its localized and reduced exhibition at
the present time. Thus geologists are agreed (Gelkle,/:
861-907 ;Chamberlin-Salisbury, 6* :II :i75-i94, etc.) that the
Archaean rocks often represent a thickness of about 21,000
yards or 12 miles, as compared with 15,000 to 20,000
yards as the thickness of the formations that make up
more recent strata. These foundational Archaean rocks
are, however, extensively altered, faulted, contorted, and
often even overturned on each other. During the Ordo-
vlcian and Silurian periods extensive volcanic change also
proceeded, and the same is true over wide areas of Dev-
onian strata in some continents.

26 Evolution and Distribution of Fishes

One effect of this would be the frequent formation of
fissures for the passage outward of chemically active gases,
and for the percolation inward of chemically active liquids
from the surface. These would hasten the decomposition
and denudation of exposed rocks, at the same time that
other masses were being deposited in freshwater or in
littoral marine areas. Furthermore, the writer has already
emphasized {g :2^g;i i^^) ^^^^ ^^^^ restricted areas of
the present day as the Yellowstone region, the geysers of
Iceland, the terraced hot-springs of New Zealand, and the
thermal springs of Japan, may have been of wide and
frequent occurrence during early geologic times. Though,
owing to subsequent denudation-change, the deposits formed
by them may have left small trace behind, it seems to be
amid such chemically and physically active centers that we
should expect to encounter the first dawnings of life.

II. Geological and early biological relations.

Now from the standpoint of organic evolution, it seems
necessary to accept that primitive plant organisms began
to form during the early part of the Mid-Archaean epoch*;
that these gradually gave rise to higher plants, and later to
the simpler unicellular animals; while throughout the Or-
dovician and early Cambrian periods types had appeared
that were, on the animal side, the ancestral originators
of the graptolites, corals, brachiopods, trilobites, and mol-
luscs of later Cambrian rocks.

Now alike from the standpoints of morphological de-
tail as of neurological complexity, we may regard the fishes
of Silurian age as fairly intermediate between simple non-
nucleate unicellular animals on the one hand, and anthro-
poid apes on the other. The average thickness of beds,
from the base of the semistratified or stratified rocks that
are classified as mid-Archaean to the base of the upper
Silurian may be taken as 70,000 feet, from estimates for
the different formations made by Prestwich, Geikie, Haug,
de Lapparent, Chamberlin, Grabau, and others. The

* The writer throughout will use the term Archaean rather than Proterozoic, as it is
a noncommittal term, and all available evidence indicates that simple cellular plants ap-
peared first, while primitive animal types branched off from these at a considerably
later time.

Related Geological Conditions 27

thickness of beds from the base of the Devonian to those
of recent date may be given approximately as 85,000 feet.
This would indicate that the beginnings of life date well
back into mid-archean or even older rocks. Such is the
conclusion that Patten {10: 23^) has already reached. All
such records, however, are confessedly imperfect and ap-
proximate. The want of record of organic remains in
Archean and even in some Cambrian rocks seems to be
wholly due to the soft perishable nature of the primitive
organisms. Only when sponges, hydroids, or actinioids be-
gan to secrete calcareous or siliceous or chitinous spicules or
tests, when previously protoplasmic echinoderms began to
form increasingly heavy tests as in the cystoids, or when
brachiopods and molluscs started, while in the "phylem-
bryo" or in the "veliger" stage of their phylogeny to
secrete a chitinous and later a calcareous shell, did the
likelihood occur of their being preserved as fossils.

This circumstance greatly complicates the question as
to whether primitive organisms originated in a freshwater
or in a marine environment. The writer has already
shortly set forth his views (7:410) that certainly most
and probably all of the great animal groups as well as plant
groups started as inhabitants of lakes and swamps. Only
secondarily and still later did they migrate into marine
areas, or on to the land. In regard to fishes he hopes
in the subsequent context to prove clearly that such is emi-
nently true for them. With abundant and ever-increasing
material for study of the Crustacea, Arachnida, MoUusca,
and other groups, he hopes also to prove its correctness
in detail for them, as he already has in general outline.

If, then, a decidedly more plastic state of the evolving
crust existed up to Silurian or even Carboniferous times,
such would give rise to several important conditions that
would all be highly favorable to organic development and
change. Thus, as compared with present distribution of
land and sea, a much more extensive expanse of land and
of freshwater areas must have existed above the sea-level,
while the ocean itself — existing as a highly plastic but
heavy and continuous mass — would tend to form sags or
depressions around or between the land areas. These de-

28 Evolution and Distribution of Fishes

pressions must have been much shallower however than the
often deep and at times ravine-like inequalities of the ocean
bed now, that is confined within and between hard and
thick sub-oceanic rock-floors. Instead, therefore, of the
exposed land and water surfaces being as now, in the pro-
portion of I to 3, it seems almost assured that a ratio of
2 in land to 5 in sea would be a conservative estimate. Such
a configuration is set forth to some extent by Freeh in
"Lethaea geognostica."

The land masses, however, in virtue of the plastic
character of the earth's crust, must seldom have been ele-
vated above sea level to more than 3000 or 3,500 ft.,
and even over more extensive areas must have been com-
paratively level, like the eastern part of Central Brazil
and the Congo basin of West Africa now.

Owing also to frequent inequalities and localizations
in deposition of material, with resulting surface stresses,
or from shifting of bodies of freshwater owing to volcanic
strains and upheavals wide expanses of freshwater must
often have extended in the form of lakes, swamps and slug-
gish rivers. These — as will be explained later — seem to have
formed often as wide expanses only a few feet above the
sea level. So when crustal disturbances took place, an
invasion by the sea of such freshwater expanses must often
have caused a sudden and marked change in floral or faunal
characters, that we can frequently read the record of, alike
from the altered nature of the rock-forming deposits, and
the remains of fossilized organisms. The converse re-
sult would naturally happen when slight elevations of
shallow sea-bottoms caused sudden destruction of marine
life, and the ushering in of a lacustrine, or swamp, or terres-
trial vegetation.

The above do not represent vague or hypothetical en-
vironal changes, but are exactly required by, and exactly
conform to, all the evidences before us, when we investigate
the early fossiliferous rocks, and not least the fish and
other organisms enclosed in these. In line also with the
studies of Joly ( 11; 23) on the solution and transfer of
salt from decomposing rocks, and its gradual accumulation
in the sea under constant evaporation action, it should be

Related Geological Conditions 29

borne in mind that freshwater must once have been more
abundant proportionately than now. To what degree this
held true, however, is as yet undetermined.

Ill Primitive freshwater and marine areas contrasted.

But equally in geological, paleontological and biological
writings of the past and present century, the preponderat-
ing extent of the ocean; the highly dynamic action of it
in effecting crustal changes; the supposition that in it all life
originated, and from it all freshwater and land animals
emerged; also that the present ocean beds are fairly con-
tinuous with those of palaeozoic times; have been so in-
sisted on and elaborated, that the possibility of a different
interpretation has seemed superfluous. But reared and
educated as the writer was amid Carboniferous and Old
Red formations, the extensive deposits of these in which no
traces of marine life occurred, but in which abundant and
continuous beds of evident freshwater origin were followed
often through hundreds of feet in thickness, caused him
to query the correctness of the current interpretations.

These impressions however of more than forty years
ago had been somewhat anticipated, and were succeeded
by like queries of other investigators. Thus, in the careful
and elaborate monograph by Rupert Jones on the Esther-
ieae {12) constant emphasis is laid on the freshwater
habitats of all existing species, and apparently also of all
species described from Old Red rocks upward. But the
usual presence and admixture with these of abundant fish,
eurypterid, and plant remains, some of which, and par-
ticularly the fishes, had been directly or tacitly claimed as
marine, constantly inclined him to hesitate in his final de-
cisions. And a like attitude was assumed by him in a more
recent article.

A. Geikie, with wide experience as a field geologist as
well as a writer, in viewing the fish remains and associated
organisms of Old Red age, fully accepted a lacustrine habi-
tat for these, and so he designated their Scottish areas
of occurrence as Lake Orcadie, Lake Caledonia etc.
{7; 1008).

30 Evolution and Distribution of Fishes

The most emphatic query however — likewise from the
geological side — is that of Chamberlin in his paper "On
the habitat of the early vertebrates" (/J; 400) as well as
in many sections of the textbook of which he is joint author
{8; II). In the former, his opening paragraphs were evi-
dently influenced by earlier descriptions of Newberry and
Orton for "Corniferous" beds, and their supposed marine
origin. Detailed reference is made to this in subsequent
pages of the present work (p.p. 126, 129). Later, in his
"Geology" he says {8; II; 482) regarding the Devonian,
— "The general faunal conception is, that in the Appala-
chian tract and in the Canadian provinces lying to the
north-east of it, as well as in Great Britain and Russia,
there were many lodgment basins that were progressively
filled by land-wash and freshwater sediments, and that
these basins were the home of a freshwater or brakish-
water fauna, in which ostracoderms and fishes were the
leading elements, and crustaceans their chief colleagues."
And again he remarks under "the Mississippi period"
(P- 535)'- "Fish appear to have first effectually invaded
the open sea in the Devonian period, but during that period
true marine fishes seem to have been inferior in number and
variety, to those of the inland waters."

Elsewhere, and in another work, the writer hopes also
to quote the modified or limited view expressed by J. M.
Clarke as to the origin and distribution of the eurypterids,
and which advocates the existence of wide freshwater areas
in which these giant arachnids disported.

In succeeding chapters of this work, the question is
fully discussed by the writer, on the ground of evidence
there adduced. But for a proper understanding of the
evolution of fishes in relation to their environment, the
following seem to be requisite conditions: — (a) the earth's
crust was then in a relatively plastic state; (b) as a con-
sequence, the land and sea were more uniformly distributed
than now; (c) high land elevation and deep ocean beds were
as yet alike absent; (d) extensive and connected freshwater
areas existed, and permitted wide migration and resulting
dispersion of freshwater organisms, not least of nemerteans
and fishes; (e) the extended and fairly uniform distribution

Related Geological Conditions 31

of land devoid of cold mountain areas, and of seas devoid
of dark ocean depths, formed the most wide-spread and
favorable environal conditions for active organic evolution.

Geologically then the writer would consider that great
masses of rock strata of Upper Silurian, of Devonian, and
of Carboniferous age are of freshwater origin, and that
these in many cases equal or excel rocks that are clearly
of marine origin. Thus the Scottish deposits described by
Campbell in Kincardineshire (/-/; 923), the corresponding
Downtonian beds of Central England, the Niagara and
Waterlime strata of North America, those of Oesel in
Russia, also some Swedish beds are largely or wholly fresh-
water. The extensive deposits of Old Red or Devonian
rocks over the Northern United States and Southern
Canada, over North and Central Scotland, Ireland and
some parts of England, those of Russia and Germany also
are of similar origin. Some of the Lower Carboniferous
or Misslsslpplan of North America, the Calciferous of
Central Scotland the Culm of Austria and parts of
Germany, as well as the greater extent of the enormous
deposits that make up the True Coal Measures of North
America, of Europe, of parts of Asia and of Australia
should be similarly classified.

The truth of the above Is In part proved by the habitual
absence of marine organisms; by the uniform presence of
a biological assemblage that Is treated of In detail In some
succeeding chapters; by the frequent direct continuity in
structure, in mode of life, and In habitat of such groups
as the Coelacanthldae, the Palaeoniscidae and represent-
atives of the Dipnoi (Dlpneustel) , from Devonian or
Carboniferous days on to Cretaceous or even recent time.
Abundant proof of such will be adduced later.

It might well be objected now, that if such conditions
existed during palaeozoic or even more recent epochs, ex-
amples possibly should be left still, that would more or
less parallel or reproduce the above. Such seem largely
to be fulfilled In the group of fishes that has come down
from early Old Red times to our own day as the DIpneustei.
The three living genera and all the species of these, inhabit
wide areas of South America, of West and Central Africa,

32 Evolution and Distribution of Fishes

and of Australia, that are either semi-lacustrine expanses,
or are subject to periodic floods annually or for short
periods, during which time considerable transfer of detritus
and rock-forming materials occur. The observations of
Baldwin Spencer, of Graham Kerr and others, along such
lines will be referred to later.

But as depicting the possible geological changes effected
where the Australian dipnustean Neoceratodiis occurs,
Spencer's description {15; 81) deserves quotation. He
says, regarding the wide flood-plain of the Burnett river:
"In the rainy season, the creeks, dry in summer, become
converted into roaring torrents; the river rises suddenly,
as much sometimes as 50 feet in a very few days, and down
from the hills and the country round an enormous amount
of sand is swept suddenly into the water. When once the big
sandbanks of the river have been seen in dry weather, it
is easy to realize what a vast amount of sand must be swept
down into the stream at flood-time every year."

While many of the larger rivers of the present day show
an equally marked rise and fall of the waters, some develop
flood plains of much greater extent than the above. Thus
the Amazon may spread in places to a width of 300-400
miles during the wet season, while it as well as the Congo,
Niger, Zambezi and many smaller rivers, may form exten-
sive lakes that vary from shallow marshy areas to sheets of
several feet in depth. These, as now existing, give us some
faint idea of the enormous geologic changes that must have
gone on at a greatly more rapid rate during the palaeozoic
period.

As will appear later when the physical and biological
environment of fishes is traced out, it is highly probable
that the remains of many of these were stranded over such
flood-plains as the above. They may then have been covered
by a deposit of mud, or muddy sand, or of fine sand, and on
retreat of the waters to their regular bed, the deposit
might have been exposed to hot suns which would cake
together the whole of the enclosed fishes. Later on, and
within a few days at most, the entire mass would become
dried and preserved in comparatively natural positions.

Related Geological Conditions 33

So it may well be inferred that, over wide continental
areas both of the northern and southern hemispheres, ex-
tensive river systems drained wide regions of comparatively
low land, and that in their course they may have formed
huge marshy lakes of varying depth but temporary duration.
When these flood-plains or swollen lakes dried up masses
of fish may have become stranded, buried under the finer
mud deposits and then dried under hot suns, thereafter to
undergo fossilization in at least some cases.

IV. The geologic age of continents.

Another widely discussed and greatly disputed problem
in geology has been the relative permanence of existing
continental masses, as compared with the possible former
distribution of land and sea in a totally different manner.
From the biological standpoint, and not least from that of
the history and dispersal of fishes, a fundamentally different
disposal of the great land'areas from that of the present or
of recent time, is a prime necessity that will become evident
as we proceed. So the outline charts suggested by Neumayr,
Schuchert, de Lapparent, Freeh and others, as being ex-
planatory of past land and sea areas, have much in their
favor, and especially so in connection with the gradual
evolution and distribution of fishes. Though only approxi-
mate in exactness probably, they are of extreme value, and
will be reproduced in unaltered or in modified form, as
occasion requires in the succeeding text.

The hitherto prevalent view that fishes as a group origi-
nated in the sea, could most easily be supported in a super-
ficial manner on the hypothesis that the existing oceans are
fundamental and are ancient reservoirs of salt water, from
which successive races of fish could pass inward to the rivers
and lakes of encircling land masses. But geologists and
zoologists have alike failed to realize, that those genera
which show at present the most marked tendency to pass
from a saline to a fresh-water environment, belong to larger
aggregates which are mainly fresh-water inhabitants. Thus
the lampreys, the sturgeons, the salmon, the shad and many
other anadromous fishes have had — as we shall later show
— a freshwater origin and history up till now.

34 Evolution and Distribution of Fishes

Furthermore, the passage Inland of such fishes is for the
performance of that most important and primary life-
function — the reproduction of the species. All known evi-
dence indicates, that the inland situation sought out for the
spawning act represents a habit of ancient and hereditary
character, which antedates the period when such animals
tended to pass from a freshwater to a marine life.

V. Terrestrial oscillations and stratigraphic successions.

In the development of geology as a science during the
past century of effort, thick rock sections have often been
hurriedly examined and charted; fossils found in some
stratum of the section have been mixed with others from
higher or lower strata; inaccurate statements have often
subsequently been made as to the exact zone where the
fossils were found; while not unfrequently a single and *at
times even thin stratum with its organic contents, has been
described as typical of the entire section. But during the
past thirty years, as more exact methods of observation
and recording have been introduced, every changing type of
rock is duly described and measured even though only a
half inch to inch in thickness. In studying these on their
charts then, one is often surprised or at times even puzzled,
by the apparent suddenness and sharpness of the transition
from one palaeontological facies to another, and not un-
frequently also from one to another and different type of
rock. These are indications of the frequent oscillations that
have occurred in the earth's crust, and of the suddenness
with which one congeries of organisms may have been
blotted out, and another ushered in, that may have differed
markedly in ecologic and taxonomic affinities from the
former. Neglect to correlate, in exact stratigraphic succes-
sion, the organisms that are typical for each stratum passed
through, has been the main and a fertile source of erroneous
opinions in the past.

On the other hand, the continuous persistence over wide
areas of Europe and North America of thin strata, that
possess a uniform lithological character, and that enclose
fossils of highly typical nature, often furnishes valuable
means for determination of the successional relations of

Related Geological Conditions 35

thicker strata above and below. No better example of such
can be adduced than the so-called "bone beds" of Silurian,
Devonian and succeeding epochs. These are often crowded
with entire teeth, scales or bones of well-recognized groups
of fishes, or with the crushed fragments of these. Extend-
ing often in stratigraphic continuity over hundreds of square
miles of territory; at times repeated in character, with a
few inches or even feet of strata intervening between them
till four or five bone beds may be recorded in a section 50
feet to 100 feet in thickness; they furnish evidence of the
teeming abundance of fishes to a degree that almost staggers
conception. Numerous cases of their occurrence will con-
cern us later, while it is with some of them that the
palaeontological record of fishes first opens.

Remarkable features of practically all of these, "Bone-
beds" are that the rock-matrix is of an extremely fine and
often fissile texture; that it is often so hard and close-
grained as to give out a metallic ring when struck; and that
while in some cases the matrix is jammed with teeth scales
or bones, in others the matrix is finely laminated, and carries
between the laminae perfectly preserved and flattened fish
or other remains.

Murchison, in describing the English Downton beds of
the Ludlow series says : "The highest member of the Ludlow
rocks is the most interesting Inasmuch as until recently It was
described by myself as being the oldest rock in which fossil
fishes had been found. The only exception Is that already
alluded to — the occurrence of a fragment of Pteraspis in
the central part of the same formation. The uppermost
Ludlow rocks also contain the earliest remains of land
plants. The lower layers of this zone, as seen at Ludlow,
are finely laminated, earthy, greenish-gray sandstones, con-
taining a few ichthyolites with several shelly remains
characteristic of the formation. It was the middle part
only of this band, or a gingerbread-colored layer of a thick-
ness of three or four inches, and dwindling away to a
quarter of an inch, which exhibited, when my attention was
first directed to It, a mottled mass of bony fragments, for
the most part of small size, and of very peculiar character.
These, with a few remains of shells and crustaceans, includ-

36 Evolution and Distribution of Fishes

ing Pterygotus problematicus^ occur in a cement in which
varying proportions of carbonate of lime, phosphate of lime,
iron-oxide, and bitumen are disseminated." The writer
has cited the above as being one of the earliest descriptions
of some of the most ancient fish beds, and also as referring
to peculiarities that will be treated of later,

Rohon says (6/ : 4) in his paper entitled: "Die obersil-
urischen Fische von Oesel" that the beds are divisible
into two zones, a lower or Wenlock, and an upper or
Ludlow. The former shows no fish remains. The latter^ —
which is again subdivided into two zones — shows in one of
these abundant animal remains. Alike at Rotzikiill near
Kielkond, in strata known as "Wita-steinbruch," also at
Wesiko and Hoheneichen, some strata are charged with
fossilized animals that include Ceratiocaris nottingi,
Eiirypterus fischeri, Pterygotus osiUensis^ Bunodes lunula
and rugosus^ also in one or other of the above localities,
and in association with the above or related types, a rich
variety and quantity of such primitive fish-genera as
Thyestes, {Auchenaspis) , Tremataspis,, Coelolepis, The-
lodus (Pachylepis), Oniscolepis, etc. The delicate details
of sculpturing on the exoskeletal plates of these, prove
that they must have been quickly and perfectly preserved
after death. The "Wita-steinbruch" of Rotzikiill he de-
scribes as a very uniformly stratified, fine-grained, yellow-
white dolomite, which readily absorbs water, but when dry
Is very hard and breaks under hammer-blows into irregular
pieces of different size and form. One naturally asks then
as to the nature and mode of origin of such rock-strata.

Beds described by Traquair, and which the writer has
examined near Loanhead, Edinburgh; also the celebrated
Solenhofen and Eichstadt slate deposits, with others in
Russia, Australia and elsewhere all closely agree in texture,
and in their abundant fish fauna. The usually exquisite
state of preservation of the fossils, not least of the fishes,
has often been commented on.

While in some cases, as with the Downton bone beds, the
fish remains are piled together in confused masses, in many
instances the animals are preserved entire, and are of all
sizes from two or three inches up to as many feet.

Related Geological Conditions 37

Now the writer has watched through successive days, the
changes effected in fishes that have been thrown up, and have
become high and dry along the shore-lines of marine areas.
He has also noted along estuarine banks, over lake margins,
and to a less extent though with sufficiently informing out-
come, over the floodplains of rivers and streams where fishes
had been stranded, likewise in two notable instances along
streams where thousands of fishes had been poisoned by
chemical products thrown out from mills along the banks.
In all cases within eight to ten days nearly every trace of
these had been destroyed, by the joint softening, disintegra-
ing and mechanical action of rain, dew, bacteria, small
crustaceans, insect larvae and higher animals. Rarely one
can note a gradual but yet sufficient deposit of mud, sand
or lime that can cover and conserve the firmer parts while
the softer decay.

VI. Volcanic dust and the preservation of organisms.

Even if we accept the action of the above agencies,
some more rapid, widespread, and perfect mode of destruc-
tion, enclosure and permanent preservation of fishes, as
well as other organisms, seems to be called for, as an im-
portant geologic and palaeontologic factor. Mention has
already been made of wide-spread volcanic action during
palaeozoic times. And though less violent and extensive,
according to present knowledge in its surface manifesta-
tions, this action was continued into mesozoic and more
recent periods with at times cataclysmic results.

Now nearly all of the historic and cataclysmic volcanic
outbreaks of the past two hundred years have been ac-
companied by copious discharges of poisonous gases, by
upheavals or explosions amid terrestrial, lacustrine, and
marine strata that mechanically have caused widespread
death of organisms over thousands of square miles. In
nearly every case also there have been shot into the air
enormous quantities of fine volcanic dust of varying com-
position, that became redeposited as beds which have varied
from seldom less than an inch to one hundred feet or more
in thickness.

38

Evolution and Distribution of Fishes

In geological treatises such deposits have been referred
to and in some cases described at considerable length.
But their importance as possible conserving agents from
the palaeontological standpoint seems almost wholly to have
been overlooked. A somewhat detailed consideration of
them seems therefore to be appropriate here.

As to the nature of the volcanic dust, this varies greatly
according to locality, and the composition of the crustal
rock that has undergone pulverizing. But as granitic masses
constitute a large portion of the foundational crust of the
earth these must most commonly have been reduced to
powder and exploded from vents. The following table,
therefore, is arranged to show the chemical composition
of a series of granitic rocks.

Si02 . .

70.60

72.24

74.82

73-38

71.90

73-27

66.83

71.62

71.83

AI2O3 . .

16.40

14.92

16.14

14.86

14.12

15.51

15.24

14.99

15.27

Fe203 . .

1.52

1.63

O.IO

1.20

0.33

2.73

1.27

1.25

FeO . .

0.36

0.23

1.52

1.64

0.86

1. 14

1.66

1. 01

I. OS

MnO . .

0.48

0.32

0.05

trace

O.IO

0.17

0.22

MgO' . .

1. 00

0.36

0.47

0.23

0.33

0.15

1.63

0.74

0.73

CaO . .

2.47

1.68

1.68

0.89

1. 13

2.74

3-59

1-33

2.06

Na20 . .

4.14

3-51

6.12

3-94

4.52

4.70

3.10

3.62

4.21

H2O . .

4.29

5. 10

3-55

3.89

4.81

1.66

4.46

4.81

4.07

The above shows that silica, alumina, and iron oxide

make up about 90 p.c. of the total granitic mass. It is

Constituents No. i No. 2

Silica (Si02) 7i-i5 68.91

Alumina (AI2O3) and Iron (Fe203) i5-95 6.12

Lime (CaO) 0.85 3.44

Magnesia ( MgO ) 0.41 ....

Manganese (MnO') trace ....

Potash (K2O) 3.36 0.36

Soda (Na20) 4.94 3.09

Organic Matter 8.75

Sulphuric Acid (SO3) 8.88

of interest therefore to compare with this the analysis of
two samples of volcanic dust as given by 1. C. Russell in
his valuable and original work (77:292), No. i being
from Truckee Canyon, Nevada, and No. 2 from Nebraska.

Related Geological Condition^ 39

The close agreement of Table i with that given for
granite is suggestive. The high percentage of organic
matter (8.75) and of sulphuric acid (8.88) in Table 2
over granite is readily explained when one considers that
the volcanic dust was ejected during Eocene times, and
might readily have been mixed with organic remains of
that period. Proof of this is given below. Again the
amount of lime or of iron may vary, and either may give
a distinct character or color to the rock formed, or cause it
the more readily to recombine with other rocks. Russell
says (p. 286) that in Nebraska volcanic dust covers twenty
counties, sometimes to 50 feet in depth in the southwestern
part of the state, but becomes gradually thinner and finer
when traced eastward. So the volcano must have been to
the south-west.

Geikie again in quoting an earlier and graphic writer
says: — "A vast colunin of exceedingly fine dust rises out of
the crater, sometimes to a height of several miles, and then
spreads outwards like a sheet of cloud. The remarkable
fineness of the dust may be understood from the fact that
during great volcanic explosions no boxes, watches, or close-
fitting joints have been found to be able to exclude it."

As regards the distance to which the dust may be
carried Bonney (/^: 189) in describing an eruption at Mt.
Hecla says: "one, which began in September 1845 lasted for
more than a year, and the ejected dust fell abundantly in
the Orkneys, quite 500 miles away. Copious discharges
of this material seem indeed to be rather characteristic of
Icelandic eruptions." Writing again of the volcanic peaks
of South America he says (p. 241) : "But the most noted
of all is Consequina, for it was the scene of a frightful
eruption in 1835 ... It began on the morning of
January 20th, when several loud detonations were heard,
followed by the ejection of a cloud of inky smoke
The cloud spread gradually outwards, obscuring the sun,
while fine dust fell from it like rain. This went on for two
days, the sand falling more and more thickly, and the ex-
plosions becoming louder and louder. On the third day
they reached a maximum, and the darkness became intense.
The quantity of material that fell was so great that for

40 Evolution and Distribution of Fishes

leagues around people actually deserted their homes, fearing
lest their roofs might be crushed in. At Leon, more than
a hundred miles away, the dust lay several inches deep,
and it was carried to Jamaica, Vera Cruz, and Santa Fe de
Bogota, over an area of 1500 miles in diameter."

When such fine dust falls on the surface of a swamp,
a lake, or the sea, it might be supposed that the whole would
be swept away, and mixed with materials of erosion. But
Judd {ig; 72) has well observed: "Everyone is familiar
with the fact that pumice floats upon water; this it does not
because it is a material specifically lighter than water, but
because cavities filled with air make up a great part of its
bulk. If we pulverize pumice, we find the powder sinks
readily in water." And later (p. 74) after speaking of
oceanic volcanic debris — pumice, dust, etc., — he says: "these
particles of volcanic dust and fragments of pumice, by their
disintegration give rise to a clayey material, and the oxida-
tion of the magnetite, which all lavas contain, communicates
to the mass a reddish tint. This appears to be the true
origin of those masses of "red clay" which, according to
recent researches, are found to cover all the deeper parts
of the ocean."

But it may well be suggested that equally abundant dust
deposits have taken place on land and in lacustrine or in
swamp areas, where they could rapidly entomb and preserve
even delicate organisms. Many evident examples of this
will be referred to later.

The quantity of dust carried and the extent of area
covered have both been fairly accurately estimated. In
addition to statements made above, the following are help-
ful. "In 1882 at Vesuvius the ashes not only fell thickly on
the villages round the base of the mountain, but travelled
as far as Ascoli, fifty-six miles distant on one side, and
Casano, one hundred and five miles on the other." (Geikie
3rd edit. p. 213). In the eruption of CotopaxI on the 26th
of June 1877 the same author says (p. 213) : "At Guayaquil
on the coast, one hundred and fifty miles distant, the shower
of ashes continued till the first of July (i.e. five days). Dr.
Wolff collected the ashes daily, and estimated that at that
place there fell three hundred and fifteen kilogrammes on

Related Geological Conditions 41

every square kilometre, during the first thirty hours, and on
the 30th of June two hundred and nine kilogrammes in
twelve hours. During a much less important eruption of
the same mountain on the 3d of July, 1880, the amount of
volcanic dust ejected, according to Mr. Whymper, could
not have been less, and was probably vastly more, than two
millions of tons."

But Russell's observations (op. cit. p. 285) specially
emphasize the great geological importance of such de-
posits. "In the Sierra Nevada, and over large portions of
the Great Basin, deposits of volcanic dust many feet in
thickness are frequently met with," and these, in part of
Pleistocene, in part of more recent age, become finer and
finer, with increasing distance from their source. Again
( p. 288) he says: "In Alaska and adjacent portions of
Canada, still other extensive deposits of volcanic dust of
recent date are known. The writer, while journeying up
the Yukon River in 1889, observed above the mouth of
Pelly River a conspicuous white band from eight to twelve
inches thick, in the upper portions of the river terraces,
which was traced for fully two hundred miles. This de-
posit of remarkably pure volcanic dust had previously been
noted in the adjacent regions, and was more fully examined
by Hayes in 1881. The various observations show that
it occupies an area of fully fifty-two thousand two-hundred
and eighty square miles, and varies in thickness from a few
inches on its northeast border, to between seventy-five and
one hundred feet near its southwest margin. Its volume
has been computed by Hayes to be in the neighborhood of
one-hundred and sixty-five cubic miles. The volcano from
which this vast eruption of fine dust was derived, is as yet
unknown, but from its distribution, and its increase both in
thickness, and in coarseness toward the southwest, the point
of eruption is judged to be some seventy-five miles north-
west of Mt. St. Elias.

This Alaskan deposit is pure white, except when im-
purities are present, and indistinguishable, at least In its
physical properties, from the similar material found so
abundantly in California, Oregon, and Washington."

42 Evolution and Distribution of Fishes

Russell's volume gives a most graphic picture of volcanic
activity as proceeding in Coenozoic time. But the activity
was undoubtedly much greater and more widespread during
the palaeozoic epoch.

As to the nature of the rocks formed by such dusts, Judd
says {ig; 89) : "Some volcanic materials, when mixed with
water, have the property of rapidly "setting" like concrete.
The ancient Romans and modern Italians, well acquainted
with this property of certain kinds of volcanic dust and
lapilli, have in all ages employed this "puzzolana" as it is
called, as mortar for building . . . The cause of the
"setting" of "puzzolana" and tufa is that rain water, con-
taining a small proportion of carbonic acid acts on the lime
in the volcanic fragments, and these become cemented to-
gether by the carbonate of lime and the free silica which are
thus produced in the mass." Here Judd refers specially to
a variety of lime dust produced by pulverization in volcanic
cavities of limestone and siliceous rocks and extrusion of
this in almost pure lime-silica combination as an Impalp-
able dust. Such then would fundamentally differ from rock
produced by hardening of granitic dust or of a quite pure
lime rock.

That considerable subsequent chemical activity and re-
arrangement may occur in volcanic dust is also noted by
Judd (p. 155) as follows: "Scoria and pumice-stones are
frequently found to be acted upon by acid vapors to such
an extent that the whole of the material is reduced to a
white pulverulent mass. In these cases the oxides of iron
and the alkalis have united with the sulphuric or hydro-
chloric or carbonic acids, the compounds being carried away
in solution by the rain water falling on the mass; the
materials left are silica, the hydrated silicate of alumina,
and hydrated sulphate of lime (gypsum), all of which are
of a white color."

It is well known, and has often been commented on,
that such subaerial deposits, with their preceding or ac-
companying earth shocks, and emission of noxious gases,
rapidly kill organisms over wide areas, and these may then
be found as preserved enclosures. Thus Russell (op. cit.
p. 2 86) after referring to dust-like deposits of volcanic

Related Geological Conditions 43

origin in Utah, often 30 - 50 ft. thick, says that "some
of these deposits are interbedded with lacustrine sediments
of Tertiary age," while those of Washington and Oregon
"contain the leaves of Tertiary plants, or are associated
with lacustral sediments and lava flows in such a manner
as to show that they are of Tertiary age." And again he
says: "The volcanic dust of the Pacific States sometimes
contains the bones of mammals, and is frequently charged
with quantities of leaves, showing that some of the tempests
generated by volcanic agencies were disastrous to animal
and plant life. These and related disturbances in environ-
ment probably had much to do with the modification and
extinction, especially of the higher mammalian species."

An equally interesting phase of the subject is given by
the same geologist, who describes Lake Mono, "a body of
intensely alkaline water" at the base of the eastern slope
of the Sierra Nevada. In rowing over to two islands that
rise in it he says: "The water over which we pass gives
the fingers a slippery feeling; if we taste it we find that it
is intensely alkaline and bitter. As we look down into the
water we see that it is clear and limpid, but the view is
usually obstructed by countless numbers of brine shrimps
{Artemia) and larvae of flies. The larvae are thrown
ashore by the waves in windrows that are frequently a foot
or more deep." We might add to the above that were such
to be suddenly covered by a volcanic layer of dust, this on
hardening would present exactly the type of rock, and the
group of organisms, that Rupert Jones repeatedly refers
to in his monograph on the Phyllopoda.

The celebrated eruption of Krakatoa in 1883 was so
carefully noted by many observers, and the results were so
accurately correlated and recorded by Verbeek (20) ;
and by the special committee of the Royal Society {21;
passim), that many lessons of great value in the present
inquiry can be gathered.

As to the origin of the enormous amount of dust ejected,
and which in varying grades of fineness spread over the
atmosphere of nearly the whole world, Judd gives a graphic
description thus: "the great bulk of the volcanic dust of
Krakatoa was undoubtedly formed by the striking together

44

Evolution and Distribution of Fishes

of fragments of pumice, as they were violently ejected from
the crater and fell back again into it. The noise made by
this hurtling of fragments in the air was remarked upon
by several observers, and as I have myself noticed at Strom-
boli, is often more striking than the sound of the ex-
plosions. The action of this "dust making" mill, as an
active volcano undoubtedly is, was well illustrated by the
Vesuvian eruption of 1822. Mr. Scrope, who was an eye
witness of that eruption, describes how day after day, as
the eruption proceeded, the dust particles became finer and
finer, till at last they were able to penetrate the finest cracks,
finding their way into and filling all locked boxes, drawers
and similar receptacles."

As to its composition Verbeek secured samples, the
chemical composition of three of which are subjoined. Says
he: "I have in each case rejected the volatile matters and
calculated the total to 100."

B. Dust which fell

C. Dust which fell

A. Dust which fell

at points within 100

nearly 900 miles

at Krakatoa.

miles from the

from the

Collected by Captain

volcano.

volcano.

Fergenaar Buitenzorg

Buitenzorg.

S. Barbarossa.

Anal.

Anal.

Anal.

Prof. Winkler

Prof. C. Winkler

A. Schwager

Silica

6T.36

66.77

68.99

Titanic acid

J.I2

0.67

0.39

Alumina

17.77

16.44

15.24

Ferric oxide

4-39

341

0.28

Ferrous oxide ....

1.71

1-37

3-72

Manganous oxide-.

.41

.38

trace

Lime

3-45

2.90

2.76

Magnesia

2.32

1.67

0.83

Potash

2.51

2.25

3.47

Soda

4.98

4..14

4-32

The amount of dust discharged must have been enorm-
ous. Thus at the climax period on August 27th "on board
three vessels the pumice dust fell on deck" in such quanti-
ties as to employ the crews for hours in shovelling it from
the decks, and in beating it from the sails and rigging. On
board the "G. G. Loudon," anchored in Lampong Bay, it

Related Geological Conditions 45

is recorded that after the rain of pumice stone in the early
morning, only dust and water fell in the form of mud, which
accumulated on deck at the rate of six inches in ten minutes.

But it is observed that the discharge was probably much
less than that from other volcanoes in historic times, for
that "of 1783, and of Tomboro, in Sumbawa in 18 15, were
all accompanied by the extrusion of much larger quantities
of material than that thrown out of Krakatoa in i883«"

As to the total quantity of dust ejected, and the distance
to which this was carried, the results unfortunately from
the geological standpoint are meagre and conflicting. From
the reports of persons on board vessels in various parts
of the ocean, and from those of persons at various points of
land Verbeek has reached conclusions of approximate value.
But Archibald {21; 448) comments thus on these: "If
we suppose that the area represented by these ships alone"
(dealt with in the report) "was 1,100,000 sq. miles, and
was covered uniformly to a depth of only 5 millimeters or
0.02 inch with dust, we should find for the total amount
which thus fell 14.4 cubic kilometres (3^ cubic miles) an
amount not much less than that calculated by Mr. Verbeek
for the total amount of materials of all kinds ejected. It
appears then that the finer dust, which was transported
to more than 2000 English miles from the volcano toward
the west alone, might have equalled in amount what fell in
its immediate vicinity; and it seems quite possible that as
large or even larger a quantity was blown into such minute
particles as to be capable of remaining in the highest regions
of the atmosphere, and being carried right around the world
in the tropical zone within a few days after the eruption."

From the mineralogical, the geological, and not least
for our present purpose from the palaeontological stand-
points, some comparative analyses made by Retgers at the
Buitenzorg station are highly suggestive, as are the com-
ments by Judd on these. He separated the glassy or
vitreous particles from the crystalline, and also the several
mineralogical varieties of the latter — the felspar, the en-
statite, the augite and the magnetite — from each other,
with the following results:

46

Evolution and Distribution of Fishes

S.'fl

«£

c

CO

X
» ...
3lN

2.S

Silica

Titanic acid

Alumina

Ferric oxide 1 .
Ferrous oxide j .
Manganous oxide

Lime

Magnesia

Soda

Potash

68.12
o.i8

15.81
5.01

3.78
1. 18
5.09
1.06

58.29
27.19

8.27

5.82
1.22

52.3

6.1

27.7

trace

2.2

13.6

48.6

8.2

14.0

18.9
11.6

6.7
56.0

99-23

100.79

101.9

101.3

In connection with such results Judd refers to the vary-
ing composition of the dust at different distances from the
centre of ejection and says that samples were taken "from
many points, ranging from 40 to 1,100 English miles away
from the volcano." Those nearest the volcano showed
"greater abundance in them of fragments of crystals, es-
pecially those of magnetite and other dark colored minerals.
Those dusts which were collected at the greatest distance
from the volcano were excessively fine and almost perfectly
white in color."

The above exactly explains the varying aspect, composi-
tion, and consistency of many rock-strata occurring in all
formations from the Silurian upward, and which are usually
rich in the most finely preserved fossil remains. Judd's
conclusions are as follows: "Of the immense mass of com-
minuted matter thrown into the air 9/10 of this material
consisted of glass having a specific gravity of less than 2.3,
drawn out into fine threads and thin plates, often hollow
and containing bubbles of air, and sometimes in all prob-
ability reduced to particles of ultra-microscopic dimensions.
These particles of glass would tend to float by the adhesion
between them and air, and in the higher and rarer portion
of the atmosphere their suspension may not improbably

Related Geological Conditions 47

have been aided by their mutual repulsion resulting from
a highly electrified condition."

"The crystalline particles in the mass would consist
of fragments of felspar, with a specific gravity ranging
from 2.54 to 2.75, of fragments of pyroxene with densities
of 3.3 to 2-5^ and of magnetite, with a density of 5.0. The
crystals of felspar, hypersthene, and augite were, in the
original pumice, of much greater size than the magnetite.
But the easy double cleavage in the felspar, and to a smaller
extent in the pyroxenes, would facilitate the reduction of
these minerals to finer particles than the magnetite."

As the particles travelled outwards from the centre,
they would tend to fall, therefore, in the following order: —
(i) magnetite (the heaviest and least friable material);
(2) pyroxenes (next in weight and only moderately cleav-
able) ; (3) felspar (lighter and very cleavable) ; and (4)
and last, the very light and friable glass."

"At all points therefore the dust which fell would have
a tendency to differ in composition from the pumice out
of which it was formed. Near the volcano the abundance
of the crystalline materials falling, and especially of the
magnetite and the pyroxenes, would render the dust darker
in color and more basic in composition; while farther away
the glass and felspar particles which fell, would have a
smaller admixture of the more basic materials. A certain
proportion of the glass, including the ultramicroscopical,
the elongated and the very thin particles would float almost
indefinitely and would not find any place in the masses of
dust collected around the volcano."

The number of active or recently extinct volcanoes
throughout the world has been estimated by Judd as ap-
proximately 1000. But the relative thinness and plasticity
of the crust during palaeozoic times, must have favored a
much larger number, and such is consonant with the rock
record. Even in Mesozoic and Coenozoic times pronounced
activity is indicated, though the volcano-rents themselves
have often been obliterated. Furthermore, while the act-
ivity has mainly been exhibited from the cones or higher
points of land areas, it must frequently have been sub-
marine, and productive of destructive tidal waves.

48 Evolution and Distribution of Fishes

It seems possible, therefore, that by invoking the aid
of such agencies, the origin, structure, and richly fossilifer-
ous nature of many bone beds, fish beds, and related strata
can be explained, for where multitudes of entire fishes are
preserved as perfectly as in a museum, the volcanic dust
probably fell as these were being destroyed by mechanical
concussion, by poisonous gases, or by super-heated waters,
possibly even through clogging with dust of the gills. If
such destruction occurred — as we hope to show actually did
happen in fresh-water lakes or swamps, or in shallow seas
whose bottoms became elevated either during death of the
fishes or soon after, the continued fall of dust would im-
mediately cover and seal them up. As the oily constituents
of the fishes exuded, and as increased pressure of the ashy
material took place, simultaneously with drying of the
dust deposits in the sun, the oil would aid in preservation
if sufficiently rich, while the deposits of ash, gradually
hardening by chemical action and reaction as above de-
scribed, would render permanent the preservation process.

Where, as in the Downton deposits of England and the
Corniferous deposits of America, an intermingled mass
of teeth, scales, spines or jaws mainly make up the "bone-
bed," the soft dead bodies of great shoals of fishes killed in
some sudden manner as above described, had undergone con-
siderable decay in some shallow, freshwater lagoon. While
decay of the flesh took place an abundant discharge of oily
constitutents occurred, the harder parts became separated
and dropped into the volcanic ash, where they were, by
pressure and chemical action, condensed into a solid mass.
The discharged oily materials receive consideration below.

Such an explanation seems to afford a complete key to
many hard fissile beds of Old Red Sandstone. Thus those
described by Flett {22; 383) in the Orkney Isles and by a
A. Geikie (2j; 399) for Dunnet Head, are cases in point.
Though we would not press the matter unduly at this stage,
it even affords a likely reason for the origin of many beds
of ironstone, that in the States, in Canada, and in various
parts of Europe, are so often encountered in sections of
Old Red and of Carboniferous age, not to say in later
deposits. The often abundant embedded or interlaminated

Related Geological Conditions 49

remains of fishes, eurypterids, and molluscs of freshwater
habitat in such ironstones are a noteworthy feature.

VII. Petroleum and its probable relation to fishes.

Another highly important geological phenomenon, that
we hope to show is intimately connected with the life, death
and fossilization of fishes, can now be taken up. Through-
out many parts of the world, and at times on gigantic scale,
reservoirs of natural oil, of petroleum, of gas and of
asphalt have been discovered, and today constitute highly
important commercial products.

From the upper Silurian rocks, upward to comparatively
recent Tertiary formations, rich deposits of these have been
tapped and extensively utilized. But the question of the
possible source and mode of formation of such bituminous
deposits, has called forth a wide variety of views. These
views have been synopsized by Engler and Hofer (2^:11,
passim), also by Redwood (25; I, 268-283). An inorganic
and an organic source haVe alike been claimed. The former
we will not further discuss, since we regard the extremely
varied products of petroleum as without an approach or
parallel, in any synthetic action effected through expenditure
of inorganic energies, but as being exactly such as might
be called "end-products" of destructive analysis amongst
plants and animals. But some advocates of the "organic"
theory of origin have suggested that petroleum and its
products represent decomposed plant substances, produced
either from accumulation of resin and allied hydro-carbons
formed by trees, or from decomposition — possibly under
heat and pressure — of vegetable fats and fixed oils de-
veloped in the tissues.

Now at the present day the tissues of many Hepaticae
or scale-mosses and of the true mosses, also the spores of
club mosses are rich in fixed oils. But though we would not
deny origin of a very limited amount thus, the total pos-
sible accumulations of these or of resinous hydrocarbons,
seem wholly insufficient to explain the huge — almost inex-
haustible — supplies of petroleum throughout the world.

If we turn now to the animal world, most groups of
animals contain supplies of a fatty nature. But to explain

50 Evolution and Distribution of Fishes

requisite conditions from an animal source one must almost
of necessity postulate: (a) the existence throughout the
entire geological record from the Silurian upward of a most
prolific type of organism; (b) the production in such of
a substance or substances that would directly, or by decom-
position-change, give rise to petroleum and its products;

(c) the comparatively sudden destruction on an extensive
scale of great masses of the organism, and the accumu-
lation of these masses in special pockets or layers of strata;

(d) the comparatively rapid decay of the accumulated or-
ganic masses in freshwater or possibly in salt water, and the
setting free of the more stable oil from the rapidly de-
composing albumen products; (e) the gradual absorption
of this oil into some stratum of highly pervious nature;
(f ) the nearby presence of lower and upper impervious beds
that would bottle up and conserve the oil; (g) the sub-
sequent anticlinal — more rarely synclinal — uptilting of
the entire rock mass, and its exposure to frictional, volcanic
or other source of heat; (h) the' resulting splitting up of
the accumulated oils, under pressure and fairly high tem-
perature into petroleum products.

While we would not deny that in some cases and only
to a very small extent other groups of animals than fishes
have contributed, and probably did contribute, to this out-
come, the writer would strongly afl'irm — from all the evi-
dence to hand — that fishes formed the source of supply to
a preponderating extent. Further, all of the above require-
ments are fulfilled when we follow out the geological
records of fishes. Thus many palaeontologists have often
commented on the oily aspect of the matrix in which fish
remains occurred from the time of the Devonian onward.
And this applied, not to one or a few species, but to
many, distributed over the successive periods.

Murchison early drew attention to the possible origin
of bituminous rocks in the following words (26:542):
"The Flagstones of Caithness, which were first described
by me In the year 1827 under the name of 'Bituminous
Schists' (Trans. Geol.Soc.s 2, v. 2 (1827)213) are in many
places Impregnated with bitumen, chiefly resulting from the
vast quantity of fishes embedded in them. Their most dur-

Related Geological Conditions 51

able and best qualities as flagstones, are derived from an
admixture of this bitumen with finely laminated siliceous,
calcareous and argillaceous particles, the whole forming
a natural cement more impervious to moisture than any
stone with which I am acquainted." He then subjoins
analyses and valuable observations on the nature of the
rocks.

Again in 1829 Murchison, in noting the abundance of
fossil fishes in the oil shales of Seefeld in the Tyrol {28:
139) suggested "the probability of so many fishes having
materiallv cooperated in bituminization of the schist." This
view has been repeatedly seconded since.

But at the present day many fishes like the salmon and
barramunda of freshwaters, also the sardine, anchovy and
specially the menhaden (pogie or mossbunker)of saltwaters
are rich in oils. Our knowledge of the last fish is probably
most detailed and exact, thanks to the studies of Brown
Goode (2^:180). He has shown that a gallon of oil is
yielded by 100 to 250 animals, according to the lean or
fat state of these at different periods of the year. Each
animal is on the average 12 inches long, weighs 11 ozs.
and attains full size in about four years. As many as
15,000,000 of them have been taken in a limited area
by one company in a season. So were one gallon of oil
yielded by 150 fish, the above season's catch would repre-
sent 100,000 gallons of oil.

But more striking is an estimate by Goode, who reckons
"the total number destroyed annually on our coast by pre-
daceous animals at a million of millions," and again he
gives {2g: 109) "three thousand.millions of millions (3,000-
000,000,000,000,000)." Now it seems a conservative esti-
mate if we consider that the closely jumbled together teeth,
bones, and fin-spines of many Silurian, Devonian, and more
recent bone-beds, that cover thousands of square miles of
area in many cases, represent an even greater and more
widespread destruction of fish-life than that wrought within
a year by predaceous animals for the menhaden. If then
we accept that a gallon of oil was yielded by 200 fish, the
yield would represent five quadrillions of gallons of oil.

52 Evolution and Distribution of Fishes

If we compare this with the total production of oil
from the oil fields of Pennsylvania and New York up to
January, 1885, this amounted only to 26,000,000 barrels
of forty-two gallons, or one billion, ninety-two million gal-
lons in all. Sterry Hunt in calculating the oil contents of
the petroliferous dolomite of Chicago estimated "its petro-
leum content at one-tenth of one per cent, and the thick-
ness of the stratum at 500 feet, both of which figures are
probably within the limits." He accordingly estimated
"the petroleum contained in it to be more than 2,500,000
barrels to the square mile." Both of the above figures —
enormous though they may seem — fall far short of the
probable destruction of menhaden during any one year.
Now the total production of crude petroleum from all of
the oil fields of the world, up to 1914, was 5,593,262,936
barrels of 42 gallons, or a total of 234,917,043,312 gal-
lons (The American Petrol. Indust. (1916)258-59). If
we again accept it that 200 fishes are required to yield one
gallon of oil this would involve the sudden destruction of
only 47 trillions of fish, or the one twenty-thousandth part
of the number of menhaden estimated to be preyed on and
destroyed in a year. But, as will be frequently noted in
later pages, some of the fossil fishes that are surrounded by
zones of bituminous material in the different formations,
are only one-half to one-third the size of average men-
haden. On the other hand a considerable number of spec-
ies, notably those of the freshwater Pennsylvanian-New
York shales (pp- 134-35)? of the freshwater Solenhofen-
Bugey shales (p. 195), and of the marine Kansas-Texas
shales (p. 223-24) are equal to or larger than the menhaden.
So the above calculations can well stand as at least an ap-
proximately fair estimate of the average fish-yield.

The world's production of petroleum, however, is at
present drawn from nearly every one of the geologic for-
mations, from the Silurian upward. Now in any one of
the many bituminous horizons listed, the wholesale destruc-
tion of fish-life must have been truly cataclysmic and wide-
spread. Furthermore, and contrary to past reasonings of
most geologists If we except those of Russell and one or two
others, the most celebrated fish-strata have their enclosed

Related Geological Conditions 53

organisms so perfectly preserved In the death attitude, (Fig.
I ) that seahng up and preservation of the organisms must

Fig. I. Slab of rock with specimens of Bothriolepis from
Miguasha, New Brunswick, laid bare with many others by Prof.
Patten. Note headed direction of the animals. (After Patten).

have been effected wholesale, and oftento a depth of several
inches or even feet within a few days at most. Otherwise,
and had the period been more extended, disintegration of
the fish, escape of the oily products, and the breaking up
of the skeleton would inevitably have resulted. Such actual-
ly seems to have been the case where "bone-beds" were
formed.

As to the actual quantity of fish that had perished, and
of oil obtainable from rock strata, many "bone-beds" can
be continuously traced over hundreds of miles in America,
in Britain, and over the European continent. This also
in rocks belonging to nearly every one of the great forma-
tions. From many indications even, suggested by the
stratigraphic, the lithologic, the palaeontologic, and geo-
chemic standpoints, the writer would not be surprised to
learn in time that some of these bone-beds have a lineal
continuity for a thousand to fifteen hundred miles.

54 Evolution and Distribution of Fishes

As not a few geologists have already suggested, the
contents of each of these bone-beds must have represented
the sudden death and decomposition of as great an accum-
ulation of fishes as Goode has indicated above for destruc-
tion of the menhaden by its enemies in a year. But since
the rock, in which such enormous numbers are mainly found,
is often of a hard fissile metallic character, and probably
indicates a sudden volcanic dust deposit formed during
active volcanic changes in the earth's crust, these hosts of
fishes may not only have been killed and entombed, they,
enclosed in the dust stratum may have been upheaved above
the water, exposed to sun-heat and sun-drying, as well as
to volcanic crustal heat, till abundant oils had exuded.

Now when one geologically examines the areas over
the world that are already known to be rich in petroleum,
it appears that the great majority of these are in close con-
tact with, or have an indirect connection with, strata that
abound in fossil fishes. Thus that hitherto richest and most
extensively exploited area that extends from West Virginia
through Western Pennsylvania and eastern Ohio north-
ward through Ontario and Erie to the Great Slave Lake
and Hudson Bay, is the region that has yielded a more
abundant and varied fish-fauna enclosed in rocks of the Old
Red Sandstone or of the Carboniferous age, than any other
part of the world. As described also by J. P. Lesley
for the Old Red and the Carboniferous systems of Penn-
sylvania (jo:II : 1453; III: 1759 : 2565) the numerous
extensive and prolific fish "bone-beds" that are intercalated
between other strata, form a remarkable feature of these
formations as of others described later in this work.

Redwood again points out (25:1:164) that the Upper
and perhaps the Lower Silurian strata of north eastern
North America may yet yield abundant supplies of mineral
gas, if not of petroleum. While such might represent
decomposition products from decay of primitive Silurian
cyclostomatous fishes, it is just possible that the primary
source of this might result from superincumbent strata of
Old Red or Devonian age. Redwood, Engler, and others
have shown that petroleum-yielding strata of every age,
from the Silurian up to the Tertiary period, occur over prac-

Related Geological Conditions 55

tlcally the whole world. While the detailed search for
these has gone forward rapidly, we still desiderate accu-
rate details as to the rocks that contain, or are near to, the
sources of the petroleum. But In many Instances we know
now that these are usually adjacent to beds that are rich
in fossil fish remains.

But the writer now takes exception — as he will repeated-
ly do later — to a statement in Redwood's work (25 : 1 : 280)
and by implication to that of the other two authors cited,
which says regarding the possible origin of petroleum:
"The Engler-Hofer theory, as developed by its authors up
to the present time, states that petroleum is derived from
the natural decomposition in situ of the fatty remains of
marine organisms, both animal and vegetable." Up to
at least the Llassic period, we would distinctly affirm that
nearly all of the petroleum is the decomposition product
of freshwater fishes, and only from late Jurassic or early
Cretaceous times onward do marine fishes seem to have
contributed largely — In some cases perhaps entirely — to its
formation.

That at least some species or even genera of fossil
fish were rich in products of an oily nature, throughout all
of the geologic formations, will be frequently emphasized
in later pages of this work. One of the many exact proofs
is, that often Isolated fossilized fishes are surrounded by
abundant oily products, that give a characteristic aspect and
odor to the enclosing block of rock. Again where masses
of ten to twenty are heaped together in a rock that other-
wise is sparcely fossiliferous, the area around the mass
specially shows an oily horizon.

As to the exact manner In which the fat, oil, or other
more complex constituents of fishes may have contributed
to formation of petroleum. It might first be noted that in
the case of the living Protopterus "the nutrition of the
dormant fish is effected by the absorption of the fat stored
up about the kidnevs and gonads" (2:513). In contrast
to this, of Its ally Lepidosiren^ it has been said: "during
the rainy season the Lepidosiren eats voraciously, and a
reserve of fat Is stored up in the tissues. The great amount
present in the muscular tissues of fresh- and salt-water fishes

S6 Evolution and Distribution of Fishes

already named, is familiar to everyone who has dissected
them."

In view of the prodigious quantities of fishes that must
often have been destroyed wholesale through volcanic
activity (pp. 120, 148) during the Old Red to Triassic per-
iods, it might be expected that more abundant remains of
these would have been preserved in the different rock-
strata of freshwater origin. Thus we have manifold proofs
that Selachians existed in freshwater areas from Devonian
on to Permian days at least, and in the sea also for a
relatively short period during Carboniferous times, but
abundantly from Upper Jurassic and Lower Cretaceous
times onward. But rather scant traces of them are met
with in the fossil state, unless they developed some resisting
parts such as teeth, spines, scales or jaws. Except for
these, and for the very rare and sudden preservation of
them in entire state in the Solenhofen, the Wyoming, and
other hard fine fissile rocks, we would have been unaware
of their existence. The soft and oily tissues as such have
nearly always disappeared.

The above data all point strongly to the conclusion that
petroleum products are mainly due to destructive decom-
position of fish-oils, resulting from wholesale death of fishes
during different geologic periods of the earth's history.
Such widespread destruction seems in nearly every case to
be explainable by direct or indirect volcanic action, such
as poisonous gases, volcanic ashes or scoriae, lava flows,
earth and water concussions, or supramaximal heating of
areas in which fishes lived. But the accumulating petro-
leum products may have been slightly added to by simul-
taneous or later destructive decomposition of vegetable
products. Thus Redwood (25:1:47) says while describ-
ing the Assam oil-fields: "Mr. F. R. Mallet has enum-
erated the districts where oil has been noticed in the dis-
tricts mentioned. Thick soft sandstone is the principal
rock traversed by the drill, but here clay also occurs. The
oil always rises on or near the outcrop of the coal-bearing
group, usually near the outcrop of a seam or seams of
coal. Mr. Mallet records an instance in which the oil
oozes from the coal itself, though as he points out, this

■ Related Geological Conditions 57

may have been merely due to the fact that the coal Is the
last rock through which the oil passed to the surface."

The writer also, when making field studies of the oil-
shales of Midlothian in Scotland, was often impressed by
the presence of flattened impressions of the stems and
branches of Lepidodeiidron, Lepidophloios and JJloden-
droH, side-by-side with those of various species of Calci-
ferous Sandstone fishes, the shale itself being completely
permeated by the bituminous products, that at once began to
"sweat out" when a piece of the shale was heated. Red-
wood gives a valuable and condensed epitome of the argu-
ments for a vegetable and animal origin of the petroleum
on pp. 272-283 of his first volume, and to it the reader is
referred who desires added information.

If it be now asked: What became of the oil, fatty
tissue, or muscles of ancient fishes when these were en-
tombed wholesale, the first suggestive answer was given
In 1867 by the exact chemical investigations of Warren
and Storer (57:121-176). Experimenting with menhaden
oil they converted this into a soap, by blowing steam into
a mixture of lime and the oil. The soap was then strongly
heated, and the distillate obtained was a crude petroleum
oil. By redistillation many of the characteristic hydro-
carbons that are now manufactured from petroleum oil
were obtained, such as amylene, caproylene, benzole, tol-
uol, xylol, isocumole, etc. But a matter of considerable
interest, in relation to the pitch or bituminous strata of
Seefeld, Caithness, and many other places mentioned in
later pages, was "the separation of a sort of tar" (p. 185)
from one of the liquors obtained during the investigation.

It was stated above that a mixture of lime with the
fish oil was treated with steam. Now in the great ma-
jority of cases, bituminous fish beds contain a moderate
to large amount of calcareous material; while volcanic
action seems unquestionably to be associated with the for-
mation of such beds. This again would suggest a possible
superheating of the strata and their enclosed organisms,
some time subsequent to their deposition. Still later, earth
movements and upliftings or foldings, to produce that usual
anticlinal relation of rocks which so often Is characteristic

58 Evolution and Distribution of Fishes

of oil-strata, would also explain the subsequent formation
of secondary products of petroleum decomposition.

Recently Engler has stated from experimental evidence,
that decomposition of animal oil is effected by two stages.
First, owing to bacterial action — and this we claim would
proceed much more rapidly and perfectly in freshwater
than in the sea — nitrogenous matters are eliminated, "the
action being automatically stopped almost as soon as the
fats are attacked." The second stage, clearly demonstrated
by Warren and Storer as well as confirmed by Engler's more
recent results, consists in the combined and continued action
of heat and pressure on the oils, though, according to
Engler, even this may be initiated by oil-splitting bacteria.

The entire subject opens up many avenues for future
observation and experiment, especially in view of the
writer's claim that a freshwater and not a marine habitat
was through long ages typical for fishes.

From all that has been adduced above then the writer
would conclude: (a) that many isolated fishes, or groups
of them in the fossilized state, show rich petroleum prod-
ucts around or within the specimens; (b) that petroleum
oils are usually found only where abundant fish remains
occur; (c) that sudden destruction of fish-life by direct
volcanic agency, and over wide expanses of water has
been recorded, and evidently also took place widely and
violently from late Silurian to Miocene age; (d) that
contrary to past opinion, and as is demonstrated in suc-
ceeding chapters, this took place wholly or almost wholly
in freshwater areas, and only in later Jurassic and succeed-
ing times did such occur in saltwater; (e) that the amount
of destruction and the widespread nature of it, as evidenced
by "bone-beds" of fishes, by bituminous schists, etc., would
amply account for all of the petroleum oil or gas, hitherto
removed by man from any strata; (f) that frequent sudden
entombment and preservation of fossil fishes were effected
by volcanic dust showers which accompanied or succeeded
such destructive agents as poisonous gases, earth and water
concussions, superheating of waters and other means;
(g) that the oils and fats, possibly even degenerate muscu-
lar tissue, set free abundant products from which petroleum

Related Geological Conditions 59

supplies could be obtained; (h) that the varied and exact
experiments of Warren and Storer prove that nearly all
of the crude petroleum, as well as the more typical products
of destructive distillation obtained from it, can be accounted
for as due to decomposition of fish-oils, through heating
of these under pressure, or by some sim'lar expenditure
of energy.

6o Evolution and Distribution of Fishes

CHAPTER III.

THE EVOLUTION OF FISHES FROM
INVERTEBRATES

Numerous views have been advanced to account for
the origin of vertebrate or chordate animals from some
invertebrate stock. These are synopsized in various zoo-
logical textbooks, and need not now concern us. The
writer in his "Causes and Course of Organic Evolution" has
already adduced abundant reasons for accepting the group
Nemertinea as that which most exactly and most continuous-
ly satisfies requirements. Such a view had previously been
strongly advocated by Harting and especially by Hubrecht,
to some extent also by Balfour and Lankester. But all
of these authors dealt only with a few of the organs. In
this chapter the writer will review, and still further advance,
arguments and evidences in favor of this contention.

The group Nemertinea as now existing, is made up of
genera and species, the simpler of which show surprisingly
graded connections with the Turbellaria, as pointed out
by several authors, and synopsized by Burger. In the
most evolved or metanemertean members of the Nemer-
tinea also these exhibit remarkable fundamental agreement
with the simpler chordate animals. All however are soft-
bodied, if we except the styliform teeth, and so far as yet
known have left no fossil remains. But as pointed out
in last chapter, their present geographical distribution com-
pels us to accept that they are a very ancient group. Their
distribution also, might on first thought cause us to conclude
that the group originated along littoral sea areas. For
nearly 450 of the 465 species now known, occur there. But
the wide extension of the nine freshwater and the eight
land species, also their continued persistence in spite of
denundation and geologic changes generally, strongly in-
cline us to favor a freshwater origin for the entire group.

A very strong argument for this is, that in the rhab-
docoel turbellarians — the majority of which are fresh-
water — that important organ the proboscis develops as

Evolution of Fishes from Invertebrates 6i

an outgrowth and backward growth from the dorsal region
of the gullet, so that the mouth and the protrusible probos-
cis open by a common aperture. This condition is retained
in most species of the nemertean sub-group that Burger
has designated the Metanemertini (op. cit. p. 404), and
which includes all of the freshwater and land species, as
well as related marine ones. But since all of the Nemer-
tinea exhibit a common fundamental structure, and as every
fact of evolutionary history warrants the possession by them
of interconnected details, we will not hesitate to compare
details of any species, though laying special emphasis on
the Metanemertini.

In connection with these, and generally treated now
as groups of the Chordata, are the Hemichordata or siphon
worms, the Urochordata or ascidians, and the Cephalochor-
data or lancelets. These will at times be referred to, though
the writer would regard all as derivative phyla that have
branched off from some advanced nemertean line, or from
types intermediate between the nemerteans and the true
fishes.

I. Size and shape.

Metanemerteans may vary from 3 to 500 mm. in length
by y2 to 20 mm. in width. Some species of Drepanophorus
are 400 mm. x 20 mm. Dendy says regarding the land
form Geonemertes atistralis: "as it lies at rest with the
proboscis retracted it has very much the appearance of a slug
or of a small planarian worm, and is very soft and slimy.
When it begins to crawl, which it readily does on being
disturbed, the body elongates, until in large specimens it
measures about 40 mm. in length by 2.5 mm. in greatest
breadth. The anterior extremity is then seen to be rounded
and perhaps slightly swollen into a head, the posterior
extremity tapering gradually to a blunt point where the
anus is situated." The above two types then are about
twenty times longer than broad.

In size and shape Amphioxiis, Myxine, Petromyzon,
and many of the higher fishes show progressive advance
on the above, but frequently retain the same relative length
to breadth, as well as outline.

62 Evolution and Distribution of Fishes

II. Color, While some metanemerteans are gray,
silvery or brownish in color, like many fishes, they often tend
to assume gaudy hues of blue, green, pink, and crimson,
that seem to be protective in value (Burger p. 533) . Similar
tints and degrees of coloration characterize some fishes,
and in both groups the tints are due to pigment-cells em-
bedded in the skin, and which may change in tint with
change of environment.

III. Skin. In metanemerteans this consists of an epi-
dermis that is richly ciliated; in Amphioxus the embryo
only is ciliated, while fishes, so far as known, have lost the
external cilia, but retain these over some internal surfaces.

Glands, embedded in the epidermis, and resulting from
modification of Its cells, are very abundant amongst nemer-
teans. They may be single or arranged in packets, and
vary from elongate-tubular to ovate In shape. These main-
ly secrete the abundant mucus that surrounds the skin, but
may also exude a somewhat granular substance, and even
pigment materials. In Cyclostomata many goblet-shaped
cells excrete a very abundant mucus, that may even more
completely envelop each animal than In the last group. In
other fishes mucous excretions from epidermal gland-cells,
are usual, the amount of excretion reaching its climax In
the dipnoans, where as In some land nemerteans, a special
overflow may at times be changed Into a cocoon ( J2 : 201),
as shown by Parker for Protopterus.

Thread cells or stinging cells occur in the epidermis
of some Nemerteans (e.g. Linens, Burger, p. 50), but
these are often restricted to the epidermal cells of the
proboscis as in Macriira and Cerehratuhis (Burger p. 212).
In cyclostomes the myxinoids are provided with urticating
cells that In structure and mode of action resemble those
of nemerteans. Some epidermal cells of young lampreys
secrete a digestive ferment, and such may represent modi-
fied urticating glands. Poison glands are found in not a
few fishes, but usually associated with surface spines
through which the poison Is excreted. The group of Weever
fishes (Trachinus) Is an example.

Evolution of Fishes from Invertebrates 63

Dermal plates or scales. Such structural details call for
special emphasis, since they suggest a parting of the way
amongst ancient nemerteans, that led on the one hand to the
soft-bodied cyclostomes, and on the other to the tubercled
and later to the plated or scaled fishes. While most nemer-
teans remain soft in their surface tissues, others — e.g., spe-
cies of Eunemertes, Cephalothrix, Tetrastemma and Geo-
nemertes — may secrete glistening oval, angular, or hook-
like masses of a crystalline nature, and which are mainly
composed of carbonate of lime {^^ : 67 ; S4'- 43° 5 35'- I045
^6:^6). These cells are often in direct contact with
others which are glandular, and so the entire morpho-
logical foundation exists here for further evolution of such
isolated placoid granules or spines as characterize the
primitive genera of fishes, Thelodus and Lanarkia, of
Silurian and Devonian strata. From these again to the
placoid or ganoid scales of fishes the gradation is easy.

Closely related to such secretions amongst the
metanemerteans, and originating from the middle part of
the invaginated epidermis that forms the substance of the
proboscis, are the horny stylets that project as offensive
organs when the proboscis is extruded (Fig. 5). These
arise in succession from cells or groups of cells present in the
mid-region of the proboscis when seen at rest. Structurally
they suggest a very appropriate starting point for forma-
tion of horny vertebrate teeth, and this in a way that will
be more fully explained in a later section. As described
by Montgomery and by Bijrger (op.cit. 227-29) they origi-
nate as a secretion of the modified epidermal cells of the
mid-proboscis, and consist of two to five distinct and con-
centric layers of tooth substance, the outermost of which
has a shining structureless aspect.

In various genera then of the Metanemerteans two epi-
dermal formations arise: (i) calcareous epidermal secre-
tions that form alongside glandular epidermal cells; and
(2) the horny proboscis teeth or stylets that undergo
steady wear and renewal. The former, by increasing com-
plexity in structure and by increased activity of the related
epidermal cells, would start formation of the tubercles,
spines, and ultimately the elaborate plates and scales that

64 Evolution and Distribution of Fishes

are so typical of the main groups of fishes. The latter, by
increasing specialization in development, and condensing
modification of the front part of the proboscis, would form
the horny to calcareous teeth of the buccal region in cyclos-
tomes and higher fishes.

So from some primitively related genera of metanemer-
teans, that had all early developed proboscidial stylet
teeth, which later became buccal or pharyngeal teeth, we
would trace two divergent lines of evolution. One of these,
remaining soft-bodied in its epidermis, pursued one path-
way of progress that led to the cyclostomes and later to
primitive ancestors of the caecilian amphibians. The other,
by secretion of horny and calcareous tubercles, led up to
Thelodus, Cladoselache and still higher types that made
up the main line of piscine development. But that the
calcified tubercles, the stylet teeth, and the buccal teeth
represent practically identical formations has been already
emphasized by Bridge (5(5:247-48) and others.

IV. Sense-organs of the Head.

These are (a) the frontal sense-organ of nemerteans
which we have correlated (/: 428) with the olfactory sense
organ of fishes; (b) the eyes or optic sense-organs; and (c)
the auditory sense-organs.

(a) The frontal or olfactory sense-organ. In metane-
merteans, at the front end of the head, a small orifice opens
into a saccular depression that is lined with ciliated cells,
and is surrounded internally by an investment of muscular
tissue. The organ is innervated by a branch from the
anterior part of the dorsal ganglion. Above this frontal
organ lie clusters of glandular cells — the so-called "head-
glands" — and often the orifices of these open into the organ.
Burger has named this the taste organ. ' In Cerebratuhis
three such organs — one median and two lateral paired
ones — occur and show similar structure. From their posi-
tion, structure, early embryonic origin (<5:373), nerve
supply, and relation to the head-glands above, the writer
views such as an unpaired or paired {Cerebratuhis) ol-
factory organ. In Amphioxiis the olfactory organ is like-
wise a single saccular depression lined with ciliated cells.

Evolution of Fishes from Invertebrates 65

and is further innervated by "an antero-dorsal hollow out-
growth from the brain." In Cyclostomes the olfactory
organ is similarly unpaired in the embryonic state and re-
mains so in the hag-fishes; but in the lampreys as adult
life is reached a vertical median septum divides the organ
into halves, and these are supplied by two olfactory nerves
from the brain. In gnathostome fishes two distinct and
paired olfactory organs, that are innervated by two ol-
factory nerves, are present. In many teleosts an evident
homologue to the head glands of metanemerteans is seen
in the glandular "nasal sacs," which similarly are back-
ward and dorsal prolongations from each nasal organ.

(b) The eyes or optic organs. In metanemerteans
these show great variation, alike as to number, paired or
median position, complexity of structure, and function.
Even in one genus, like Geonemertes^ they may vary from
the most common number four, to as many as thirty or
forty (55: no). At times the anterior of the four usually
present are paired with each other and are well developed,
while the posterior pair may be smaller, more or less ap-
proximated, and even placed in submedian position with
each other. This anticipates and resembles the parietal
and pineal eyes of the cyclostomes and higher fishes. In
structure they show all of the fundamental parts that
characterize fishes and higher vertebrates. In position
they lie above and in front of the brain.

(c) The auditory organs. In the great majority of
metanemerteans paired structures open along the postero-
lateral part of the head and have been termed the cerebral
organs. In 19 14 the writer drew attention to their struc-
tural similarity to the embryonic ear of vertebrates
(7:429). They attain their highest development in
meta- and hetero-nemerteans, where they appear as
swellings behind or beside the front part of the dorsal brain-
lobes. They open by small external pores along the sides
of the head, and at the bottom of the head-grooves. In
cyclostomes and elasmobranchs the orifice of the ear in the
embryo is in line with the first inpouching of the branchial
system, and so occupies the same position as in nemerteans,
since the writer regards the head-grooves and the first

66 Evolution and Distribution of Fishes

branchial pouches as homologues. The external ear-orifices
remain open in both of the above groups, and so this condi-
tion forms another point of contact with nemerteans. But
the positions of the orifices become gradually shifted till
ultimately they open on the latero-dorsal or dorsal surface,
(d) Epidermal haiis. The only other external char-
acter that deserves notice here is the hair. This seems to
be one of the most primitive, as it is the most persistent
epidermal sense modification of animals. For the "bors-
tcn," "geiselhaare," "haftpapillen," and "hacken" of the
rhabdocoels ( J7 : 2012-2030) are all varieties of tactile epi-
dermal cells. Such persist among the nemerteans as sens-
ory hairs, that Montgomery as well as other authors fre-
quently refer to. In the metanemerteans he describes them
on the posterior part of the body, on anterior and posterior
parts alike, or in somewhat diffuse manner {38: i). Re-
garding fishes Bridge says {36'. 383) "the most remarkable
and certainly the most characteristic of the sense-organs of
Cyclostomes and Fishes are bud-like groups of epidermic
cells in relation with the ends of sensory nerve fibres. Each
consists of a central core of sensory cells, provided with
terminal cuticular sensory hairs, and surrounded by a zone
of supporting and mucus-secreting cells which leave the
hairs exposed at the apex of the bud." He then describes
the two varieties known as "end-buds" and "nerve-emin-
ences. "^

V. The mouth.

In all freshwater and land nemerteans the mouth is a
small subterminal orifice that opens into a pharynx or
buccal cavity of varying size. This is a common cavity
that shows on its inner ventral aspect the small opening of
the gullet, and behind this a more or less circular ridge
that is the attaching edge of the proboscis to the proboscis-
sheath. This ridge we will call, for a reason that will
appear presently, the velum. It bounds the anterior part
or orifice of the proboscis, and so demarcates also the front
edge of the proboscis-sheath (Fig. 2m. p.) from the
buccal cavity. Glandular cells are embedded in its surround-
ing tissue, and evidently pour their secretion into its cavity.

Evolution of Fishes from Invertebrates 67

Fig. 2. Long. sect, head region of Geonemertes austraVts, m,
mouth ; co, common opening of mouth and proboscis tube ; m.p.
velum; d.c, v.c, dorsal and ventral brain masses; c.gl, cephalic
gland ; oes, i, 2, 3 anterior, mid, and posterior oesophageal areas,
the dark area of the mid-oesophagus is highly glandular, and seems
at least in part to be the primitive rudiment of the thyroid gland;
d. gut, intestinal diverticulum or probable hepatic process; ep.
epidermis; cm, l.m, circular and longit. muscle masses; d.gl, dorsal
glands; ps. muscular proboscis tissue. (Reduced from Dendy).

A like description would apply to the mouth and buccal
region of Cyclostomata and other fishes. But the velum
or membrane deserves more detailed consideration. This
has been accepted above as the bounding edge of the united
proboscis and proboscis sheath of higher nemerteans.
Now if, as traced below, the proboscis becomes greatly
shortened, and at least in its hinder part converted into
the pituitary body or hypophysis of cvclostomes and other
fishes, at the same time that the proboscis-sheath becomes
the notochord, the velum would be a ridge or expanse in
front of the point where the notochord ends and the up-
curved pituitary body joins the infundibulum. Such is ex-
actly the relation as indicated by the subjoined figure (Fig.
3) when supplemented by others, given by Dohrn (Camb.
Zool. 391). Alike in Amphioxus, in Cyclostomes, and in
higher fishes, it can be traced, at times prolonged into lobes
or at times becoming richly vascular lateral thickenings, as
in the Dipnoi. Morphologically, as well as phylogenetical-
ly, therefore, the velum is a very persistent and important
demarcating ridge.

68

Evolution and Distribution of Fishes

Fig. 3. Vertical section of young larva of Lamprey {Petromy-
zon) showing notochord, ch, mouth, 0, velum, i^, developing
thyroid gland, //, that is the probable homologue of the glandular
mid-oesophagus of Metanemerteans, and of the endostyle in primitive
vertebrates.

Oesophagus. The small orifice of the gullet in higher
nemerteans leads into the oseophagus, which in some land
nemerteans shows division into three parts, an anterior
narrow tube, an enlarged highly glandular mid-area, and a
more constricted slightly glandular posterior part. But
the mid-area is not merely glandular, some if not all of its
cells are "very richly ciliated." It would thus exactly cor-
respond in requirements to a primitive and diffuse condition
of the endostyle in ascidians, to the hypopharyngeal groove
of Amph'wxus, and to the thyroid gland of fishes, as well
as of higher vertebrates. In the description by von Graff
(5^:430) and Dendy {35'- 92)) ^^ is not determined
whether the cells are in part glandular in part ciliate, or
as possibly may be the case are both conjoined. Burger's
descriptions {6: 198-99) and figures indicate that there are
distinct ciliate and glandular cells but either condition
would furnish the basis for gradual differentiation and re-
striction of the cells to the ventral surface of the oesopha-
gus, to in part a glandular In part a ciliate state, to the con-
densing of these into four longitudinal tracts, and thus to
formation of the endostyle or hypopharyngeal groove
(Fig. 4.gl) of the primitive chordate types Ascidia and
Amphioxus.

Now while In the larva of Petromyzon It remains an
open groove, It later becomes closed, "highly complicated,
with paired anterior and posterior horns and a median
spiral portion," eventually in the adult "the organ is partly

Evolution of Fishes from Invertebrates 69

end.l.-.

Fig. 4a.

Fig. 4b.

Fig. 4a. Transverse section of anterior ventral part of ali-
mentary canal — or branchial sac — of Ascidia mentula, showing cili-
ated depression or endostyle (end . i) with four longitudinal patches
of glandular mucus secreting cells (gl). Below is a blood sinus
(v. bl. s). (After Herdman).

Fig. 4b. Like section of Amphioxus showing endostyle (e)
with four glandular tracts (gl) that secret mucus; m.b.a, blood ves-
sel; sk, skeletal plates. (After Lankester).

absorbed and partly divided up Into a series of glandular
follicles, and eventually forms the thyroid body."' As de-
scribed by Newton Parker ( J2 : 173) in Protopterus there
is a close resemblance, between the thyroid In it, and the
meso-oesophagus In Metanemerteans; and this gives added
value to Kerr's contention that the Dipnoi are an ancient
and likewise a primitive group, which retains many simple
ancestral conditions. The descriptions and figures of
Dendy suggest four paired glandular ciliated and columnar-
celled lobes that occupy the mid-ventral head region In
Geonemertes australis. A more detailed study of the meso-
oesophagus In freshwater and In land nemerteans is how-
ever highly desirable, as thus presenting the probable dif-
fuse beginnings of the vertebrate thyroid organ.

VI. Respiratory system.

At this juncture It may be appropriate to study the
primitive beginnings of the respiratory system. The writer

70 Evolution and Distribution of Fishes

has already drawn attention ( / : 445 ) to the prob-
able origin of the first gill-cleft, spiracular cleft, or hyoman-
dibular cleft, as it has been variously called. He showed
that from the two ciliated depressions of some turbellarians,
to the two ciliated furrows of nemerteans, and thence to
the ciliated branchial cavities of a cyclostome, the series is
a progressive one. But in nemerteans the ciliated furrows
externally are continued into two depressions — one on
either side of the head — that are placed behind the velum,
and come into close contact with the oesophagus, while
anteriorly they give rise to the sacs above treated of and
which the writer regards as the rudiments of the chordate
auditory organs.

Neglecting the latter meanwhile, the two former regions
are In position alongside alike the anterior oesophageal
wall and dilatations or even plexuses of blood-vessels
formed at the anterior end of the three main blood-vessels.
Here then are all the connections and structures for forma-
tion of the first pair of branchial orifices and pouches in
cyclostomes. For by fusion of the adjacent tissues of the
oesophageal wall, of blood vessels, and of the furrows,
currents of water could be established through the mouth,
gullet, preoesophagus, and furrows to the exterior. In serial
succession a formation of additional canals and internal
dilatations could arise, seeing that abundant vascular loops
occur in some nemerteans, close behind the anterior system
already described. Such a development is foreshadowed
in Stichostemma eilhardi {38: i), that is referred to later.
A series of respiratory orifices then, along either side of
the preoesophagus and mesooesophagus, and in communica-
tion with such a rich set of vascular loops as is shown by
the above-named animal, would form a basis for origin
of the respiratory system in fishes.

Two distinct types also seem to have originated. In
one of these fifteen to possibly twenty pairs of external and
internal orifices were formed, with pouch-like respiratory
enlargements between, that were embedded in the meso-
blastic substance of the perioesophageal region. This type
must have characterized the primitive ancestors of the
Cyclostomata, for in species of Bdellostoma fourteen to

Evolution of Fishes from Invertebrates 71

ten, to seven, and even to six pairs are now traced, evidently
in a steadily condensing and reducing series. In the second
type a series of seven (possibly more), to six, to four cleft-
fissures seem to have originated in the perioesophageal
region, from the oesophagus outward. This became the
forerunner of the plan shown in the gnathostome series of
fishes with their gill arches and gill filaments.

The gut or post-oesophageal tract may either be a
simple straight tube, or frequently in metanemerteans it
may be expanded into irregular swellings or even into
paired lobes (55:93). In this manner the digestive and
especially the absorptive surface is increased. The same
result is secured in many fishes by formation of the spiral
valve.

VII. The liver.

The progressive continuity in evolution of the liver
from nemerteans to fishes is we believe admirably illustrat-
ed. In simpler metanemerteans there seems to be no special
appendage to the gut. But in Geonemertes Dendy says :
"just where it joins the oesophagus the gut gives off as usual,
a characteristic diverticulum which runs forward beneath
the last portion of the oesophagus and ends blindly."
Sections of this structure are seen in figure 2. But while
Dendy states as above, his figure might suggest that it origi-
nated from and emptied into any part of the "gut" region.
A more minute study of it is desirable. In Amphioxus
a like position, relation and development occur. "In
Petromyzon, Lepidosteus, and a few teleosts the liver re-
mains unilobed" also. But even in myxinoids and in higher
fishes it becomes a bilobed or trilobed structure that often
attains large size, and may develop an accessory gall-
bladder.

We are still ignorant of the nature of the secretion
in nemerteans and Amphioxus^ but the early origin of this
gland as a primitively simple anterior outgrowth of the
foregut from nemerteans to teleosts is fairly diagnostic.

The termination of the alimentary canal in the anus
agrees in all of the above.

72 Evolution and Distribution of Fishes

Our knowledge of the embryology of freshwater and
land nemerteans is still too imperfect to permit definite
statements as to the formation of mesenteric folds for hang-
ing of the alimentary canal in place, after the manner seen
in vertebrates. But the formation of paired "imaginal
discs.," and the ingrowth in bilateral fashion of the posterior
pair of these in the embryo, recalls the closely similar mode
of formation of the mesoblastic mesenteries in vertebrates.
Burger's statement however, as quoted below (p. 93),
seems to indicate an exact homology.

VIII. The proboscis and proboscis sheath.

From their mode of origin, and their close relation to
the anterior part of the alimentary canal, the proboscis and
the proboscis-sheath or rhynchocoel can next be studied.
This double structure is undoubtedly anticipated and led
up to in the corresponding though simpler structure of the
rhabdocoel turbellarians. The great importance of the
sheath phylogentically consists in its being evidently the
evolving predecessor of the notochord, while the proboscis
evidently becomes modified into the pituitary body, as well
as various buccal structures; a very brilliant generalization
this, for which we are mainly indebted to Hubrecht.

Zoologists are agreed that the proboscis represents an
ectodermal invagination or introvert near the anterior head
region. But two different modes of origin might be claimed
for it. Either it is an in-pitting from the buccal region
within and behind the mouth — and this conforms to its
relation in turbellarians, as well as in freshwater, in land,
and in not a few marine nemerteans — ; or it is an invagina-
tion of the anterior cephalic region outside of and above
the mouth, as in many marine nemerteans. The writer has
advocated the former as the true interpretation, for all
transition stages from an intraoral to an extraoral position
can be traced in living marine types, which for many reasons
the writer regards as derivative from freshwater forms.
Figure 2 then would represent the primitive condition.

But with progressive elaboration, elongation, and
sensitivity to environal agents, the inverted structure grad-
ually evolved an inner highly glandular half that could

Evolution of Fishes from Invertebrates 73

be rapidly protruded, within a more external, eversible
and muscular half (Fig, 5), that functions as a sensitive,
tactile and offensive organ. The specially thick and mus-

FiG. 5. Diagram of raetanemertean proboscis as retracted
within (a) or extruded from (b) the proboscis sheath, p.s. The
rim of attachment, r, of the proboscis to its sheath seems to corres-
pond with the velum of vertebrates, ap. anterior protrusible and
muscular part of proboscis; m.p, median muscular stylet area; s,
stylet; g.p, inner glandular part; p.c, proboscis muscle.

cular area, that unites the inner and outer parts of the
tube in metanemerteans, develops the characteristic stylets
already treated of, and that can be steadily renewed as
old ones are worn away. The surface of the external coat
is often abundantly beset with fine glandular papillae. The
entire organ is innervated by an abundant set of circularly
disposed nerve-fibres, that have been minutely described
and figured by von Graff (5.^:430) and his successors.

In contrast to the eversible, muscular, and often
papillose outer tube, the inner is thin-walled, and its surface-
layer consists of richly glandular cells that stain deeply.
So it may shortly be said that the proboscis in metane-
merteans consists of three portions, ( i ) an outer eversible
tube portion, that in Geonemertes and others has highly
muscular walls and papillose surface; (2) a median some-
what swollen and highly fibro-muscular zone in which
develop and are embedded the semicalcareous semicorneous
stylets; (3) the internal thin-walled tube that in the re-
tracted proboscis is in line with the outer, and is con-

74 Evolution and Distribution of Fishes

nected with it by the stylet zone. Its inner surface epi-
thelium is highly glandular.

Hubrecht considered that in transition from nemerteans
to fishes, the entire proboscis became greatly shortened
and condensed, and during embryological development sep-
arated from the front rim of the enclosing sheath or rhyn-
chocoel, then became bent upward posteriorly, and uniting
with a downgrowth of the brain — the infundibulum — be-
came the important glandular tube that is known as the hypo-
physis cerebri or pituitary body {-fi '35^-3 SS) • ^^^ the
writer has suggested what seems a more complete explan-
ation of the evolutionary changes involved (7:420). For
since the proboscis in freshwater and land nemerteans
is an ingrowth of the posterior buccal cavity, the anterior
muscular eversible part, as It underwent steady conden-
sation and shortening in the evolution of primitive fishes,
might gradually fuse with and spread over the buccal
cavity, or stomodoeum. Thus would arise the muscular
buccal area of vertebrates, and specially the powerful suc-
torial disc that is typical of cyclostomes, sturgeons, larval
gar-pike, of some teleosts, also of larval urodele amphibians
and even of mammals. A tendency to the formation of
stylets, and ultimately from them of buccal teeth, might
spread over the entire area. This would account for their
abundance in Petvomyzon, as well as In some of the true
fishes.

The highly muscular mid-proboscis may, on Its ventro-
lateral sides have condensed and grown forward In simple
or in bllobed form as the tongue of cyclostomes, elasmo-
branchs, dipnoans and crossopterygian fishes; while the
stylets may have been replaced by the strong buccal teeth
of Petromyzon or the ventral plates of teeth in higher
fishes. Such a view is decidedly favored also by Dean's
statement {42: 57) that In the cyclostome Bdellostoma the
tongue, which is bllobed and "studded with rows of rasp-
like teeth, may be greatly everted, and then drawn in by
stout tongue muscles." The nerve threads that passed
to and innervated this anterior portion seem grad-
ually to have separated from their posterior roots, and

Evolution of Fishes from Invertebrates 75

these roots then in growing downward would become the
vertebrate infundibulum.

In vertebrate morphology the pecuHar character and
relation of the downgrowth from the thalamencephalon,
known as the infundibulum, has often excited discussion.
Its history seems to be satisfactorily explained in phylo-
genetic continuity from the nemerteans. For Hubrecht
and others have shown that from the cerebral ganglia
two strong nerves run down to, enter, and innervate the
proboscis. In the anterior muscular portion of it, the two
nerves break up into a complex circular and longitudinal
system, that give extreme sensitivity to the entire proboscis,
specially to the anterior portion. Now, as this anterior part
separated, as suggested above, from the innermost or gland-
ular part, the main nerve threads would become more or
less weakened, sundered, and reduced in function, though
they evidently remained in contact with the glandular por-
tion. So we would suggest that the infundibulum represents
the largely abortive remnant pair of proboscis nerves that
still remain in contact with and innervate the pituitary
body. Balfour says regarding it: "in Mammalia the pos-
terior part of the primitive infundibulum becomes the
corpus albicans, which is double in man and the higher
apes."

Though it must at once be acknowledged that no living
animal presents transition conditions that fit in with all
the requirements of the case, the explanations above given
are so well correlated with the morphological requirements
that such suggestions are at least permissible, specially see-
ing that no equally helpful ones have been forthcoming.

The proboscis-sheath or rhynchocoel, as studied by
different observers, is a strong muscular tube, which in sim-
pler groups of nemerteans extends only one-third back-
ward from the head. But in most of the nemerteans it
stretches from behind the dorsal ganglion to the anal region
of the tail. Anteriorly it unites with the rim of the pro-
boscis by a circular zone named the rhynchodoeum by
Burger. It is at this zone that sudden rupture of the
sheath from the proboscis may occur, when an animal is
strongly irritated. A gradual but permanent separation of

76 Evolution and Distribution of Fishes

the two evidently took place embryologically, when the
sheath became — as suggested by Hubrecht and fully ac-
cepted by the author — by degrees modified into the noto-
chord. We have already pointed out that this circular
zone corresponds to the velar rim in vertebrates.

Structurally the proboscis-sheath consists of an external
circular and an internal longitudinal zone of thick mus-
cular fibres, which posteriorly tend to intermix. Filling
the cavity of it and surrounding the proboscis, is a corpus-
culated fluid, except in the marine metanemertean genus
Cerebratulus, where the corpuscles* or loose cells seem by
multiplication largely to fill up the posterior part of the
cavity with a loose nucleated cellular mass. So, as Hu-
brecht remarks, the cavity may become "sometimes even
entirely obliterated." He adds (^7:361-63): "we might
picture to ourselves the eventual conversion of a hollow
proboscidian sheath into a solid notochord, the more so
as functionally the proboscidian sheath in nemerteans may
already be looked upon as an axis, around which the other
organs symmetrically arrange themselves as they do around
the notochord in vertebrates. It must at the same time be
borne in mind that the muscular coating in this posterior
portion is found to be considerably reduced and replaced by
a more or less homogenous and comparatively thin sheath."
But the writer would emphasize that in the last detail the
resemblance becomes the more marked to the vertebrate
notochord.

Now, if in a remote geologic past, namely In Ordo-
vician or in lower Silurian time, organisms like metane-
merteans existed rather abundantly, a stage may well have
been reached when the proboscis-sheath became, from en-
vironal action and proenvironal response, more and more
a mechanical and strengthening cylinder, rather than as at
first a protective sheath for the highly sensitive proboscis.
The latter then might have its structure and function more
and more condensed into the head region, while the muscu-
lar substance of the sheath might by degrees become
changed Into "a more or less homogenous sheath of fibrous
tissue." As condensation and morphological conversion of
the proboscis took place, separation of the proboscis sheath

Evolution of Fishes from Invertebrates 77

anteriorly from it along the rim region (rhynchodoeum)
would be effected. Thus the way would be clear for the
ventral brain ganglia, and for the ventral commissure that
united these to rise closely upward and in front of the
blunt anterior end of the evolving notochord, till placing
of the ventral ganglia, somewhat behind, but close against
the dorsal ganglia would be effected.

The writer then, in view of this and the many other
details of structural similarity that he now shows to exist,
would emphatically advance on Hubrecht's decidedly cau-
tious position when he says: "I need hardly insist upon the
fact that I do not advocate any direct relation between
existing nemerteans and existing vertebrates; my argument
goes no further than the attempt to show that the general
plan of structure of a nemertean is more in accordance with
that of a vertebrate animal than is, for example, that of
the Archiannelida." So many exact structures correspond
in both groups, or are carried forward from a more prim-
itive nemertean to a more evolved chordate state, that
the writer would claim a continuous evolutionary sequence,
even though some desiderated and highly important inter-
mediate stages are still wanting.

IX, The Nervous System.

This eminently confirms the above conclusions. The
writer has already dealt at considerable length with it (/:-
433-441 ), but some details deserve emphasis here.

The brain in most metanemerteans consists of two rela-
tively large dorsal or anterior brain-lobes, that are united
by a dorsal commissure. The latter, from its apparent
homology with vertebrate details, we can call the anterior
commissure. In nemerteans and in fishes the writer has
pointed out that a median nerve starts from the middle
of the anterior commissure. In nemerteans and in the
simpler turbellarians, zoologists have for years called this
the dorsal nerve. But in fishes and higher vertebrates it
has been called from its discoverer Reissner's fibre. It
is again referred to below.

While the anterior or dorsal brain-lobes remain simple
in most of the metanemerteans, in the genus Eupolia at

78 Evolution and Distribution of Fishes

least these are deeply divided crosswise into an upper an-
terior and a lower posterior pair. Such a condition may well
have been common to many extinct nemerteans, and it sug-
gests the probable primitive origin of the ancestral fore and
mid brain of vertebrates. The ventral brain-lobes that,
on separation of the sheath-notochord from the proboscis-
pituitary body, seem to have risen upward so as to be
behind the dorsal masses, could then become the hind
brain, while the strong commissure joining them suggests
origin of the pons varolii of the vertebrate brain.

The above then suggests that the brain masses in higher
nemerteans consist of an anterior and superior pair of lobes,
and of a posterior and inferior pair of lobes, all united
by commissures. Further, the superior pair may — as in
Eupolia — undergo subdivision into what would then become
an anterior and a median pair. Now in relation to the
evolving vertebrate brain Graham Kerr {43) has made
some highly important observations. For on the basis of his
study of the dipnoan brain he concludes that the vertebrate
brain primitively consists of two brain masses, an anterior
and a posterior. And in relation to the paired lobes of
nemerteans his study of the three genera of living Dipnoi
causes him to conclude "that the hemisphere region is
primitively paired," and so is "against the more generally
accepted view that the hemispheres are to be looked on
as the terminal region of the brain, as a 'telencephalon' in
the sense of His." The above views he has further
elaborated in his recent volume on "Vertebrata" (^^:85).

The brain substance of metanemerteans and of fishes
consists of zones of gray and of white matter, the gray sub-
stance being specially rich in large ganglionic cells.

The primitive beginnings of the spinal cord in fishes
have been variously outlined and interpreted by different
workers. Hubrecht first clearly set forth a possible ex-
planation, and connection evolutionarily, with nemerteans.
In the latter two main cords run continuously backward
from the ventral brain-lobes as the lateral nerves. These
may vary in position from lateral to slightly latero-ventral
or latero-dorsal. In the marine genus Langia however they
are markedly dorso-lateral. But in metanemerteans toward

Evolution of Fishes from Invertebrates 79

the posterior end of the body, the two nerves gradually rise
upward and form a posterior commissure above the intes-
tine. Now were such a close connection to be gradually
carried forward toward the brain region, the result would
be that an apposition and ultimate more or less complete
dorsal fusion would be effected between the two lateral
nerves.

But in rhabdocoel turbellarians and in metanemerteans
two dorsal nerve threads gradually come together and fuse
lengthwise as the median dorsal nerve of the latter group.
This nerve, according to most authors, springs from the
dorsal brain commissure, and there arises by two distinct
roots. Now in the vertebrate brain a fine nerve arises in
median line from the anterior commissure but by two roots.
This, first observed about sixty years ago by Reissner, has
been traced to occur in the entire vertebrate series by a
number of workers. Its main investigator Sargent {^3:
129) states that it tends to suffer degeneration only in
animals like the blind cave fishes, where the eyes have more
or less become functionless or absorbed. In its backward
passage from the brain this nerve fibre becomes embedded
between the substance of the lateral thickenings of the spinal
cord, and tapers out near the anus.*

Further, in rhabdocoels and in worms as a great group,
two ventral nerve threads start from the ventral gan-
glia of the head and run backward, either widely apart, or
somewhat near each other, or closely apposed. These, in
the more evolved "worms" and in "arthropods," become
the dominant nerve tracts, while the lateral and the dorsal
pairs of nerves become feeble or are absorbed. In meta-
nemerteans these ventral threads are moderately represent-
ed as median nerves of the lower surface. So in these latter
account has to be taken of three pairs of longitudinal nerves,
as a whole: (i) the ventral median nerves that are only
moderately developed but have become the main ones in
worms and in arthropods; (2) the lateral or latero-dorsal
nerves that are the specially strong ones in metanemer-

*The writer is unable to accept the views of Nicholls on this subject (46: 1). His
conclusion that the median dorsal thread is a muscle, is entirely uncorrelated with any
like structure in other animals. His paper throughout is characterized by a malignant
and unscientific spirit that is wholly regrettable.

So Evolution and Distribution of Fishes

teans, and that run backward on each side of the body to
form a union above the intestine; (3) the two dorsal
nerve threads which — more or less separate and important
in rhabdocoels — have fused lengthwise except at their roots
and are only moderately strong.

In transition to the vertebrates the following seems
to have taken place: (a) the strong lateral nerves, that
in metanemerteans have already formed a commissure
above the intestine, have gradually risen upward dorsally,
from behind forward, till apposition and lateral union of
the two nerves have been effected forward to their root
origin from the ganglia; (b) during this process the dor-
sal paired nerve has by degrees become surrounded by
the uprising lateral nerves, and its important optico-motor
functions have by degrees been usurped by the laterals,
so that it suffers marked reduction and degeneration; (c)
the ventral pair of nerves or "mundschlund" system of
Burger "from its origin along the lower posterior edges
of the ventral brain-masses, and its abundant distribution
round the mouth, the pharynx, the alimentary canal, and
the skin, would correspond with the ventral nerve threads of
Turbellarians. This seems gradually to have evolved into
what might be termed the ventro-sympathetic in proto-
chordates, and later into the sympathetic system of cyclo-
stomes and higher vertebrates." (7:440).

As indicative of such gradual evolutionary changes it
is noteworthy that in Amphioxiis {Branchiostoma) and in
true fishes, the first rudiment embryologically of the spinal
cord appears as an epiblastic groove, that spreads forward
from the anal region, and on either side of which arises
a plate or thickening of tissue lengthwise that we would
interpret as the lateral nerves of metanemerteans. By
gradual uprising, thickening, and fusing of the upper edges
of these plates the neural canal is formed. As the two
lateral plates or nerves continue to thicken they so press
on the canal as to convert this into a median slit. But in
Amphioxiis the complete dorsal fusion of the plates or
nerves anteriorly is not effected, so that a dorsal "longi-
tudinal cleft" is left. It should further be noted that in
metanemerteans a copious anastomosis of nerve-fibres takes

Evolution of Fishes from Invertebrates 8i

place between the lateral nerves, and so such fibres establish
a commencing condensation and correlation-relation between
these lateral nerves, that must aid in their subsequent
approximation and union. This correlation and anastom-
osis is further advanced in chordate animals.

X. Structure of the sense-organs.

The external aspect and relation of the sense-organs
have already been dealt with. As to their minute structure
and mode of origin, highly interesting and connecting stages
of evolving complexity can be traced, some points of which
have been dealt with above, (a) The nasal organ as ac-
cepted by the writer for nemerteans, is supplied abundantly
by nerves which pass off from the anterior region of the
dorsal brain-lobes. "As described and figured by Burger
the epithelial cells of each nasal depression consist of cil-
iated sensory or olfactory cells, that alternate with inter-
stitial or supporting cells, an arrangement exactly similar
to that seen in the vertebrate olfactory organ."

(b) The eyes in higher nemerteans show a minute struc-
ture and sensory complexity that closely allies them in
ascending series with the eyes of vertebrates. Nerves pass
to them from a lateral part of the dorsal brain-lobes, that
seem exactly to correspond to the optic brain centres in
the mid-brain of fishes. Each eye shows a cup-shaped
depression composed of columnar retinal cells, a pigment
zone, a finely granular cup-substance, an optic capsule, and
delicate ganglion cells that pass to and end below the
columnar cells. In the young of Petromyzon and in Myxine
the eyes are now reduced to two functional on either side
of the head, and in the former to two vestigial eyes that are
in sub-median or median dorsal position on the head, these
being the pineal and parapineal or parietal eyes of authors.
The functional ones then are scarcely more complex than
in higher nemerteans, being still devoid of lens, cornea, and
sclerotic constituents, as well as eye-muscles. But in the
adult Petromyzon these have all been formed, and are con-
tinued in higher fishes, where such additional complexities
as a choroid gland, a cartilaginous or osseous sclerotic lay-
er, a retinal tapetum lucidum, etc., arise

82 Evolution and Distribution of Fishes

As already noted, two of the typical four eyes present in
most species of Geonemertes and other related genera,
seem to have an exceptionally suggestive history, as tran-
sition is made from these to cyclostomes and higher verte-
brates, not least also, if accepted interpretations are cor-
rect, to some of the most ancient fishes. For from detailed
study of the past quarter century it is now generally ac-
cepted that the parietal eyes, or pineal and parapineal
organs, seen in lampreys and other vertebrates, represent
two more or less degenerate eyes. Studniclca's detailed
work on the European freshwater lamprey {47) and that
of Dendy on the New Zealand freshwater lamprey {48:
I ) as well as studies by the latter and by Cameron on
higher groups all fortify such a conclusion. In position
these arise behind the olfactory swelling, and in the lam-
prey a larger upper and a smaller lower one are in line
with each other. In the New Zealand lamprey — Geotria
— Dendy says "the larger and better developed of the two
does not lie above but behind the smaller and less well-
developed organ, so that both are distinctly visible when
the brain is viewed from above." He considers however
that they probably were paired organs primitively.

As in the eyes of the higher nemerteans and of larval
lampreys, the pineal organ is circular and shows a retina,
a pigment layer, a pellucida, a capsule, and a ganglionic
cell-system, the last being prolonged from near the pos-
terior commissure. Dendy considered that the pineal organ
at least can still function as a light-perceptor. It is of
interest also to observe that in some large though primitive
and long extinct fishes to be described later, a distinct
opening or openings occur in the cephalic buckler, that is
probably indicative of the presence in these of parietal eyes.

(c) The auditory organs. These have already been
generally referred to. Their internal structure has been
described by the writer (7:429-431) as follows:

"The 'cerebral organs' of nemerteans have been much
discussed, though unanimity of opinion as to their function
has not yet been reached. These however seem, like most
other parts of nemerteans, to be the simple rudiments
of more evolved structures in vertebrates. They are

Evolution of Fishes from Invertebrates 83

paired organs developed along the postero-lateral sides of
the head. Each in its simplest state is 'a mere groove in
the epidermis not extending deeper than the basement mem-
brane; it is lined by ciliated cells, and at the bottom are
large gland cells; while the organ is supplied by nerves
from the dorsal ganglion of the brain. In Carinella rubi-
cunda and others the groove becomes an oblique canal, the
blind end of which is surrounded by a mass of ganglion
cells, lying outside the cutis. In the higher forms the
canal penetrates deeper into the body as far as the brain.
The gland cells and the associated nerve tissue increase in
amount, and the canal becomes differentiated into two
regions — an extra-ganglionic 'lateral canal' and an intra-
ganglionic 'cerebral canal' (c) which frequently termi-
nates in an enlarged sac. In Drepanophorus the cerebral
canal is quite exceptional, in that it bifurcates, one branch
terminating in a sac with sensory epithelium, the other
being glandular; this in D. crassus extends backwards be-
yond the brain as a free tube. In several genera of this
order the cerebral organ lies in front of the brain {Tetra-
stemma, sp. of Eiineviertes, and of J m phi poms) ; in others
it lies at the side, and in still others behind the brain —
in which case it attains a great size. In all cases the organ
is separate from the dorsal brain mass, from which it re-
ceives nerves.' (Benham in Lank. Zool. IV, p. 185).

"A comparison with the embryology and structure of
the vertebrate ear leads us to believe that here one has to
deal with evolving stages leading toward that organ. The
accompanying diagram, copied from Burger's beautiful
work, is suggestive, and can be compared with a figure
of the embryonic ear in a mammal.

"It is now well recognized that the ear is innervated
by two distinct branches of the auditory nerve, and that
it performs a double function. The cochlear branchy dis-
tributed to the cochlea and ampullae of the ear, enables
the latter to perceive sounds; the vestibular branch that
passes to the semicircular canals has for function the main-
taining of equilibrium, or, as we would suggest is geoper-
ceptive or geotactic.

84 Evolution and Distribution of Fishes

Fig. 6. — a (to left) cerebral organ of Drepanophorus compared as an
auditory organ with b (to right), the young auditory organ of mammal, o, 6
open or closed external orifice; du. coch. ductus cochlearis ; s. u. ca. sacculo-
utricular canal; utr. utriculus; sac. sacculus; d. n., v. n. dorsal and ventral
auditory nerves; du. endo. ductus endolymphaticus.

"In Cerebratulus, as described and figured by Burger,
the external orifice, the ciliated canal, the two diverticula,
and the distinct nerve branches seem well to correspond
to the ear orifice, the ciliated lymph duct, the sacculus and
utriculus, and the cochleo-vestibular nerves of the ear.
That of Drepanophorus is even more exact. Two to three
auditory nerves here are inserted between the two organs,
the sacculus and the utriculus, as in vertebrates (Fig. 6a),
the maculae extend along their base, while the elongated
process seems from position, relation, and shape to repre-
sent the ductus endolymphaticus.

"If the comparison made above be correct it follows
that the ductus cochlearis of vertebrates and not the ductus
endolymphaticus, represents the primitive invagination tube
of the auditory organ. Further, the elongated process
shown for Drepanophorus in Fig. 6a suggests exact homo-
logy with the ductus endolymphaticus of vertebrates;
while Biirger's statement, that it passes backward and be-
comes embedded in the cellular tissue of the body, recalls
the often extensive ramifications of it in many freshwater

Evolution of Fishes from Invertebrates 85

teleosts. The opening of its upper end on the dorsal surface
of the head in elasmobranchs would then represent a special
new formation. The histological description of the organ
given by Devoletzky suggests that ciliated sensory epithe-
lium and supporting cells are here often surrounded bv a
mass of nerves as in the vertebrate ear; while the secretion
of mucus from surrounding gland cells and the presence
often of refractive 'kornchen' — that are possible rudiments
of otoliths — is most instructive."

"A minute comparative study of living nemerteans may
yet reveal more exact relationship, while the group seems
to present us with suggestive stages from a comparatively
simple type like Carinella up to a high degree of organi-
zation. It will be noted, however, that the auditory func-
tion seems largely to predominate over the equilibrating
one, since no distinct semicircular canals are traceable.
But when we remember that only one exists in Myxine,
and that two are alone formed in Petromyzon, we need
not wonder if. the equilibrating function here is diffused
along the sides or bases of the sac attachments."

XI. The blood-vascular system.

Some authors have held that the primitive vascular sys-
tem in vertebrates consisted primarily of a dorsal and a ven-
tral vessel. Thus Bridge {36: ^^A-) says: "There is little
doubt that, primarily, the vascular system of vertebrate
animals consisted of a dorsal artery (dorsal aorta), running
along the median dorsal line of the alimentary canal, and a
ventral or subintestinal vein similarly related to the ven-
tral surface of the digestive tube. The two vessels were con-
nected by a series of pairs of lateral branches, which had
their origins from the dorsal vessel, and, by their subdivi-
sion, formed a capillary network in the walls of the aliment-
ary canal. From these networks paired veins issued and
opened into the subintestinal vein." We can now compare
the above with the system in meta- and hetero-nemerteans.
In these the main vascular system consists of a longitudinal
dorsal vessel that runs in line between the proboscis sheath
and the alimentary canal, also of two lateral paired trunks

86 Evolution and Distribution of Fishes

that nearly always keep a course in close proximity to the
lateral nerves, and so are widely apart from each other.

The position and course of the dorsal vessel exactly
agree with what we find in the dorsal aorta of vertebrates.
In both also numerous lateral metameric vessels are given
off to the body tissues, from near the head on to the tail
region. The lateral vessels are of more doubtful value,
but seem to have a direct homology with one of two ver-
tebrate systems, namely either the lateral veins or the
posterior cardinals. But since they are in line with two
cephalic veins, and fall into a common "venous sinus" cavity
with these, they probably together behave as anterior and
posterior cardinals. Now if the three main nerves — the
dorsal and the two laterals — stand in intimate relation to
these vessels for metabolic purposes, we might expect that
when the lateral nerves gradually rose upward to unite
dorsally, these cardinals would follow a similar course as
transition took place from nemerteans to primitive fishes.
Their position in vertebrates suggests that this is what
happened, while a transition condition of blood vessels and
nerves is seen in Langia, one of the marine heteronemer-
teans. Such a migration dorsad of the lateral veins, from
an originally lateral position, alongside the lateral nerves,
is strong proof that the two plates or lateral thickenings
of the spinal cord, represent the dorsal uprising and fusion
of two originally lateral nerves.

Again In several metanemerteans, and for Amphiporus
pulcher in particular (6:243) an anterior pair ot vessels
forms abundant anastomosing ramifications behind the
brain and cerebral organs, also in near position to where
an anterior as well as succeeding pairs of gill-clefts might
be formed In later evolution, for aeration of the blood.
These make up the parastomodeal network and the ves-
sels constituting it gradually reunite into what seems to be
the homologue of the vertebrate ventral aorta. This, as
in vertebrates, joins what may well be called the sinus
venosus.

As to the structure of the blood vessels Dendy has made
some valuable observations on the Australian land nemer-
tean already referred to. He shows microscopically that

Evolution of Fishes from Invertebrates 87

each vessel has an internal nucleated zone, which suggests
a bounding epithelial layer, but of this he is doubtful.
"Outside this nucleated layer there comes a thin layer of
very delicate fibres, doubtless muscular, arranged in a cir-
cular direction around the vessel. Outside the muscular
layer comes a single layer of large vesicular-looking irreg-
ularly ovoid cells, with small nuclei and slightly granular
contents. The wall of the vessel then, in its narrow por-
tions, is made up of three distinct layers." If the inner-
most layer should prove to be a continuous endothelium,
the structural agreement with average vertebrate blood-
vessels is perfect.

The writer has already (7:444) summed up the mor-
pho-physiological conditions, as to the methods and direc-
tion of blood-circulation thus:

"The distribution of the blood-vascular system in the
Nemertinea has been carefully studied during the past
sixty years, though we still desiderate fuller physiological
details. While the simplest system (e. g., Cephalothrix)
shows only two longitudinal vessels in close proximity to
the lateral nerves, in higher forms there are two lateral and
a dorsal vessel, which with accessory vessels to the pro-
boscis sheath, and transverse ones connecting all, show a
marked anticipation of the vertebrate vascular system.

"In considering this system further, alike in its own
distribution and in its aerating and excreting connections,
we believe it is correct to consider that proximity to the
nervous system for metabolic renewal of the nervous sub-
stance, and the periodic transfer of Its blood to some aer-
ating region or regions, are of prime importance. The
former is effected by the frequent formation of expansions
of the blood-vascular system into two longitudinal sinuses
near the brain, and the passage of blood-vessels parallel
to the nerve trunks. The latter is effected by those expan-
sions that run parallel to the proboscis sheath, or near to
the cephalic groove, whose vessels seem to correspond to
the posterior cardinals of Cyclostomata and higher forms,
since in all extensive connections are made by these vessels
with the renal or excretory, and with the reproductive
svstems. In the forward course of these vessels to the

88 Evolution and Distribution of Fishes

heart, In the nemerteans as in the cyclostomes, the posterior
cardinals run directly beneath the sheath or notochord.

"In many genera these two vessels unite anteriorly Into
a common cavity that seems to correspond to the venous
sinus In lower vertebrates, while two anterior veins that
often form a loop system In the front part of the head
and that also unite with the sinus, would equally correspond
to the anterior cardinals. A single vessel In the higher ne-
merteans, starting posteriorly from the anal commissure,
corresponds In origin, course, and position to the dorsal
aorta of most vertebrates, and It, along with the anterior
cardinals, gives rise to the above mentioned vascular loop-
system round the front part of the head, that agrees with
the circulus cephallcus of vertebrates.

"But further. In many Heteronemertlnea, an oral-
cervical pair of vessels (Schlundgef ass-system of Burger)
starts from a median ventral vein given off from the
cardiac ring or commissure, and which agrees In relation
with the ventral aorta of vertebrate types. These oral-
cervical vessels brainch repeatedly after the manner of
afferent branchial arteries, are In direct connection with the
— as we shall term them tentatively — anterior cardinals,
and ramifying round the cardiac organ and cephalic groove
agree well with the Internal jugulars. The anterior ending
of the median ventral vein, from which these spring, and
the side vessels given off from it In front of the mouth
(Burger, p. 254), agree well with the hyoldean sinus and
mandibular veins of lower vertebrates. The posterior,
fusion again of the oral-cervical vessels with the sinus
venosus-like enlargements of the lateral vessels constitutes
another agreement.

"Vessels which Biirger has called the proboscis-tube
vessels arise at their anterior end In vascular swellings, and
posteriorly join the lateral (cardinal?) veins. These
might therefore be the beginnings of the lateral veins of
cyclostomes.

"As regards the transverse vessels the description that
has been given by authors for the cyclostomes could accu-
rately apply for the nemertean segmental somatic arteries
that are regularly supplied to the myotomes from the dor-

Evolution of Fishes from Invertebrates 89

sal aorta. A corresponding series of somatic veins also
empty into the cardinals (laterals).

"As to the methods and direction of blood circulation
our knowledge is still vague. Burger considers that the
blood flows along the dorsal aorta which is the most power-
ful pulsating one. It then flows into the transverse vessels,
thence into the lateral vessels, from which it is propelled
forward. This, if fully proved to be correct, would agree
fairly well with the cyclostome circulation. Interesting
also is Bohmig's discovery in nemerteans of unicellular
valvular swellings that occur at irregular intervals along the
interior of the vessels, and there act as valves for the course
of the blood flow.

"The nucleated and often pigmented blood corpuscles
contain true haemoglobin in not a few cases, both of which
are characters that lead up to the vertebrates."

XII. The excretory or nephridial system.

In passing from the blood-vascular to the excretory
system, a highly important question presents itself. For
amongst the simpler types of invertebrate, no recognisable
blood-system is observable, though an excretory one exists
from infusors upward. The first beginnings then of the
former deserve to be traced. The writer, in regarding
the rhabdocoel turbellarians as ancestral to nemerteans,
suggested the following for them: "in view of the ex-
treme and varied ramifications of the excretory system in
'rhabdocoels' as described and figured by von Graff, in
view also of what is noted below regarding the joint blood-
vascular and excretory systems of nemerteans, it seems not
unfair to suggest that, in transition from the rhabdocoels
to the nemerteans, a portion and specially certain of the
main trunks of the excretory system in the former, may
gradually have been set aside for the double function of
tissue aeration and waste-removal, while the finer branches
and capillaries may have remained as excretory vessels
purely." He then went into details that favored such.

The writer was not then aware that Dendy and Spen-
cer had both suggested, some years before, a possible tran-
sition relation between excretory tubes and circulatory

90 Evolution and Distribution of Fishes

vessels (55: loi). It should also be observed that Hu-
brecht and Oudemans, almost simultaneously with each
other, (^9 :5i ;50 rsuppl.i ), showed that direct connection
may exist between the two systems.

Shortly stated then, the evolutionary history of the
excretory system, from nemerteans to higher fishes, might
be tentatively sketched as follows: In metanemerteans and
heteronemerteans a set of fine paired tubules became grad-
ually separated off from the main longitudinal vessels that
hitherto functioned in common with the tubules, as circu-
latory and excretory tubes. While the main vessels then
became more and more modified into a blood-vascular sys-
tem, formed migrant corpuscles, and inside these gradually
elaborated haemoglobin, the finer metamerically-arranged
tubes became purely excretory structures. These at first
seem to have been simple coiled tubules that closely sur-
rounded the blood vessels, in a few anterior ones, but later
in twenty to possibly forty or fifty longitudinal pairs. Each
tubule-coil opened externally by a minute lateral pore, as
still seen in species of the above groups; internally they
became increasingly elongated, closely coiled on themselves,
and by their blind ends maintained intimate contact with
the blood-vessels, by slightly enlarged swellings provided
with ciliate or "flame" cells. Such a system then, might
be called an archinephros. In transition to cyclostomes and
higher fishes the paired tubules of each side probably fused
during embryonic life-stages to form a longitudinal "arch-
inephric or segmental duct" that drew off the excretory
products and that opened up by paired pores into a urinary
sinus As a result, closure of the two rows of external pores
seems to have occurred, except for two posterior terminal
ones that we would correlate with the pair of abdominal
pores present in most fishes. In embryos of cyclostomes
the two ducts, along with twenty, condensing to six, and
even in adults to two, anterior pairs of coiled tubules can
be traced, and these together form the pronephros or
head kidney that is centred around the head-region. This
pronephros is more or less retained in some teleosts also.

A set of later-formed and more posterior tubules, that
similarly opened into the segmental ducts, and that may be

Evolution of Fishes from Invertebrates 91

from ten reducing to six pairs in number, formed the
mesonephros, that strongly suggests the middle set of ne-
mertean tubules. The two longitudinal ducts of these now
end behind in a common urinary sinus which opens into the
common cloacal area. But while the mesonephric tubules
were at first strictly symmetrical, "in myxinoids only do
they remain so. In other craniates, at all events through-
out the greater length of the mesonephros, a varying num-
ber of new tubules arise from masses of cells nipped off
from the first rudiment. All of the mesonephric tubules
are therefore derived from the same original series of
rudiments by a sort of budding. These secondary tubules
acquire the typical structure and relations," but since the
tubules then became crowded "their metameric order is
lost." (_5/:87).

Until more minute comparative study has been made it
would be impossible to say whether the most posterior
tubules of some metanemerteans are the forerunners of the
supposed metanephros of male elasmobranchs, and the
metanephros of higher vertebrates. Such seems a likely
explanation. The abdominal pores of most fishes would
appear, as noted above, to be surviving remnants of one
pair of tubule-pores seen in metanemerteans. Their paired
persistence in the most ancient classes (Dipnoi, Crossop-
terygii, Holostei, Chondrostei, and most Elasmobranchll),
their occasional persistence only in a few Teleostei (Mor-
myrldae, Salmonldae), and their disappearance In most
Teleostei and In some specialized Elasmobranchll, favor
such a conclusion.

The higher nemerteans are dioecious as a rule, though
a few species of Tetrastemma seem to be truly herma-
phrodite. The former condition Is practically constant for
vertebrates, but a tendency to primitive hermaphroditism
is shown by Myxine, where sperms may be produced In
a younger, and eggs In an older stage of the animal.

XIII. The reproductive organs.

In Nemerteans the reproductive sacs are arranged in
numerous metameric pairs along the sides of the animal, and
alternate with the often paired lobes of the digestive tract.

92 Evolution and Distribution of Fishes

Each sac, as described and figured by Dendy, is a swollen
expanse of mesoblastic tissue lined by epithelial cells, and
that opens by a duct externally along the dorso-lateral
aspect. In cyclostomes the paired relation has been lost,
though it is retained in other fishes. But the sacs are also
mesoblastic and similarly constructed. The discharge of
the sperms or eggs, however, is effected in one of three
different ways, that are doubtless graded derivations from
the primitive nemertean type. The simplest is shown by
cyclostome fishes, where, instead of the sacs opening indi-
vidually by external pores as in nemerteans, the ducts of
the former now open into the body-cavity, and from here
the products are set free through two (Petromyzon) or one
pore, that opens into a cloacal cavity, and thence to the
exterior. In other fishes more complicated conditions have
developed, that fall under one of two heads. Thus, in
elasmobranchs, holocephalans, and possibly also in Dipnoi,
a split-off branch of the segmental or archinephric duct be-
comes the MuUerian duct that opens into the body-cavity,
receives the reproductive products, and conveys these
through the cloaca to the exterior. The most complicated
advance on nemerteans is seen in teleosteans, where the
lining layer of tissue round the ovary or testes becomes elon-
gated into a tube that conveys the products into the body-
cavity, and from the latter they pass through genital pores
to the exterior. Minor modifications on both types may
again take place.

XIV. Development of the egg.

Two types of embryonic development are known in
nemerteans, called respectively the direct and the indirect.
The former is typical of freshwater or land forms amongst
invertebrates, the latter develops amongst marine types.
The former occurs amongst protonemerteans, some meso-
nemerteans, and in all metanemerteans hitherto studied.
The latter is shown by some mesonemerteans and all he-
teronemerteans. Our knowledge regarding both modes
is still very fragmentary, but as holding the key to the
primitive development of vertebrates, should be most exact
and copious. It may be hoped then that fullest details

Evolution of Fishes from Invertebrates 93

will soon be forthcoming. We will here trace mainly the
"direct" mode, as being typical of all freshwater, land,
and some marine forms.

The egg undergoes holoblastic and nearly equal seg-
mentation inside the egg-case. The cells, pushing apart,
leave a large blastocoel cavity and soon all of these cells
form cilia. Next by invagination of half of these cells, a
two-layered gastrula is formed. In Amphioxus the egg
also shows holoblastic and nearly equal segmentation in-
side the egg-case, a similar blastocoel cavity is formed, and
invagination occurs. Only the outer or epiblast cells here
however become ciliate, though areas or patches of internal
ciliate cells may later be formed by the embryo. Amongst
cyclostome fishes Petromyzon shows holoblastic though
decidedly unequal segmentation; and this leads up to the
condition in Myxine which in this, as in so many other
modified and derivative details, shows a meroblastic type.
In the former a restricted kind of invagination takes place,
giving rise to a small-celled epiblast and a larger-celled
hypoblast, as is true also of Amphioxus. Cilia, however,
are absent and only later form on restricted areas of epi-
blast or hypoblast. In higher fishes either holoblastic or
meroblastic segmentation is seen, according to the group
studied, and variations also are seen in formation of epi-
and hypo-blast.

The embryo, when freed from the egg-case in all of
the above, soon assumes a somewhat elongate shape, and
in succession the neural ridges that unite to form the
neural canal, also the various anterior sense organs, appear
in all in fundamentally similar and successive manner.
Meanwhile a few cells, set free into the area between epi-
and hypo-blast, give rise to five patches or plates of cells
in nemerteans and in Amphioxus ; or two rather irregular
plates in Petromyzon and other fishes, which apparently
represent a condensation and fusion into pairs between
four of the above five. These are the first mesoblastic
rudiments of the coelomic plates. Alike in nemerteans and
in Amphioxus one plate is anterior, two are antero-lateral
and two are medio-posterior. In nemerteans by hollowing
out and continued growth of the posterior pair, the alimen-

94 Evolution and Distribution of Fishes

tary canal becomes surrounded by and hung in mesoblastic
folds, while the muscles and other mesoblastic tissues
originate from the anterior three. So Burger says: "in
einem Embryo, der einige Tage alt ist, verwachsen endlich
der nunmehr unpaare ventrale und dorsale Mesodermsack,
so dass nunmehr . . . zwei Zell-blatter existiren, von denen
das eine den Darm umgiebt, das andere der Korperwand
angepresst ist. Der Spalt zwischen ihnen ist grossen-
theils aus Mangel an Raum unterdriickt, kommt indess im
hinteren Drittel des Embryos in Gestalt einer ziemlich
geraumigen Hohle zur Ausbildung. JVir haben in den beiden
Zellbldttern Splanchnopleiira und Somatopleura, in der
Hohle ein Coelom vor tins."

The five plates in Amphioxiis behave much as in
nemerteans, but their gradual growth and changes have
been more carefully studied by several observers, to whose
results the reader is referred.

Reviewing all of the above comparative details, the
writer would strongly emphasize that the metanemerteans
show so many structural, functional, and embryological
characters which are either common from them to Amphi-
oxus and to Petromyzon or even to the higher fishes, or
they present so many characters which gradually lead up
from them to the three groups named, that they stand out
preeminently alongside all other invertebrates as the fore-
runners and phylogenetic ancestors of Amphioxiis, the
cyclostomes, and the true fishes.

But now it must be at once and freely acknowledged
that remains of nemerteans and even of cyclostomes are
unknown palaeontologically. The only doubtful represen-
tatives are the "conodonts" of Silurian and other rocks,
which are discussed in another chapter (pp. 107-09). But
this fact need in no way excite surprise, nor should it cause
one to reject the view that both groups may have existed
abundantly in Silurian, in Ordovician, or even — for nemer-
teans at least — in Cambrian times. For we should scarcely
have known of the abundant existence of many elasmo-
branch genera from the Devonian period onward till now,
had they not evolved the teeth, scales, and plates that occur
in Isolated fragments and abundant quantity in not a few

Evolution of Fishes from Invertebrates 95

rocks. But it can be asserted with entire confidence that
the primitive Silurian fishes undoubtedly sprang from some
ancestral invertebrate types of more archaic build. And the
metanemerteans are the only organisms which, not merely
in superficial aspect, but in minute structural detail, fulfill
the requirements of the case. Vigorous and continued in-
vestigation therefore of all available material, at all stages
in their life-history, will yield results of highest evolutionary
importance.

96 Evolution and Distribution of Fishes

CHAPTER IV.

The Physical and Biological Environment of Fishes.
(a) During the Silurian and Devonian Epochs.

It may be accepted as an almost invariable principle
that a study of the environal relations of any group of
organisms will prove a highly helpful guide in determining
the exact lines of evolutionary progression pursued by
such organisms. We desire now to apply such a principle
to fishes. If, as already emphasized in the previous chap-
ter, they developed from freshwater Nemerteans, we might
expect to find that so soon as any method of fossilization,
or any organismal parts capable of being fossilized, had
developed, traces might be got of the organisms of the
period in question. If, moreover, several distinct groups
of plants and of animals are found to be preserved side
by side in the same strata, such would pretty surely indicate
that these were more or less closely associated during life,
if not in the same environal medium, at least in one re-
moved at no great distance.

A study of the mass of stratified rocks that makes up
the Laurentian and Huronian systems of America has failed
to reveal recognizable organic remains, except possibly in
the upper strata of the Huronian. We are compelled to
accept it, however, that a varied invertebrate fauna had
already appeared, though most or all of the existing organi-
isms must have been soft-bodied. But when the Cambrian
rocks are reached an abundant marine invertebrate fauna is
encountered, the literature on which is synopsized in the
textbooks of Chamberlin-Salisbury (5:276-303), of Prest-
wich, of Geikie (7: II: 933-941) and others. Thus grapto-
lites, corals, trilobites, brachiopods, cephalopods and other
molluscs are often abundant. These form a biological
congeries that at once stamps the rocks in which they
occur as of marine origin. So far as yet revealed no
traces of lacustrine, fluviatile or land organisms have been
noted But land undoubtedly existed; for cliffs of erosion,
strata composed of fine shales or limestones, of coarser
mudstone or sandstone, and even rough conglomerates, are
all encountered often in continuous series. The writer has

In Silurian and Devonian Epochs 97

already advanced weighty evidence for the view that all
the marine organisms were secondarily derived from fresh-
water types that had previously evolved and lived amid
freshwaters. These, he claims, sent derivative offshoots
into littoral marine regions, which there fed and multiplied
abundantly. Partial proof of this is that nearly all of
the main invertebrate groups retain their most primitive
types in freshwater environment up to the present day,
(7:378-410).

But as we pass through the series of Silurian rocks a
striking change can be traced. By the earlier students of
these rocks their uniformly marine deposition was accepted
without question. And so far as the Lower Silurian or the
Llandovery and Wenlock beds of the Upper Silurian reveal
their secrets, their fauna is probably wholly marine. The
succeeding or Ludlow Rocks, however, indicate a marked
change over wide areas, alike of Northern Europe and
North America, and such can now be treated under the
succeeding caption.

A. The physical and biological environment of Silurian
Fishes.

We may begin with the now well known central English
rocks that are classed collectively as the Ludlow group,
since increasing study has been given to them and their
enclosed organisms in that region from about i860 onward.
First described by Murchison in 1826 {28: 12), and more
fully in "Siluria." {26: 137) two decades later, they were
examined in detail by Symonds (52: 193), then by Symonds
and Lambert (55:152) who described the exact succes-
sion and thickness of the beds, as determined during con-
struction of the Malvern and Ledbury Tunnels. This
succession beginning from below, deserves quotation —

"1, Aymestry rock with Pentamerus Knightii, etc. (lo ft.)

2. Upper Ludlow rock with Chonetes lata, etc. (140 ft.)

The Ludlow bone-bed seems to be wanting here.

3. Downton bed, thin (9 ft.) with Lingula.

4-8. Red and mottled marls and thin sandstone (210 ft.) with Lin-
gula and Pteraspis.
9. Gray shale and thin grit (8 ft.) with Cephalaspis and Ptery-
gotus.
lo-ii. Purple shales and thin sandstones (34 ft.)-

12. Gray marl passing into red and grey marl and bluish gray
rock (20 ft.), with Auchenaspis, Plectrodus, Cephalaspis,
Onchus, Pterygotus ludensis, Lingula and a Lituite (?).

98 Evolution and Distribution of Fishes

These pass upwards conformably into a series of red
marls, with yellowish gray and pink sandstone, containing
Pteraspis and Cephalaspis, and undoubtedly forming the
base of the Cornstone series of the Old Red Sandstone.

J. W. Salter in commenting on the fossils (p. 162)
gives Pachytheca sphaerica as a probable plant found with
the animals. Now the presence of marine fossils in the
Aymestry and in Upper Ludlow groups, and even the
continued occurrence of species of Lingiila in at least some
strata of the Downton and other higher beds, would incline
anyone who had even a slight "marine" bias to view all
of the beds and their organisms as marine. And in the
subsequent papers of Roberts-Randall (5^:229) and
of Randall (55:494) this is more or less accepted though
with a query. For in the latter paper Randall favored the
idea of a gradual change from marine surroundings in
the lower rocks to freshwater conditions above. The care-
ful record from Linley Brook of rock successions, given in
the earlier of these two papers is subjoined, as being of
value from the palaeontological standpoint.

VERTICAL SECTION OF THE BEDS EXPOSED AT LINLEY BROOK.

(a) Northern drift with boulders Feet. Inches.

(b) Upper Coal Measures

(c) Red Clays, unfossiliferous 6 o

(d) Light colored grits with plant remains 20 o

(e) Hard micaceous grits, charged with fish-remains. 7 o

Upper Bone Bed.

(f) Flagstones with current markings i 9

(g) Micaceous sandy grits with Lingulae o 11

(h) Greenish irregularly laminated rock with con-
glomerate I o

(i) Hard calcareous grit with broken Lingulae 1 o

(k) Laminated micaceous and sandy shale 20 o

(I) Gray micaceous grit o 6

(m) Micaceous ferruginous clays 6 o

(n) Yellowish sandstones (Downton Series) with
Beyrichiae and Lingulae, also two or more
ferruginous bands with large quantities of
dermal studs of Tlielodus, fragments of

Lingulae etc 8 o

Lower or Ludlow Bone Bed.
(o) Hard calcareous shales with fish-remains, Lingu-

1 ae etc 6 o

(p) Flaggy bed of impure limestone with Serpulites. . 4 o

(q) Hard impure limestone (Aymestry Series)

82 2

In Silurian and Devonian Epochs 99

Now in all of the above descriptions the Lingulae are
said to be either broken or the shells are heaped together
with the fish and eurypterid remains. Such may quite well,
therefore, have been derived as washouts and redeposits
from older rocks, or may have been washed up during
high seas and mixed with the fishes in coastal lacustrine
marshes. Further light is shed on this later.

If comparison be made of the organisms mentioned in
the two tables of the papers referred to above it will be
observed that, except for Linqula, the enclosed organisms
of the lower or Aymestry series are marine and are quite
different from those above, also that in the latter or Ludlow
and Temeside beds there are grouped mainly eurypterid
and fish remains, while Salter adds that "the plant which
Dr. Hooker described (Q. J. Geol. Soc. 9 (1853) 12) and
for which he now proposes the characteristic name Pachy-
theca sphaerica is the common fossil in the sandstone, and
accompanied as at Ludlow by plant remains and fragments
of Pterygotus."

Before offering any interpretation we may take up the
views of more recent observers. A. S. Woodward,
(5(5:429) in a valuable review of the relation between
the Lower Old Red and Upper Silurian as illustrated in
the Ludlow region, strongly inclined to view the latter as
passage beds from Old Red lacustrine conditions above to
increasingly marine ones below. But he was at times
puzzled by the biological relationships. Thus, he says

(P-435):

"The passage beds in question vary in different places

in constitution and thickness, but they all show the mingling
of truly marine fossils such as Lingula with the fishes and
eurypterids, which must have been able to live either in
the open sea or in lakes." Now in most of the above de-
scriptions the Lingulae are said to be either broken or the
shells lie on the surfaces of the shales, or as layers of tritu-
rated remains. Thus in the paper of Roberts and Randall
(p. 231) they specially note: (a) the abundance of Lin-
gulae that occur in two relations; either as well-preserved
shells upon the surfaces of the shales, or as layers of tritu-
rated shells: (b) the importance of the fish-fauna of the

loo Evolution and Distribution of Fishes

upper bone bed. W. S. Symonds again {57: 186) writes:
"Near Kington the bone-bed of the Upper Ludlow rock is
there over-laid by brown-colored strata containing a typical
Upper Ludlow shell, Chonetes lata. These beds are again
overlaid by strata containing the remains of fishes, especial-
ly the Cyathaspis Banksii and portions of the crustacean
Pterygotus and also two species of Eurypteri." So we
would again reiterate that such remains of Lingula may
quite well have been derived as washouts and redeposits
from older rocks, or may have been washed up from a
marine habitat during high seas and mixed with remains
of the fishes in coastal lacustrine marshes. Further light
is shed on this later.

As to the areal extent of this Upper Silurian Fauna
Woodward says: — "Its beginning is curiously marked over
an area of at least a thousand square miles by the Ludlow
Bone Bed, which is a layer of small and even minute fish-
fragments mingled with comminuted remains of other
animals which have been washed together. Notwithstand-
ing its great extent, this bone bed is rarely more than three
or four inches in thickness." Comparison with similar
beds of other lands strongly suggests that it may have been
many thousands of square miles in extent, and this is in line
with Woodward's suggestion of a possible correlation of
these beds with similar ones in Scotland and in the Baltic
area, a subject that is treated below.

A paper on "The Highest Silurian Rocks of the Ludlow
District" {38: 195) by Misses Elles and Slater is specially
detailed and suggestive. They say: — "In the Ludlow-
Downton district there exists an interesting series of rocks,
limited by the Aymestry Limestone at their base and the
Old Red Sandstone at their summit, and it is with these
that the present paper deals. Lithologically they present
a varied series of sediments ranging from limestones on
the one hand, through calcareous flagstones and shales to
shallow-water sandstones on the other; and these litho-
logical changes are associated with certain changes in the
fauna.

"Palaeontologically, these rocks are characterized by the
presence of Eurypteridae, which, although rare in the lower

In Silurian and Devonian Epochs

lOI

beds, gradually Increase in importance until they attain their
maximum development in the beds immediately underlying
the Old Red Sandstone. The rich brachiopod-fauna charac-
teristic of the lower beds dwindles and almost dies out with
the approach of shallow water conditions, although the
molluscs are somewhat more persistent."

"The recurrence throughout of conditions tending to
the formation of "Bone Beds" is also worthy of note, such
conditions having prevailed at four distinct times at least
during the deposition of the rocks."

As it is of importance here to compare the different
classifications of strata, and the views held regarding the
relation of the enclosed organisms of these strata, we ap-
pend the tables of Elles and Slater.

PURPLE-RED SANDSTONES AND MARLS OF THE
OLD RED SANDSTONES.

III.

Temeside

Group.

II.

Upper Ludlow'
Group.

Temeside
or
Eurypterus
Shales.

E. Downton-Castle
or
Yellow
Sandstones.

D. Upper Whitcliffe
nr
Chonetes Flags.

/. Gray carbonaceous grit — Fragment-
Bed,
e. Olive shales with Eurypteridae.

d. Temeside Bone-Bed.

c. Olive shales with Eurypteridae.

b. Gray micaceous grit.

a. Variegated shales and marls,
L greenish sandstones at base.

e. Micaceous sandstones with fish-

band and a few Lingulae.
d' Carbonaceous sandstones.

c. Massive yellow sandstones, with

Lingiila minima.

b. Plat>chisma Bed, passing laterally

into a Bone-Bed — ( D o iu n to n
Bone-Bed) .

a. Unfossiliferous sandy shales.

c. Ludlo^v Bone-Bed.

b. Calcareous shales and flags with

Spirifera ele'vata.
a. Calcareous olive flags with Cho-
netes elevata.

C. Lower Whitcliffe { b. Concretion-Band.

or Rhynchonella■^ a. Calcareous blue flags with Rhyn-
Flags. I chonella nucula.

I.

Aymestry
Group.

B.

Mocktree or j
Dayia Shales. /

Shales and limestones full of Dayia
navicula.

^. Aymestry or Con- (Massive limestones with Conchidium
chidium Limestone. I knightii.

I02 Evolution and Distribution of Fishes

After describing the lower and evidently marine beds
up to "calcareous shales and flags with Spirifera elevata"
they make the following remarks (p. 203) : "They are
immediately succeeded by the famous Ludlow Bone Bed
which is too well known to require description. It is best
developed at the lower end of the section, on the south
side of the road, where it is 2 J/^ feet above road-level, and
reaches a maximum thickness of nearly six inches. It is,
however, very commonly separated into two thin bands of
'bony' material, divided by a few inches of soft mud-stone.
In addition to the numerous fish remains which the Bone
Bed contains, we have identified Chonetes str'wtella, Orhi-
culoidea riigata and Orthis sp.; a similar fauna, with Bey-
ricliia in addition, being found in the softer mudstone
separating the "bony layers." And as to the higher or
Temeside group they write (p. 203) : — "Tenieside group.
The succeeding sandstones (Ea) differ somewhat in lith-
ology from beds" below. So the writers remark ^^They seem
to usher in new conditions; for, above the Ludlow bone-
beds, the articulate brachiopoda, so characteristic of the
lower beds, have almost disappeared, Lingulae and the
molluscan fauna alone remaining; and we therefore con-
sider that the dividing line between the Upper Ludlow and
Temeside Groups is best drawn at this horizon." Next
(p. 205) : "The overlying grit-bed which is conspicuously
'bony' at its lower and upper limits, is here seen at its
maximum development (2 feet), but, like the other Bone-
Beds of this Series, it thins away rapidly to west and east."
The bone bed (Fd) "which we designate the Temeside
Bone Bed may be regarded as a grey micaceous grit, in
which large fragments of bone and fish spines are dis-
seminated. There is, in addition, a considerable amount
of carbonaceous matter, but whether of vegetable or animal
origin is not clear. As a whole, this Temeside Bone Bed
is coarser and more diffuse than the Ludlow Bone Bed, and
very different from the latter in general appearance."

The succeeding olive shales {F,e) are 2 to 4 feet thick.
"Eurypterid remains are abundant," but hard to identify.
"These are succeeded by another grey micaceous grit, i foot,
(F,f ) at the top of which occurs a well marked layer crowd-

In Silurian and Devonian Epochs 103

ed with carbonaceous fragments, but in which bones are
rare. Purple-red sandstones with shaly partings come on
immediately above this 'Fragment-bed;' these differ in gen-
eral lithology from anything that we have seen at a lower
horizon; and since the 'Fragment-bed' at their base appears
fairly constant over wide areas and is easily recognizable,
we suggest its adoption as the upper limit of the Silurian
system in this district."

To complete the evidence required, their tables giving
the palaeontological distribution of all known species are
appended to the paper.

Now an inspection of this extensive table (pp. 219-20)
brings out very clearly that exactly the difference in fauna
of the freshwater Old Red rocks and the marine Devonian
rocks, observed in the next formation to be studied, applies
also here. For on p. 219 and the upper half of p. 220, the
organisms are all typical marine invertebrates which occur
below the Ludlow Bone-bed, if we except rare occurrences
of some brachiopod shells, which evidently represent a
temporary sea invasion or inwash, when the "soft-mud-
stone" was deposited (p. 203) between the Lower and
Upper of the two Ludlow beds. The organisms listed how-
ever on the lower half of p. 220 under "Crustacea" and
"Pisces" are freshwater, and attain their climax of abund-
ance alike in species and individuals in the Upper or Teme-
side Bone-bed and associated Olive shale. Here Pachytheca,
Eurypterids, Leperditia, Physocaris^ and abundant fishes
form a characteristic freshwater companionship, such as is
carried forward in facies into the Old Red rocks. The
intrusion here of a few Lingula shells can be quite readily
explained in one of at least four ways. But at present we
reserve discussion of this.

Observations made by King and Lewis (59:437) in
the South Staffordshire region closely parallel those just
given

On the east side of Scotland in the Pentland Hill region,
and on the west in the Leshmahagow region, members of
the Geological Survey have mapped Silurian areas that seem
exactly to correspond with the beds already described, and

104 Evolution and Distribution of Fishes

so these have been named by them "Ludlow" and "Down-
tonian" beds or by Goodchild (^0:599) the Lanarkian.

In addition to a varied assemblage of eurypterid and
fish forms, phyllopods belonging to the genus Ceratiocaris
are abundant, and as decidedly indicating nearby land life
a fossil scorpion, Palaeophoniis, and carbonized remains of
what seem to be lycopodineous plants are met with. It
is from the strata of these areas also that Traquair secured
the rich material on which his fish genera Lanarkia, Atele-
aspis etc. are founded.

In more recent years Campbell has published an im-
portant paper (7^^:923) on an extensive series of Down-
tonian rocks in South-eastern Kincardineshire, Scotland.
These he catalogues as follows :

Feet

7. Tuffs and tuffaceous sandstones 800

6. Grey sandstone and fossiliferous sand\' shales and mud-
stones ( with fish band ) 600

5. Red sandstones 60

4. Volcanic conglomerates and tuffs 40

3. Grey and brown sandstones with thin red mudstones. . . . 1000

2. Purple sandstones 60

1. Basement breccias with intercalated sandy mudstones.... 200

Regarding the above he states that No. 6 "alike in its
lithological characters and in its fossil contents, shows the
Silurian rather than the Old Red Sandstone affinity of its
succession." In these beds he "found not only Dictyocans,
but also Eurypterus sp. and fragmentary plant remains."
Of fish remains found by him there Traquair identified
( I ) Cephalaspidlan scutes belonging to a species as yet
unnamed and undescribed; (2) fragments of the median
plates of a beautiful new Cyathaspis named by Traquair
C. CampbelU. He has also found with these Ceratiocaris,
Archidesmus sp., and a new genus of Myriapod, — a prob-
able larval form of insect, a new species of Eurypterus, and
fragments of a scorpion.

In reviewing all of these therefore he concludes
(p. 934) : "In Kincardineshire no evidence has been ob-
tained so far which would point to marine sedimentation.
No undoubtedly marine organism has been found, and the
association of the eurypterids with plant remains, scorpion
fragments, galley worms, and a larval form of insect, ap-

In Silurian and Devonian Epochs 105

pears to show that the green and grey mudstones were
laid down in close proximity to a land area, and at the
most can imply only estuarine conditions."

Campbell further draws attention to the striking simi-
larity of beds described by Kiaer {61) for the Christiania
region, since the contained organisms seem at least generi-
cally identical, and include several types of fish.

Kiaer entitles his paper "A new Downtonian Fauna in
the Sandstone Series of the Kristiania area." This series
is fully 500 meters thick, and consists of a lower part rich
in shales, and an upper part poor in shales. Fossils and
clear trail marks only occur in the lower part, while the
richest horizon is a "gray-green calcareous and argillac-
eous sandstone, which can be easily split into somewhat thin
and irregular slabs." He describes the subjoined group
of wholly freshwater organisms :

(i) Dictyocaris, very common.

(2) Ceratiocaris, not often in good specimens.

(3) Eurypterus norvegicns, very common.

(4) Eurypterus minutus, rare.

(5) Eurypterus sp. rare.

(6) Pterygotus sp. rare, in fragments-

(7) Aceraspis robustus, very common.

(8) Micraspis gracilis, not common.

(9) Pterolepis nitidus, very common.

(10) Pharyngolepis oblongus, not common.

(11) Rhyncholepis par'viilus, common.

The five last were all new anaspid or hyperplacodous
fishes (p. 257) that show near aflinity with Scottish and
later evolved Canadian types. He regards the entire series
"of Phyllocarids, Eurypterids, and Ostracoderm fishes" as
freshwater, but records a set of marine types in what he
calls an "uppermost marine Ludlow zone." An almost
identical association of organisms also was recorded by J.
V. Rohon {16) in rocks of the island of Oesel in the Baltic.

During the past 30 years an examination of the Upper
Silurian rocks of the Eastern States and Canada has re-
vealed a surprising similarity — almost close identity — with
those of the Old World. Thus the lower strata of the
former region that have been called the Niagara and
Guelph seem to represent the Aymestry and related marine
strata of England. The succeeding and higher beds again,

io6 Evolution and Distribution of Fishes

agree closely with the top beds of the Upper Ludlow and
with the Temeside groups of England. In 1884 Claypole
described the primitive fish Palaeaspis from Silurian rocks
of Pennsylvania {62: 1224) and a few years later Mat-
thew (<5j:49) described another primitive type — Diplaspis
acadica — from Lower New Brunswick in Canada. He
correlates the rocks as Niagaran, but they may correspond
more nearly with the upper Salina and Waterlime beds of
the United States. Associated with the fish — much as in
the European beds — Ceratiocaris piisUhis "occurs in myriads
in the black fissile shales" (p. 55), and also a crustacean
Biinodella hori'ida. Matthew emphasizes three distinct
and rather widely separate localities for these Silurian
rocks, all of which are devoid of marine organisms, but show
freshwater types similar to those of W. Russia, S. Norway
(Kiaer), and Scotland. These are the island of Anticosti
in the Gaspe or eastern Quebec area of Canada; Arisaig
in eastern Nova Scotia; and along Passamaquoddy Bay in
southern New Brunswick. Of these he says: "Thus in
three districts of Acadia, the lower measures of the Silu-
rian series are represented by bituminous shales and lime-
stones to the north, and dark carbonaceous shales to the
south, which presumably are contemporaneous." And in
accepting that these belong to the Clinton groups he adds
that the fish remains "occur in the mass of strata included
in the 670 feet mentioned in the section at p. 165 of the
Report of the Geological Survey of Canada for 1870-71."

In "The Ancestry of the Upper Devonian Placoderms
of Ohio" Claypole {64 : 349) traces the relation of fish life
downward from the Devonian to the Silurian beds, and
speaking of the Salina beds says: "In these were found
the shields of Palaeaspis in great numbers. They are con-
sequently of equal age, to say the least, with the Pteraspis
of the Ludlow, all of the yet known specimens of which
except one solitary shield of Cyathaspis {Scaphaspis)
ludensis have come from the upper division."

But a marked feature of the American area is the ex-
tensive deposits or infiltrations of salt that have given the
name Salina to the group. Such deposits, however, are
restricted to certain beds, and suggest that wide but still

In Silurian and Devonian Epochs 107

shallow expanses were invaded at periods by the sea. The
waters were then isolated and their salt precipitated.

Before reviewing the above evidence, it should be stat-
ed that supposed fish remains have been reported from the
base of the Upper, or even from beds of the lower Silurian,
but the records are so scant, or the material is so doubtful
that we prefer not to found any views upon such. There
is no reason, however, why such records need not be verified
and even greatly extended in the future, for the most prim-
itive fishes almost certainly existed when the oldest Silurian
rocks were deposited.

Mention should here be made of an extremely abundant
type of organic remain that is scattered over many layers
of strata from Lower Silurian up to at least Carboniferous
days. For the small or almost minute brown to nearly
black shining bodies that have been named "conodonts"
or cone teeth, have attracted the attention of observers in
Russia, Britain, and not least in N. America. These in
some cases are simple cone-like teeth, which, when attached
to the animal forming them, were probably composed in
part at least of carbonate of lime, but may also have been in
part horny. But most show a compound structure, and con-
sist then of a tooth-plate that bears from two to many teeth
of varying size, number, and disposition.

Newberry, Hinde, and others have well compared these
with the teeth and tooth-plates of living Cyclostome fishes,
which however are wholly or largely of a horny nature. The
writer also has suggested that they may all represent evolv-
ed and complex derivatives from the horny teeth formed in
the mid part of the proboscis in Metanemerteans. For if we
accept that freshwater Metanemerteans may have swarmed
in Cambrian lakes and swamps, these by progressive change
may have given rise to Cyclostomes, some of which retained
horny teeth as in existing types, while others may have ad-
vanced to a more complex calcareous type.

The writer has arranged in Fig. 7, a set of illustrations
from a to r, some of which are the horny teeth of existing
Cyclostome fishes, and others are conodonts copied from
the works of Newberry and Hinde. The close resemblance
in many cases is at least suggestive. The writer also has

io8 Evolution and Distribution of Fishes

Fig. 7. Conodonts and cyclostomatous teeth, a. b. external and internal
labial teeth, Petromyzon fluviaiile; c, d, e, conodonts (from Newberry and
Hinde) ; /, maxillary tooth-plate, Geotria australis; h, do. G. chilensis; g,
tooth-plate of Conodont (from Newberry) ; i, mandibular tooth-plate, G.
chilensis; k, I, conodont tooth-plates (from Newberry and Hinde) ; m, tooth-
plate, Petromyzon marinus ; n, 0, conodont tooth-plates (from Newberry and
Hinde) ; p, lateral tooth-plate, Myxine gliitinosa; r, do. of conodont. Poly-
gnathus (from Hinde). All enlarged.

In Silurian and Devonian Epochs 109

pointed out, in the above quoted work, the curious facts
that living Cyclostomes are rich in oil, and also that sup-
plies of petroleum or rock oil, as well as abundant remains
of conodonts, first appear synchronously in Cambrian and
Silurian rocks. It may be hoped that added evidence will
soon be obtained as to the possible affinity or not of the two
kinds of structure.

In trying to condense and interpret the knowledge now
presented the writer would infer that most, if not all, of
the Lower Silurian rocks and even of the Llandovery-
Wenlock in England, or the Niagaran-lower Salina in
America, were deposited as marine accumulations, and so
include typical assemblages of littoral marine fossils, such
as are catalogued by many palaeontologists. But no un-
doubted fish remains occur with these. Such deposits were
adjacent to extensive though low-lying land-masses, which,
in the Upper Silurian period, were often extensively flooded
by invasions of the sea, so that the freshwater and the
marine life at times became mixed. The types at that time
ablest to survive such oscillatory changes, were mainly
species of Lingula or Chonetes, which may be found along
with a varied littoral marine life, or at times occurring in
depauperate state, or in the Upper or freshwater beds their
remains occur as washed out and redeposited shells, along
with what evidently was a widespread freshwater fauna.

Such oscillatory changes were due to widespread vol-
canic action, as recorded by various geologists, and as sum-
med up for East Scotland by Campbell as follows (op. cit.
935) • "One must conclude that early in Downtonian times
(or perhaps in pre-Downtonian but subsequent to the move-
ments which folded the eastern schists) volcanic activity
had already begun in the schist country to the north of the
Highland Fault."

But In pre-Downtonian and Mid-Salina times the sea
gradually retreated and left extensive N. European — and
evidently N. E. American — continental areas of no great
elevation, that were traversed by far-reaching river systems.
These rivers must have often expanded into marshes or
shallow lakes, that in their periodic change of level during
dry and wet seasons, simulated the drainage areas of the

no Evolution and Distribution of Fishes

Amazon, the Congo, or the Nile. Abundant deposits were
thus made annually in some places, continuously in others
where they would give rise to fine shales or lime precipitates,
to coarse cherts or sandstones where they were laid down
nearer the main river-beds, or to coarse conglomerates
where adjacent to the main river-channel. For the state-
ment made by Campbell (p. 935) when speaking of these
very rocks: "the coarse volcanic conglomerate, like those
of the Old Red Sandstone, is in all likelihood a torrential
flood gravel" is exactly duplicated by Baldwin Spencer, in
his description of the "Neoceratodus" region of Australia,
that is cited on p. 32 of this work.

The bone-beds, varying in number from one to as many
as five in some areas, that so sharply appear amongst the
other strata, and which may be from a half-inch to as much
as nine inches in thickness, can be exactly explained as
sudden deposits of volcanic dust that, in a few hours or
days, had entombed and preserved myriads of plant and
animal remains.

The biological assemblage of these Upper Silurian
deposits can now be considered. Except for the presence
of some species of Lingula in intercalated beds, or the oc-
casional intrusion of stunted forms amongst others to be
now named, the entire group of organisms is totally differ-
ent from that found in the typical marine strata of the
lower Silurian, the Ordovician, or the Cambrian. Myriads
of the phyllopod genus Ceratiocaris ; such genera of the
Eurypteridae as Pterygotiis and Eurypterus; entire ex-
amples or more or less broken fragments of the scorpioid
Palaeophonus ; a new genus of myriapod; tubercles plates
or entire examples of primitive fishes belonging to such
genera as Thelodiis, Lanarkia, Lasaniiis, Cyathaspis, Ceph-
alaspis, Auchenaspis and Tremataspis; abundant remains of
the problematic plant Parka decipiens; and not unfrequent
lycopodineous specimens; make up the whole.

Now the writer hopes to show elsewhere that species of
Ceratiocaris like many other of the simpler Crustacea, are
and have been freshwater in habitat. The history of the
Eurypteridae evidently is that from some primitive pre-
cambrian freshwater ancestor of the Arachnida, one line

In Silurian and Devonian Epochs hi

advanced to ultimate gigantic size and amid freshwater
environment, as the true Eurypterida. Another early
evolved amid increasingly estuarine and later littoral sur-
roundings as the Trilobita, while a third passed on to land
and gave origin amongst others to the Scorpionida. Now
largely on account of the intermixture or abundance in
intercalated strata of the entire or broken shells of de-
pauperate examples of Lingula^ more rarely of Chonetes,
Clarke and Ruedemann in their elaborate memoir {6^)
on the Eurypterida have concluded that these began as
marine organisms, and in late Silurian or Devonian time
became freshwater. The suggested evidence for a marine
life at any period is so scant or wholly wanting, and the
many facts in favor of a freshwater origin are so impres-
sive, that we accept the latter as true, and trust later to
demonstrate this fully.

As regards the abundance in individuals of the genera
of fishes already cited, this must have been prodigious over
wide areas. For the widespread continuity and similarity
of the Silurian bone-beds of America, of Britain, of Russia,
and of Sweden indicate that innumerable myriads must have
died within a few hours, and been sealed up entire and
preserved from subsequent destructive action; or after a
greater or less degree of disintegration, lasting possibly
over two or three weeks, the hard calcareous teeth or
plates or bones became piled together in layered masses.

The three groups of animals then, given in the above
study, whose remains are specially abundant are the cerati-
ocarid crustaceans, the eurypterids, and the fishes. The
possible origin of the oil or petroleum yielded by the Silu-
rian and later rock-strata has already been discussed. By
far the most likely source of such seems to be the animals
just named, and especially the fishes.

Finally as to the affinities of the Silurian fishes, all so
far as known belong to very primitive and now wholly ex-
tinct groups that are treated of later. The internal tissues
were undoubtedly soft and easily perishable; and even if
cartilage was present it also must have been of soft con-
sistence. So our knowledge of them is wholly confined to
the exo-skeleton, which in very primitive types like The-

112 Evolution and Distribution of Fishes

odus. or Lanarkia (Fig. 8a, 8b) consisted of scattered
tubercles embedded in a firm skin. More extensive deposi-
tion of calcium carbonate gave rise to such armored types
as Cyathaspis, Auchenaspis and Cephalaspis. Isolated
defensive spines, referred to the genera Onchus and Cli-
matius suggest that primitive forerunners of the Shark
alliance or Selachii were already evolving in Silurian fresh-
waters.

Owing to an environal combination of conditions that
is still often highly destructive to fish-life, but was then
undoubtedly greatly more active and widespread, such as
subaqueous earthquakes, explosions of poisonous gases,
widespread deposition of volcanic dust and ashes, severe
storms over land and lake areas, sudden torrential rise and
fall of the lakes, rivers, or swamps in which the fishes

Fig. 8, a

Fig. 8, b

Fig. 8. — a, Restoration of Thelodus scoticus, a primitive fish
probably derived from a metanemertean ancestry, b, Restoration of
Lanarkia spinosa. (After Traquair.)

In Silurian and Devonian Epochs 113

lived, rapid destructive transfer of sand, gravel, and even
small stones, all must have combined to produce a biolog-
ical wear and tear that would cause extensive migrations,
exposure to new environal surroundings and factors, rapid
specific variations, and evolution of increasingly divergent
types of organisms, often also sudden as well as widespread
death.

But in line with such results the question may well be
asked : Why did not rapid and wide migrations occur
from freshwater to littoral or suboceanic habitats? The
answer is evidently got when we remember that these
fishes were wholly or largely devoid of hard teeth, that they
were mainly of heavy flattened build, and were suited for
shuffling or grubbing after their food over muddy or sandy
surfaces. Above all, there is strong likelihood that the
seas and littoral regions were abundantly stocked with me-
dusoid and cephalopod organisms. For though we are
still unacquainted with the offensive or defensive parts of
these, it seems fairly probable that some of these were
formidable antagonists, which could drive back into fresh-
water such of the clumsy fishes as ventured into the sea.
So while related types to some of these primitive fishes
survived into the Lower and even into the Upper Devonian,
their place was gradually taken by more lithe, flexible and
resisting descendants.

We are therefore compelled to conclude that the most
primitive fishes known to us, originated wholly in fresh-
water areas, and are there known to us in countless myriads
as fossilized forms. The associated animals and plants con-
stitute with these a biological assemblage that are totally
different from marine organisms of the same period.

B. The Physical and biological environment of Devon-
ian fishes.

It is now generally conceded that at least throughout
Europe and North America a complete or almost complete
continuity in succession of the rocks can be traced from
Upper Silurian beds such as the Temeside, to others whose
organisms indicate transition to Devonian or Old Red
times. But the rocks of Central Russia show marked

114 Evolution and Distribution of Fishes

discontinuity, and so suggest volcanic action and displace-
ment. As for the Upper Silurian, so also for the Devonian,
we hope to show that two very distinct assemblages of
organisms characterize freshwater and marine deposits
respectively.

Over wide areas of the North Eastern United States,
of South England, of Northern France, Central Germany
and Russia, South-west China and New South Wales thick
deposits of marine strata, that enclose typical marine fos-
sils, have been followed out. To these the term Devonian
was restricted by some geologists. But distinct from such
beds, and often forming enormous stratified masses, occur
other deposits with a very different biological assemblage,
and which have had a very different physical history from
the former. To these the older geologists gave the name
Old Red Sandstone. In endeavoring to unravel gradually
the history of the relation and succession of these two
groups, the writer was at first completely bewildered, then
puzzled, still later in hopeful mood, and finally satisfied
as to exact explanations. Such mental phases were due
to the frequent description by the earlier geologists, of
blocks of fossils which had been collected in some one, or
in a few neighboring regions, but which had not been
exactly labeled as to stratigraphic occurrence and succession.
Or again geologists in the field had accumulated collections
which were described by colleagues, who had never or
seldom visited the rocks. Not unfrequently also one could
trace a distinct prepossession or mental bias, on the part
of some writer for an already-formed theory or opinion.

In study of these we may again start with European
strata, as they have been longer and more fully compared,
than those of North America or other continents. As now
synopsized by Geikie (7:982-999), by Prestwich (66:11:
74-82), by de Lapparent ((57:11:836), and by Roemer-
Frech (<5<^: 1 : 34-55 ; II : 117-256) the rocks of central Eu-
rope from south England eastward, and to which the term
Devonian was first applied by Murchison and Sedgwick,
are clearly marine, but largely littoral-marine in origin.
The nature of the rocks, the abundant lists of marine fos-

In Silurian and Devonian Epochs 115

sils, the absence of plants and animals that would suggest
freshwater conditions, all conspire to stamp them.

But probably contemporaneous with these, or at times
intercalated between them, as seems particularly to be true
of those in North America to be noted below, are extensive
and thick masses of rock, which from their predominantly
red color and high ferruginous content, were early named
"the Old Red Sandstone." These are largely confined — in
their known exposure — to Wales, to North and East Ire-
land, are very extensively developed in Scotland and Rus-
sia, and they appear also in Norway. Their great develop-
ment in North America will be referred to later. Studied
throughout Europe in succession by Murchison, Fleming,
Godwin-Austen, Ramsay, Hugh Miller, Mitchell, Agassiz,
Powrie, Geikie, Peach, Flett and many others, the strata
seemed to be divided into at least two or even three divi-
sions that were mainly characterized by their diverse fish
remains.

Geikie says regarding them (7:1007) : "The Old Red
Sandstone of Britain, according to the author's researches,
consists of two subdivisions, the lower of which passes
down conformably into the Upper Silurian deposits, the
upper shading off in the same manner into the base of
the Carboniferous system, while they are separated from
each other by an unconformability." This author made
a very detailed study of the entire system throughout the
British Isles, and alike in special papers ( (5^ : 3 1 2 ; 2j : 345 )
as well as in his exhaustive work "Ancient Volcanoes of
Great Britain" (70) has developed the view that the
rocks of both lower and upper divisions were enormous
lacustrine deposits, that occasionally reached a maximum
thickness of 30,000 feet. These were laid down in a
group of freshwaters which he named Lakes Caledonia,
Orcadie, Cheviot, and Lome, and of them he says: "There
is sufficient diversity of lithological and palaeontological
characters to show that these several areas were on the
whole distinct basins, separated from each other and from
the sea. The interval between the Lower and Upper Old
Red Sandstones was so protracted, and the geographical
changes accomplished during it were so extensive, that the

ii6 Evolution and Distribution of Fishes

basins in which the late parts of the system were deposited,
only partially correspond with those of the older lakes."

In a later study by Goodchild (77:591) he says: "as
regards its mode of origin there appears to be evidence of
a satisfactory nature that the whole of this vast formation
was accumulated under continental conditions, partly in
large inland lakes, partly as torrential deposits of various
kinds, partly as old desert sands, and partly as the results
of extensive volcanic action." He estimates the thickness
of the lower series as reaching in places to 20,000 feet,
while the upper, that he divides into an Orcadian, a Nairn,
and an Elgin set, may reach 17,000 feet.

As might be expected, the rocks that compose the Lower
Old Red Sandstone, while largely of a reddish ferruginous
tint, include red shales, grey and yellow sandstones, occas-
ionally — usually thin — limestone, or "cornstone" beds, and
in Forfarshire hard close-grained grey flagstones. Pow-
rie has described these in detail (72:413), and specially
refers to "one very extensive and highly fossiliferous Fish-
bed, holding an intermediate position among the flaggy
beds, continuous and apparently equally extensive with
them." He "found this fish-bed in Carterland Den in
Kincardineshire, near Farnell, at Turin Hill, in some quar-
ries south of Forfar, in many places on the Sidlaws, in Bal-
ruddery Den in Forfarshire, and in Rossie Den in Perth-
shire. It thus extends over a range of more than twenty
miles " As to its contents he says: "wherever this deposit
has been discovered it abounds in ichthyic and crustacean
remains, the former being far the more abundant."

Hull (7J: 225) has fairly well synopsized the condition
of affairs in the relation of the marine Devonian to the
freshwater Old Red Sandstone thus (p. 274) : "At the
close of the Upper Silurian period, represented in Ireland
by the Glengariff beds, in Wales by the Upper Ludlow
and Passage beds, and in Scotland by the Lower Old Red
Sandstone, there was a general elevation of all the northern
and western portions of the British Isles, accompanied by
flexuring of the strata, and followed by extensive denu-
dation. In the area of the south of England, however,
and adjoining continental districts it was otherwise. Here

In Silurian and Devonian Epochs 117

there was, on the contrary, continuous depression, and the
sea overspread this area, in which were deposited the Lower
and Middle Devonian beds. With the Upper Devonian
stages or Old Red Sandstone proper, the submersion of the
western and northern portions of the British Isles began.
Lacustrine conditions were established in the south of
Ireland, portions of Scotland, and the north of Ireland. In
the waters of these lakes the Old Red conglomerates and
succeeding beds with Anodonta were laid down."

Speaking of the Ludlow area (5<5:434) A. S. Wood-
ward says : "The red sandstones, marls, and included nod-
ular limestones (locally known as cornstones) ^ which are
definitely determined at many points to constitute the lower
part of the Old Red series formed in the "Welsh Lake,"
contain numerous fish-remains of the genera Pteraspis,
Cephalaspis, and Phlyctaenaspis. This is the typical Lower
Devonian Fish-Fauna, and occurs with slight variations
in regions as remote from each other as Cornwall, South-
ern Scotland (especially Forfarshire), Galicia, Spitzbergen,
New Brunswick and Newfoundland. The rocks containing
tlie fish remains, indeed, are almost identical in the Welsh
area, Spitzbergen, and Newfoundland; and if specimens
from these different localities were mixed it would be
difficult to separate them correctly. . . . Fragments of
Styloniirus and other Eurypterids are occasionally discov-
ered with the fish remains."

In contrast to the above observers Macnair and Reid
{74'- 106) have attempted a destructive criticism, and have
advocated a marine origin for the Old Red Sandstone beds,
but they entirely fail to show why a typical marine inver-
tebrate fauna is not associated with the enclosed organisms;
they fail to note the great abundance of Estheria mem-
branacea, which like the entire group of Phyllopoda — past
and present — have only freshwater associations; they do
not note that the plants found side by side with the euryp-
terids, fishes, and Estheria, are absent from the marine
strata. Other grave objections can be taken to their con-
clusions, even on lithological grounds. It should be said,
however, that occasional inroads of the sea, specially in

ii8 Evolution and Distribution of Fishes

the Welsh region, caused restricted deposits of typical ma-
rine fossils between the freshwater beds.

The biological assemblage of the European Lower Old
Red rocks in part slightly resembles that of the Upper
Silurian, but on the whole is markedly different. Mitchell
(75-145) '^^^ Powrie (7^:413) early noted abundant
though poorly preserved plant remains. Parka decipiens,
spores of Pachytheca, the myriapod Kampecaris forfar-
ensis, species of Eurypterus and Pterygotus anglicus as well
as a very rich fish fauna were recorded. More recent
workers have greatly extended their lists, and particularly
have encountered abundant remains of such land plants
as the fern Archaeopteris, also Psilophyton^ Sigillaria, and
Calamites.

Goodchild (77:591), Flett, and Campbell have given
detailed descriptions and lists from the north of Scotland,
while from the western part the Scottish Geological Survey
has contributed much.

So abundant and typical in some of these Caledonian
beds are definite organisms that Goodchild (p. 600) clas-
sifies some of them thus :

Myriapod Beds

Volcanic Rocks

Acanthodian Beds of Turin Hill

Cephalaspis Beds of Auchtertyre

Volcanic rocks

Pterygotus beds of Carmylie, etc.
All of these, from our present knowledge, are freshwater
beds.

The remarkable and unwieldy buckler-shaped Silurian
genera Cephalaspis (Fig. 9a) and Pteraspis are continued
into the lowermost or Caledonian rocks, that are exposed
in Forfarshire, in the Lome region, in Herefordshire, and
in East Wales (7<5:463), though the species as determined
by Traquair are different, Cephalaspis lyelli being the most
widely extended. The Acanthodians (Fig. 9e) or primitive
elasmobranchs of the Upper Silurian are represented by
Climatius ornatus and Parexus recurvus, while with these
in Forfarshire occur two types of Myriapod, Kampecaris
forfarensis and Archidesmus sp.

In Silurian and Devonian Epochs

119

In beds higher than these apparently, that Goodchild
calls the Orcadian, he and Flett have made known a rich
series of fishes that suggest a gradual splitting up, and
evolution of older types, into the two great elasmohranch
and ganoid groups of succeeding formations. Also while
some genera, like Coccosteiis (Fig. 9d), extend through
the entire series, others are typical of, or even extremely
abundant in, definite strata. The following is a partial

Fig. 9. Fishes of the Old Red Sandstone (Devonian) period-
a Cephalaspis lyelli (after Lankester) ; b, Osteolepis microlepi-
dotiis ; c, Dipterus valenciennesii (both after Traquair) ; d, Coccos-
teiis decipiens; e, Acanthodes mitchelli (after B. N. Peach). All
reduced from A. Geikie.

I20 Evolution and Distribution of Fishes

list of those recorded: Tristicoptenis alatus^ Diptenis ma-
cropterus and D. valenciennesii (Fig. 9c), Microbrachius
dicki, Homosteiis milleri, Coccosteiis decipiens and C.
minor, Diplacanthus striatus, and D. tennhtriatiis, Mesa-
canthus peachi, Cheiracanthiis murchisonii and C. latiis,
Glyptolepis paucidens, Gyroptychius microlepidotus,
Osteolepis microlepidotus (Fig. 9b), and macrolepidottis,
Thursiiis macrolepidotiis and T. pholidotus, Diplopterus
agassizii, Mesacanthus pusilliis, Pterichthys milleri, P.
productus, and P. oblongus, Cheirolepis trailli, Glyptopty-
chius angiistus and Parexus sp. These deposits therefore
are rich alike in individuals and species.

While the remains of these fishes are often scant or
absent from the coarser sandstones or shales, they may
be crowded in countless numbers in the harder shales and
flagstones. Flett says (22:383) that these "calcareous
and bituminous flags -are the chief receptacles of the fossil
remains enclosed in these rocks. The fossil collector very
soon learns that the best specimens are obtained in a brittle
hard, usually slaty and thin-bedded rock, which rings to
the hammer like a piece of metal. This is in some measure
due to the compactness and impermeability which is con-
ferred on these rocks by their abundant calcareous matter."
Though this type of rock might quite be a fine argillaceous
lacustrine or fluviatile deposit, that afterwards became
baked, the writer cannot but suggest that such may rather
have been due to deposit of volcanic dust that suddenly
killed, covered up, and permeated the armor of each in-
dividual. Favoring this is Flett's observation: "it would
seem as if these species had been unsuited to the new
environment in some manner or other, and their extinction
had been rapid and complete. The flags so crowded with
fossil remains of Diptenis valenciennesii — only a few of
which have attained their full size — irresistibly impress on
the mind the idea of a sudden extermination." Other
writers express a like opinion.

The unconformability noted by Geikie and his succes-
sors, between deposits of the Lower and Upper Old Red
rocks, must represent a considerable lapse in time. But
before treating of this it may be opportune to observe,

In Silurian and Devonian Epochs

121

that the evolution of fishes up to this stage doubtless con-
sisted in the appearance of groups of soft-bodied scaleless
animals with cyclostome affinities, of which the remarkable
Palaeospondylus gunni (Fig. lo) from the Old Red rocks

of Caithness is the only known
illustration. Alongside such
there evolved — probably from
a Thelodus-like ancestry — the
sluggish, toothless, and heavily-
armored bottom-feeders, that
have been included in the great
group Ostracodermi. These
reached their climax — alike as
to structure and abundance of
Individuals — in the late Silurian
times, and were becoming rare
or extinct in early Old Red age.
But meanwhile, evolving from
a Birkenia-Lasanius ancestry of
Silurian age, the more lithe
forms that were ancestral, in the
writer's estimate, to the ganoids
and elasmobranchs, were in-
creasingly asserting themselves,
and became dominant in fresh-
waters of the Lower Old Red
period. So it should be special-
ly emphasized that the fore-
runners of all the later Selachi-
ans were of freshwater origin.
On the European continent,
however, an apparent exception
to the above has greatly puzzled
the writer. For Schliiter and Traquair {77: 723) have de-
scribed the heterostracous genera Drepanapis and Phlyctae-
naspis from the Hunsriicken slates of Gemiinden. These
genera are asserted to be in direct association with crinoids,
starfishes, trilobltes, bivalve and cephalopod molluscs. This
causes Traquair to declare : "It is perfectly clear from the
contained Invertebrate fossils that the Hunsriick slates are

Fig. 10. Restored figure
of skeleton, Palaeospondylus
gunni. c, calcified cephalic
cirri; pa, auditory capsule;
tp, supposed nasal capsule;
X, postoccipital plate. (After
Traquair.)

122 Evolution and Distribution of Fishes

of marine origin, and consequently that their "mailed" fishes
were inhabitants of the sea. This is however not strange
when we remember that mailed fishes {Pterichthys, etc.)
also occur in the Middle Devonian Limestone of the Eifel,
in company with such purely marine fossils as crinoids and
brachiopods." The writer might advance possible explan-
ations regarding the above undoubtedly exceptional rela-
tions, but would preferably desiderate a more critical study
of the rock-successions in connection with their contained
fossils. That the organisms thus grouped together, lived
in distinct freshwater and marine environment, seems to
the present author assured.

The Upper Old Red rocks of Europe are represented
over a wide range of country from South-east Ireland across
Central Scotland to Norway, Russia, and probably even
Spitzbergen. So this range would include a considerable
part of Freeh's Arctic-Atlantic continent. The strata are
on the whole of a lighter color than the lower Old Red
rocks, though ferruginous red predominates. The richest
fossiliferous rocks are also here of a hard fissile argillaceous
or argillo-calcareous type, that might again suggest rapid
deposition of volcanic dust. This is eminently true of the
celebrated "cyclopteris" or Kiltorcan rocks of South-east
Ireland and of northern Scotland. From these areas large
and beautifully preserved leaves of Palaeopteris {Archae-
opteris) , stems of Knorria, Calamites, Lepidodendron and
other drifted land plants have been abundantly secured.
In Ireland the freshwater lamellibranch Anodonta jukesii
is associated with these. The freshwater phyllopod Es-
theria membranacea is still abundant, and in this con-
nection no palaeontologist has been a more consistent and
yet unconscious advocate for the freshwater habitat of
primitive fishes than Rupert-Jones. Thus, in recording the
finding of Estheria by C. W. Peach in three quarries in
the parish of Wick (ySiii) he observes that "Dipterus,
Diplopterus, Osteolepis, Glyptolepis, and Coccosteiis with
land plants are also found in these quarries," and he ac-
companies this with such statements as: "In the Estherian
flagstones of Caithness we have no evidence of any marine

In Silurian and Devonian Epochs 123

characters, nor does their being associated with some
thousand feet of sandstones and conglomerates render it
impossible that they themselves should have been formed
in freshwater or brakish water." But his subsequent re-
marks indicate that his mind was in a somewhat uncertain
state.

On page 16 he makes the very significant observation
that the Estheria tests "are found in a thin bed, and lie
in great quantities on the surface planes, never to any
depth, but just as it were interleaved. Here, as well as
at all the other localities, they are accompanied by scales
of fishes and pieces of bone." Now, from direct observa-
tion by the writer on the deposits of mud and sand over the
wide flood-plains of Southern States rivers, from our
knowledge of the greatly more extended periodic river-
floods of the Orinoco, Congo, and other continental rivers,
the above observation suggests that each "thin bed" of
Old Red rock, represented a periodic flood deposit, and on
retreat of the waters shallow marshy areas were left in
which, as with present-day Estherieae, the tiny organisms
multiplied prodigiously. When the next succeeding per-
iodic inundation took place, fish scales and bones, plant
remains and other organic debris would be deposited, suc-
ceeded by a new "thin bed" of mud or fine sand that sealed
up the Estherieae "in great quantities on the surface
planes." This is in line also with Barrell's contention (79 :

33S)-

Here it may appropriately be added that Jones ob-
tained specimens of Estheria inembranacea from Livonia
in Russia, and says (p. 18) "these are identical with the
Estheriae from Caithness." Also (p. 20) "on the river
Torgel in Livland Dr. Pander found that the hard white
sandstones used for grindstones, contain fine remains of
Asterolepis (Pander) and that the overlying bluish marls
and clays contain scales and teeth of Osteolepis, Dipterus
and Glyptolepis in company with Estheria membranacea."

The fish fauna of the Upper Old Red rocks is a varied
but steadily evolving one. In addition to clumsy heavily-

124 Evolution and Distribution of Fishes

Fig. II. Bothriolepis canadensis, dorsal surface, about three-
eighth natural size. (After Patten).

armored members of the Antiarchi like Bothriolepis (Fig.
1 1 ) and Asterolepis, or of the Arthrodira-like Coccosteus
and allies, that persist from lower Old Red strata, though
altered in the representative species, the rather more agile
and still existing Dipneusti are now represented by Phan-
eropleuron (Fig. 12.) and Palaedaphus, as compared with
Dipterus of the lower rocks. But the crossopterygian group
is now a prominent one, and in such genera as Holopty chins,

In Silurian and Devonian Epochs 125

Dendrodus, Glyptoponms, and Glyptolepis the formation
can be widely recognized over the entire "Arctic-Atlantic"
area. The numerous species described by Traquair (Lank-
Traq. in Palaeon. Soc. 1868-19 14) indicate a still greater
wealth for the future. The suggestive couple of papers
by Barrell (79:345,387) emphasize somewhat strongly a
fluviatile rather than a lacustrine origin for many of the
Old Red beds. And unquestionably if one considers flood-
plain possibilities, the areas of fluviatile deposition may
have been extensive. A combination, however, of fluvia-
tile, of lacustrine, and of fluvio-lacustrine flood-plain sed-
imentation seems better to explain the requirements of the
case. The valuable observations also of Rogers {81:100)
for North Devon, and of J. W. Evans (^2:547) for
North and South Devon, as for South Wales and Southall,
suggest that the area once covered in Britain by Upper
Old Red deposits may have been considerable.

Fig. 12. Phaneropleuron andersoni, a primitive dipnoan fish
from Upper Old Red rocks of Scotland, about one-third natural
size. (From Traquair-)

As to the wide range of the fishes, A. S. Woodward
writes thus (Proc. Geol. Assoc. 18 (1904) 433) : "It may
be said that Holoptychius and Sauripterus (or Crossop-
terygian genera of equal rank) with Bothriolepis and
Asterolepis characterize the Upper Old Red Sandstone
or Upper Devonian wherever it occurs — in Britain, Belgium,
Germany, Russia, Spitzbergen, Greenland, Canada and the
Catskills of New York. All assertions to the contrary
are based on a wrong interpretation of the fragments,
by which alone the fishes are so frequently represented."

Turning now to the Devonian, Erian, or Old Red sys-
tem of North America we seem here to encounter a fairly
even continuity, but likewise alternation, in the Devonian

126 Evolution and Distribution of Fishes

or marine and the Old Red or freshwater rocks. This
seems also to be confirmed by the close identity of the
fauna, though, as might be expected across so wide an
extent of country and stretch of time, some very different
and even remarkable types are here met with.

Reference might now be made to the excellent con-
densed description of the formation given by Chamberlin-
Salisbury ((5*: 418). There a division into palaeo- meso-
and neo-devonic is accepted from Clarke and Schuchert.
An examination of these subdivisions, and of their con-
tained fossils, demonstrates that steady alternation, of
freshwater or land surfaces with littoral or deep-littoral
marine areas, took place.

Further in the exhaustive studies that have been made
of the latter by Newberry, Orton, Clarke, Hayes, Prosser,
Meek, Worthen, Williams, Gregory, Weller, Fuller,
Ulrich, Schuchert and many others, the fauna recorded
is uniformly and consistently marine, while it stands out in
sharp contrast with the results to be recorded below. But
in saving this, exception must be taken to some of the pio-
neer work of such distinguished palaeontologists as the
earlier leaders of the Ohio survey. Thus in the graphic
— though as we would Interpret conditions the entirely mis-
taken — word pictures given in Vols, i and 3 of the Ohio
survey, {8^:26^; 5^:603) extensive ocean-stretches are
put before the minds eye, as being peopled by an abundant
marine fish fauna.

But when we correlate carefully all the Information
since gained regarding the Old Red rocks of Ohio, and
compare such with 'the descriptions In the above-cited vol-
umes, as well as the rock section given in V.3 (Geology)
p. 604, instead of regarding all of the rocks as having been
deposited In "an ancient sea," or as being "an open-sea
deposit," the writer would accept that the lowermost rocks
in the Corbin's Mill section which contain flinty nodules,
or which are fossiliferous and abound in brachlopods, marine
gasterpods etc. are truly marine. But he would emphatical-
ly claim that the "shaly limestone," which not unfrequently
contained wood of a species of ancient pine {Dadoxylon
newberryi Dawson)^ tells of lacustrine or flood-plain con-

In Silurian and Devonian Epochs 127

ditions. When further a bone-bed occurs just above, that is
"a six-inch layer" and is crowded with fish remains, we
would again claim that this represents a sudden volcanic
dust deposit, that killed and in a few days entombed the
surrounding fishes over hundreds of miles. This again
was succeeded by a blue limestone that closely resembles
freshwater limestones of Europe. Orton says of this: "the
fossils of the Delaware beds are at this point chiefly fish-
remains. Teeth, plates, jaws and other bones are not un-
frequently met with throughout 25 ft. of this series." But
he does not account for the great abundance of these, nor
for the total absence of undoubted marine organisms, if
the deposit was laid down in "an ancient sea."

It would be a premature task as yet to attempt any
correlation of the deposits as treated by Orton and others.
The palaeontological researches however of Hall, New-
berry, Dawson, Claypole, Clarke, Whiteaves, Matthew,
Traquair and Eastman, indicate three fairly sharply-marked
groups of freshwater strata, intercalated between others
that are marine.

The lowermost beds of the formation in the central
Eastern States, consist of the Helderbergian and Oriska-
nian. These are wholly of the marine type, and yield an
abundant invertebrate marine fauna, though no marine fish
remains, where accurate record of beds has been made.
But probably deposited synchronously with them, though
in freshwater areas, are the Canadian beds, that are often
called the Gaspe and Campbellton. The included fishes are,
in their affinities, a curious blending of the European Upper
Silurian and Lower Old Red. Thus there are abundant
examples of Thelodus (Fig. 8a), several species of CepJial-
aspis (Fig. 9a), and from the lower-most beds Asterolepis
clarkei, all of these being of Silurian-Devonian age and of
agnathous structure.

But with them are Acanthodes semistriatiis and Cltmat-
ius latispinosus representing primitive selachians; spines
of the probably allied selachians Homacanthus and Macha-
eracanthus, the arthrodire Phlyctaenaspis acadica — a close
ally of Coccosteus — and isolated teeth of Dendrodus.

128

Evolution and Distribution of Fishes

Flourishing with the above, but as land dwellers Daw-
son {8j: 523) has described various eurypterids, species of
insects, and an abundant flora that included Calamites,
Lepidodendra, numerous species of fern, the specialized
genus Cordaites and other less certain types.

Succeeding to the above, and during mesodevonic times,
an extensive tract of palaeodevonic sea-bottom became ele-
vated over a wide extent of New York and Pennsylvania,
westward to Illinois and Iowa. This became peopled with
a flora and fauna that approximated to the lower part of
the European Old Red Sandstone, but which includes some
striking intrinsic types. This is the Onondaga, Ulsterian,
or Corniferous limestone area above referred to. In ad-
dition to three species of Coccosteus, remarkable allies of
it are Dinichthys with jawbones (Fig. 13) about two feet
in length, Protitanichthys, Macropetalichthys, and Aster-
osteiis.

Fig. 13. Dinichthys hertzeri.. Upper figure shows view of jaw-
bone from inner side, lower figure from outer side. (Reduced from
Newberry.)

Now Newberry, in his elaborate palaeontological re-
ports, takes it for granted throughout that these were
marine fishes and of marine origin. Thus, to quote only

In Silurian and Devonian Epochs 129

two passages, he says {86:24): "The bone-beds of the
Corniferous Limestone, in which the remains of millions
of marine fishes (ital. author) of Middle Devonian age
are strewed over the old sea-bottom, contain numerous stud-
like, often highly ornamented dermal tubercles, and occa-
sionally fragments of the pectoral spines of Machaeracan-
thus, but almost no teeth of cartilaginous fishes." And
on the succeeding page he says: "The derivation of this
fish-fauna is not known to us. The Devonian Cephalaspidi-
ans, Cephalaspis, Acanthaspis and Acantholepis have afilini-
ties with Pteraspis and Scaphaspis of the Upper Silurian and
are perhaps their descendants, but the origin of the most
striking and characteristic elements in this fauna — the
gigantic Dinichthidae and the scaled and plated Ganoids,
Onychodus, Macropetalichthys and Asterosteus, as also the
great pterichthid Aspidichthys and the Elasmobranchs
Rhynchodus and M achaeracanthus , among the largest and
most highly specialized of all fishes — will perhaps always
remain a mystery. Most of these were inhabitants of the
Corniferous sea, and came in from the great oceanic basins
with the flood which, at a certain time, inundated parts of
the North American continent and deposited upon them
the sediments which we call the Lower and Middle Devo-
nian rocks."

Then on page 30 he suggests that the entire bone-bed
"accumulated in some nook or bay, perhaps bordering a
coral reef where large and small fishes congregated age
after age, until their Kjokkenmoddings formed a sheet
some inches in thickness over all the sea-bottom." Now the
remarkable feature is that neither Newberry nor subse-
quently Orton in "Palaeontology of Ohio" describe a single
coral or other marine organism from the bed. Claypole
again (^'7:313) in his paper on "The Devonian Era in
the Ohio Basin" says: "Apparently the fishes of the Cornif-
erous were tenants of the open sea and the clear water,
where dwelt the coral polyps, and where the deposits were
limestone." In the entire absence of traces of the corals,
in the presence toward its base (p. 316) of "masses of
silicified wood (Dadoxylon newberryi Dawson)," and in
the occurrence of similar fishes in Europe alongside remains

130 Evolution and Distribution of Fishes

of a land vegetation, we are forced to conclude that the
Upper Cornlferous of the Middle Devonian was of fresh-
water origin, unless weighty arguments to the contrary can
be adduced.

But undoubtedly a mixing of lists of fossils, from closely
placed beds or laminae, some of which were of marine,
some of freshwater origin, has frequently taken place for
Ohio. Thus the recording of Lingula and Discina with
fish remains, while perhaps rarely indicating rapid changes
in the relation of sea and land, is accurately and readily
explained by the more recent studies of C. S. Prosser
(5^:297) on "The Sunbury Shale of Ohio," where he
shows that only fish remains occur throughout one bed,
while the above-named brachiopods are found abundantly
at the base of the bed where change was proceeding. They
are 7iot mixed together.

As Whiteaves and Eastman have pointed out, a wide
extension of this series of beds, with similar fish-remains,
was continued into Hudson's Bay {8g: 191), and on p. 193
he shows the close resemblances of the strata there to the
Eifelian deposits of Bohemian and Russian Central Europe.

During deposit of the Huron and Hamilton shales and
limestones, the sea again encroached at least in some areas,
and this period marks the transition from a Mid to an
Upper Devonian fish fauna. So when land elevation again
took place, and freshwater conditions were reestablished,
deposits over extensive areas of rocks with contained fish-
remains, were laid down, that extend westward from New
York and Pennsylvania through Ohio to Iowa and Colo-
rado. These form the Catskill and Cleveland series. The
abundance and rich variety of this Upper Devonian Fish
Fauna is demonstrated in the lists given by Claypole for
Ohio (57:318) and by Eastman generally (op. cit. pp. 24-
172). Thus the former lists fully a hundred species from
the Ohio shales. For the New World as for the Old there-
fore, this period was evidently the one when fish-life was
dominant and prodigiously abundant in freshwaters, though
— so far as exact evidence goes — was wholly or almost
wholly absent from the sea.

In Silurian and Devonian Epochs 131

A somewhat related fish-fauna Is that from Scaumenac
Bay and other parts of Canada, but so far as it is now
known, it did not include such gigantic forms as Dinichthys
and Titanichthys. Eastman's condensed list {Sg-. 16, 17)
is as varied as it is suggestive.

In North America, as in Europe, the fossilized fish-
fauna of the Upper Devonian is nearly always associated
with beds that are rich in eurypterids, in phyllopods, in
highly evolved scorpions and myriapods, In a characteristic
mollusc, and in finely preserved specimens of ferns and
lepidodendrold plants. These have been described or re-
ferred to by Dawson, Newberry, Claypole (op. cit. p. 342),
Patten {10: 2,11) and others. More than passing mention
however should be made of "a freshwater mollusc."
Originally named Anodon jiikesii by Edward Forbes, its
history and biological environment have been ably traced
by R. B. Newton (90:245) who named it Archanodon
jukesii. He points out that Forbes found with it, at Knock-
topher in Ireland, remains of the eurypterid Pterygotus,
of the fish Holoptychius^ also the Upper Old Red plants
Cyclopteris, Archaeopteris (or Palaeoptens) hihernicus,
Lepidodendron, and Stiginaria. Subsequently commented
on by Baily, Jukes, Hull, and Boyd Dawklns, it was by the
last compared with Cypricardites catskUlensis a* closely
allied form from Chenango County, New York State. In
Ireland as in America similar envlronal conditions evidently
prevailed, for he writes: "In Ireland the mollusc occurs
with Palaeopteris hibernica etc., Coccosteus etc., and
Eurypterus scouleri? etc; in Northumberland with Uloden-
dron ornatissimiivi and Calamites ; and in America A. cats-
kUlensis, the close ally of the British species, is found in
company with plant and fish remains {Holonema riigo-
stim) ." Here then we have a glimpse of a freshwater
biological grouping that must have been more or less con-
tinuous from England to America.

So he concludes: "All these facts demonstrate that the
genus Archanodon was of lacustrine or fluviatile origin,
and that the deposition of the beds containing It, whether
in England, Ireland or America must have been regulated

132 Evolution and Distribution of Fishes

by similar physical conditions, and in close proximity to
land."

The most recent and remarkable additions to our knowl-
edge regarding the distribution of Devonian fishes are due
to material secured by the Arctic "Fram" expedition of
Nansen, and by the "Terra Nova" expedition to the Ant-
arctic. The fossils from the former region were secured
by Dr. Schei at four localities round the upper end of Goose
Fiord in EUesmere Land, and on his death were described
by Kiaer {gia: i). The rocks evidently belong to the
"uppermost member of the Devonian," and consist of red
and gray sandstones, sandy and micaceous schists, "anthra-
cite in strips and thin layers," also at three of the four
localities of "bituminous layers in the light gray sandstone."
The richest locality yielded "a quantity of mussels, numer-
ous fish remains, and indeterminable fragments of plants."

Two species of Psammosteus, one of Bothriolepis,
Holoptychius scheii, a Glyptolepis that is possibly identical
with G. paucidens, and a species of Osteolepis, together
indicate Old Red freshwater deposits that had been laid
down in waters which must have been more or less con-
tinuous from Russia, Scandinavia, and Scotland westward
to the central and arctic parts of the North American
continent.

Still more recently A. S. Woodward has published
in the records of the British Terra Nova Expedition {gib:
51) a paper that opens up new and striking suggestions
as to the distribution and environment of some Old Red
fishes. For in "Fish Remains from the Upper Old Red
Sandstone of Granite Harbor, Antarctica" he has been able
to identify the following:

Antiarchi Crossopterygii

Bissacanthoides debenhami Holoptychius antarcticus

Bothriolepis antarctica Osteolepid

Elasmnbranchii . •

L heir acanthus sp. ^ f^.

Dipnoi Palaeoniscid.

Fragments of Coccosteus

The existence of the above fishes in palaeozoic rocks near
the South Pole, opens up many puzzling problems. But
Granite Harbor is south from Australia, though nearly

In Silurian and Devonian Epochs 133

3000 miles removed, and it is from Australia that primitive
Carboniferous fishes have been obtained. The genera how-
ever of these are the same as those recorded from India,
Russia, Scotland and N. E. America, and all are of fresh-
water habitat. Six also of the above-named genera were
first found in North Europe, so that a possible generic
distribution, almost from pole to pole, during Old Red and
Carboniferous times, seems to be indicated, and this by
way of Eastern Australia. With the above two papers
before us the conclusion then seems sound, that from near
the North Pole to near the South Pole an extensive area
of land once existed, the lakes, rivers, and flood-plains of
which harbored related genera and even allied species of
fish. These were so numerous that abundant remains of
them are now being laid bare from widely apart centres.

The map that forms Fig. 15 (p. 136) suggests possible
land areas during Upper Old Red and Carboniferous times.
The land areas however may have been greater.

As to the food and mode of feeding of the Silurian and
Old Red fishes, all evidence indicates that the Agnatha were
devoid of teeth, and were "bottom-feeders." Again the
primitive dipneustians like Coccosteus, Macropetalichthys,
and Dipterus were wholly devoid of ordinary cutting teeth,
and only had broad tubercled crushing plates in the lower
palate. So these resembled, but were more primitive than,
the similar plates of such a living dipnoan as Neoceratodus
of Australia. Now we know that the three living dipnoan
genera {Neoceratodus^ Lepidosiren, Protopteriis) feed
largely on aquatic vegetation, but also in part on small
freshwater animals. The frequent accumulation of crushed
vegetable remains, or of teeming masses of phyllopod crust-
aceans, alongside these primitive fishes, would indicate that
they, like their existing dipnoan descendants, were largely
herbivorous, possibly to a less degree dependent on small
and soft animal prey.

The appearance of chondrostean types like Cheirolepis,
and of crossopterygian types like Osteolepis and Megal-
ichthys with dentarian teeth of small to moderate size, sug-
gest the catching of small prey, as is true of their nearest
descendants of to-day.

134 Evolution and Distribution of Fishes

But the gradual evolution of Onchiis and Cladoselache,
of monacanthid and diplacanthid forms, that seem all
to be primitive selachians, from the late Silurian to the
close of the Old Red period, introduces a new and more
voracious type of fish. For while in Cladoselache and
Acanthodes, the teeth are of variable size, form, and adapt-
ability for grasping or tearing, in genera like Ischnacanthus
and Acanthodopsis they are strong and adapted for grasp-
ing prey. Their further striking evolution along increasing-
ly carnivorous lines will be traced, when we reach the next
great geologic period.

In shortly reviewing now the Old Red Sandstone period,
we would regard this as the contemporaneous and fresh-
water geologic representative of the Devonian or marine
set of rocks, though in recent years the term "Devonian"
has been often applied to both. During deposition of these,
varying oscillations took place in the relation of the land,
of freshwater, and of marine areas. But throughout the
period a huge and practically continuous northern continent
— the North Atlantis of Freeh — was developing a rapidly
advancing plant and animal life. For to find Holoptych'nis
giganteus in Upper Old Red rocks of New York, Pennsyl-
vania Iowa, and Colorado, in the north of Scotland, in
Belgium and in West Russia; to find //. nohilissimus and
H. flemingi (Fig. 14) with a like Old World distribution;
to find closely related species like H. halli, and H. america-
niis along with H. giganteus in rocks ranging from New
York to Colorado, indicate a community of environal con-
ditions that must have been extensive and intercom-
municating.

Fig. 14. Holoptychius flemingi. A crossopterygean fish from
Upper Old Red rocks of Scotland. About one-eighth natural size.
(From Traquair).

In Silurian and Devonian Epochs 135

So while in the seas and along the shores of that north-
ern region, a teeming invertebrate fauna existed, that was
rich in corals, echinoderms, brachiopods, and molluscs, ex-
tensive freshwater lakes, rivers and swamps developed and
sheltered myriads of phyllopod crustaceans, of eurypterids,
of bivalve molluscs, and specially of fishes, that attained at
times to huge size and formidable defensive armature.
While some of these like Cephalaspis, Bothriolepis and
Euphanerops have left no living descendants or representa-
tives, others belonged to elasmobranch, dipnoan, or ganoid
groups that are still alive in derivative types.

Contemporaneous with these on land areas and often
washed into the freshwater deposits to be preserved there,
were scorpions, myriapods, and insects, as well as a varied
vegetation, many members of which had reached to a high
stage of lepidodendroid, equisetoid, or pteridoid organiza-
tion. This freshwater or land flora and fauna have been
made known to us, in part by preservation in or between
successive deposits of mud, lime, or sand that were laid
down during periodic freshets which affected lake, river and
flood-plain areas, in part by rapid deposit of volcanic dust
or other debris laid down during or soon after widespread
volcanic activity. This destroyed coi^ntless myriads of
organisms, not least of fishes, whose hard parts occur often
in "bone-beds."

The question of mineral-oil or petroleum production
has already been treated (pp. 49-59), but we would here
emphasize that as the climax of fish-evolution in number
of individuals and wide community of species had now been
reached, so it is from these strata that the richest and most
valuable supplies of mineral oil have been secured in the
latter half of the past century. Such we would attribute
almost wholly to the volcanic destruction and rapid entomb-
ment of myriads of fishes.

Finally before passing to the next great formation,
we would direct attention to the diagram of possible con-
tinental relations that existed during the late Devonian and
Carboniferous periods (Fig. 15). This sets forth details
that seem to be needed in explanation of the evolution and
distribution of ancient fishes of that time. Wide continuity

136 Evolution and Distribution of Fishes

Fig. 15. Chart showing possible outlines of land, by shaded area, as existing
in late Old Red or Devonian, and in Carboniferous times. Such is indicated by
the distribution of plants, also of freshwater fishes and other animals.

and extension of the continental masses of the earth are
indicated alike over the northern and the southern hemi-
spheres. Only thus can one properly explain the continuous
range of dipnoan and crossopterygian types in the fossil
state; the early and continued residence in America and
Australia of types of these or of their descendants; also
the lingering existence of the three genera Neoceratodus,
Protoptenis, and Lepidosiren in Australia, Africa and
South America respectively. If we accept compactness in
the land-masses of the globe at this time, it aids in solution
of many problems.

In Carboniferous and Permian Epochs 137

CHAPTER V.

The Physical and Biological Environment of Fishes.
(b) During the Carboniferous and Permian Epochs.

In the Carboniferous and Permian as in the Siluro-
Devcnian systems freshwater and marine strata, both
often of great thickness, have to be distinguished, though
it is difficult as yet to correlate these exactly over the world.
But in the Northern Hemisphere, over a great part of
Europe and North America, probably also of Russian
Siberia, a fairly continuous land-area must have persisted
from "Old Red" times. For only thus can we interpret
the plant and animal organisms encountered in the rocks.
Here also it may at once be emphasized, that during the
Mid-Carboniferous — possibly somewhat earlier — we first
trace the invasion of marine areas by evolving lithe fresh-
water fishes belonging to the great elasmobranch series.
But a truly remarkable feature is that these become practi-
cally exterminated again over such areas, in late Carboni-
ferous or in early Permian days.

In the Carboniferous formation as a whole, two im-
portant groups of rocks are largely — often wholly — of
freshwater or land origin. The lowermost of these has
been variously called the Culm, Calciferous Sandstone,
Misslssippian (In N. America) or Lower Carboniferous,
and its beds evidently extended continuously from Central
North America, eastward through north Britain and
France, to Mid Germany and Mid Russia. Chronological-
ly this series seems to have been formed over the North
Atlantic and Nearctic continents of Freeh — both of which
must have been more or less continuous as Indicated by
him — at a time when further south In Europe, and also in
North America, the marine beds of the Lower Carbonifer-
ous or Misslssippian, were in process of deposition. So
while the latter contain a great wealth of typical marine

138 Evolution and Distribution of Fishes

invertebrate — rarely fish — organisms, the former indicates
largely or wholly freshwater conditions.

But while in some localities or regions there seems to
be direct conformability and therefore continuity, from the
top of the Old Red to the base of the Calciferous or Missis-
sippian, in other cases a considerable period must have
elapsed, when terrestrial denudation and environal changes
were proceeding. That profound changes in the relation
of land and sea were also in progress is evident, and is al-
most certainly to be explained by the frequent volcanic out-
bursts, accompanied by extensive deformation and faulting
of strata through earth shrinkage. Regarding such Geikie
says: "One of the most singular features of the Lower
Carboniferous rocks of Scotland is the prodigious abund-
ance of the intercalated volcanic rocks," and he distin-
guishes two great types of these, ( i ) the plateaux "where
the volcanic materials were discharged so copiously that
they now form broad tablelands or ranges of hills, some-
times many hundreds of square miles in extent, and 1500
feet or more in thickness;" and (2) puys or vent-cones
where small and local amounts of lavas, and more copious
showers of ash were thrown out. Such must undoubtedly
have caused widespread destruction to animal and even
to plant life, while it gave occasion later for evolving and
commencing new types to multiply and spread abroad.

The writer spent the leisure time, during years of his
earlier scientific career, in tracing these Calciferous rocks
over extensive tracts of the Forth basin, and as already
noted he was constantly impressed by their predominant
freshwater character, as well as the great thickness of the
strata involved. Composed of varying beds of sandstone
that were of a reddish-yellow or white color, of hard black
fissile shale, of softer argillaceous layers, of extensive fresh-
water limestone beds, or of brown-black bituminous oil
shales, these all yielded a greater or less abundance of
associated plant and animal remains. But as the writer
has already shown, in unravelling the history of Lepido-
phloios {g2: 181), it often happened that the bulkier por-
tions of some plant might be found in one set of beds,

In Carboniferous and Permian Epochs 139

usually the finer sandstones; the smaller and lighter plant
parts or the larger fishes in another, often the bituminous
shales; while delicate twigs, expanded "fern" fronds, and
small fishes might be spread out over the thin laminae of
black fissile shale.

As Stur, B. Peach, Traquair, Kidston and other palae-
ontologists have shown, the biological assemblage of organ-
isms is typical. Thus the writer has often laid bare from
adjacent parts of the hard yellow-white limestone of Burdie-
house, a jaw with huge glistening brown-black teeth of
Rhizodiis hibbertii, myriads of the minute phyllopod
Leperditia okeni var. scotobiirdiegalensis, delicately ex-
panded leaves of Sphenopteris affinis, S. hoeninghaiisii, or
S. bifida, the sporangiferous cones of Lepidodendron and
Lepidophloios, fragments of Eiirypteriis scouleri, and not
infrequently somewhat crushed but entire specimens of such
freshwater fishes as Elonichthys robisoni, E. biicklandi,

Fig. 16. Eurynotiis crenatus, a common actinopterygian ganoid
fish from the Calclferous or Lower Carboniferous beds of Mid-
Scotland. About one-fourth natural size. (Restored by Traquair.)

Rhadinichthys ornatissimiis or Eiirynotiis crenatus^ (Fig.
16) . And for exact identification the latter usually passed
under the master eye of Traquair.

The marked agreement between the flora — and such
also we know to be true of the fauna — of the Calciferous

140 Evolution and Distribution of Fishes

series in the Forth basin and that of the "Culm" In east
central Europe as elucidated by Stur, was first indicated
to the writer by the veteran naturalist C. W. Peach, fully
forty years ago. This demonstrated an organic continuity,
as there doubtless was a geographic. But Heer has de-
scribed {gs : 161 ) an interesting set of beds in Bear Island,
that seem equally in their plant and animal organisms to
extend the Calciferous formation into far northern regions,
and also to relate it with the Upper Old Red of Europe
and Canada.

Here it might be said that mixed or truly estuarine con-
ditions are of minor account and of doubtful identification,
though their supposed widespread existence in the past has
been extensively used by palaeontologists to explain puzzling
combinations. It is the difl^culty of reconciling such an
abundant fish-fauna as that of the Carboniferous system,
with life in wide freshwater areas, that often caused so
painstaking an observer as Traquair to postulate or tacitly
accept a marine or at least an estuarine environment, when
most or all of the facts in view favored a freshwater ex-
istence. It Is, we believe, this restricted attitude of mind
that caused him to think of localized estuaries, rather than
of connected continental masses, and so caused him to
overlook the great value biologically of what he so often
and wisely pointed out, viz. the wide distribution of some
species or genus over different lands, and the Invariable
association of such with certain phyllopods, eurypterlds,
scorpions, freshwater molluscs, and — not least — of like
genera or even species of plants.

It Is this failure also to realize that fishes were largely
at this time, and previously had been wholly, land-locked
animals of freshwater habitat, and that were undergoing
wide intercontinental evolution, which caused him to pen
the following (77:707) : "We have in the estuarine beds
of the Lower Carboniferous series of the central valley
of Scotland, a fish-fauna of which many of the species per-
sist through thousands of feet of strata, and must therefore
have lived for a very long time without change in their
specific characteristics. Then, after the Millstone Grit,

In Carboniferous and Permian Epochs 141

poor in fish remains, is passed, we come to a new fauna,
from which nearly all of the Lower Carboniferous species
and with them also a number of genera have disappeared,
their place being taken by an Upper Carboniferous assem-
blage, which in its main features is characteristic not only of
the Coal Measures of Scotland, but of the Lower and
Middle Coal measures of England, extending also into the
transition series of the latter country."

Long-continued and increasing environal changes in the
wide continental areas inhabited by the two groups of fishes
he here compared, could only result in a changed facies of
the species he refers to. In this connection Rupert-Jones
very neatly remarks : "All animals may have been marine,
subsequently brakish or freshwater, and this may have
been the case with Estheria^ but except for the progressive
aspect of the argument, the converse might just as well hold
good for the Lingiila^ the Spirorbis, Avicida, Anthracosia,
Anthracomya, and Pleurophorus, mentioned as being found
in the older rocks in company with Estheria."

What actually happened for fishes is fully set forth in
a succeeding chapter. Here it may shortly be said that
while the ganoids, crossopterygians, and not a few elasmo-
branchs remained in their former freshwater habitats, a
gradual migration of some lithe, predaceous and powerful
elasmobranchs into the sea took place during late Upper
Old Red or more likely during Lower Carboniferous time.
Then, and then only, their remains begin to appear along-
side typical invertebrate marine forms, and this condition
persists into the Upper Carboniferous or even Lower
Permian.

As to the nature and successional relation of the chief
fossiliferous beds of the Calciferous series round Edin-
burgh, the accompanying table (Fig. 17) from one of
Traquair's extensive papers (77: plate i) will illustrate,
while it also sets forth the thickness of the beds. From a
fairly intimate acquaintance with them the writer would re-
gard the Craigleith sandstones and Wardie shales, the
Burdiehouse limestone, the uppermost "Oil shales" and all
of the connecting beds between these as purely freshwater,

142 Evolution and Distribution of Fishes

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Depth

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1538
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Bed. SandstOTies if: Shales.

Sandstones, Shales,
FireclcLys, Coals tt
IroTVStoTies .

SandstoTies, Fireclays &c.

N?6 LIMESTONE, "lEVENSEAt"

N95 LIMESTONE, "cALMY',' ARDEN"or "gAIR'

Sandstones, STudes, & thin Coals

N?* LIMESTONE, "index"

I Sandstones, Shales, Firedaj's ,
Coals & Jronstojies.

HOSIES"
N° rtlMESTONEj ■'giLMERTON"or "hL

SaruLstoTies & Shales
Oil Shales

COAL

Marls

\ COAL "HOUSTON"

Sandstones, Shales & OilsTiales
Oil Shale "Tells"

BroociuriL Afarl.

Upper limestone

GROUP

COce COALS

I LOWER LIMESTONE
J CROUP

Oil Shale Sroxium"

JBinnej' SandstOTie

Oil Shale ^JhaiTLet!'

Sandstone & Fine Con^loiru^rale ,

Shales &c.

limestone,"burdiehouse"or"camps"
Sandstones & Shales.

OIL SHALE.
GROUP

OH STtales Fu.mpherston''

Sandstone Hajles "

War die Shxiles.

Sandstone Crai^Teilh' & Granton"

Andesiies
.S as alts

T Sandstones, Shales & Limestone

Masidt ;

7 Tarieaated C lav s , Maris ,

Shales & Sandstones tviih hands
&Kod2iles of Cements toTie and

-i Cornstones near liase.

Calcareous Sajidstones Crai^milLar

Fig. 17. Diagram showing relation of strata and their probable
thickness in the Carboniferous Formation round Edinburgh. De-
tailed prominence is given to the lower or freshwater Calciferous
beds with their oil shales and related strata. These are often rich
in fish remains. (From Traquair).

ARTHURS SEAT
VOLCANIC GROUP

CEMENTSTONE
GROUP

"ballagan" beds

In Carboniferous and Permian Epochs 143

the Lower Limestone as in considerable part marine, the
Edge coal as freshwater, the Upper Limestone as in part
freshwater, in part marine, the Coal Measures as almost
wholly freshwater. But in order to discuss this question
more intelligently, there is appended the lisf given by
Traquair of the entire fish-fauna of the Edinburgh rocks.

From the subjoined list (p.p. 144-45) it will be seen that
while elasmobranchs are most largely confined to the "Low-
er" or "Upper" Limestone, that are accepted as marine,
Acanthodes sidcatus is common to the freshwater Burdie-
house and Dunnet shale ; Tristychius arcuatus is reported
from the Burdiehouse and Wardie shales, but also from the
Upper Limestone; several occur in the Edge Coal and
Upper Limestone; Sphenacanthiis serriilatus and Cyno-
podius crenulatus in the freshwater Burdiehouse, Dunnet,
and Edge Coal deposits, but also in the marine Upper
Limestone.

But more remarkable is the list of crossopterygian and
accipenseroid forms, for Rhizodus hibberti — a most typical
freshwater species is also recorded from the Lower and
Upper Limestone. The same is true of Elonichthys robi-
soni, Nematoptychius greenocki and Eurynotus crenatus,
all common and typical freshwater fishes of the Edinburgh
Calciferous rocks, But it should most importantly be ob-
served here that all of the above species come either from
the "Gilmerton Ironstone" beds of the Lower Limestone
Series, or from the "South Parrot Coal shale" of the Upper
Limestone Series, both of which are freshwater beds inter-
calcated amid what are mainly true marine limestones.
Traquair however gives a list of what had now become
either anadromous or wholly marine fishes (op. cit. p.
693) as follows:

Cladodus mirabilis Copodus planus

Cladodus striatus Psammodus rugosus

Petalodus acuminatus Cochliodus contortus

Ctenoptychius lobatus Xystrodus striatus

Ctenoptychius serratiis Poecilodus jonesii

Petalorhynchus psittacinus Psephodus magnus

Polyrhizodus magnus Acondylacanthus jenkinsoni

Pristodus falcatus Harpacanthus fimbriatus.

144 Evolution and Distribution of Fishes

LIST OF FISHES, EDINBURGH DISTRICT

Elasmobranchii

Pleuracanthus laevissimus

Pleuracanthus elegans

Pleuracanthus gracillimus ,
Pleuracanthus horridulus . ,
Pleuracanthus fastigiatus .

Diplodus gibbosus

Diplodus parvulus

Cladodus mirabilis ,

Cladodus striatus

Dicentrodus bicuspidatus . ,
Janassa linguaeformis . . . . ,
Petalorhynchus psittacinus .
Petalodus acuminatus ....
Ctenoptychius serratus ....
Ctenoptychius lobatus ....
Ctenoptychius apicalis . . . . ,

Polyrhizodus magnus

Callopristodus pectinatus .

Pristodus falcatus

Copodus planus

Psammodus rugosus

Helodus simplof

Pleuroplax Rankinei

Pleuroplax falcatus

Xystrodus striatus

Cochliodus contortus

Poecilodus Jonesii

Psephodus magnus

Acondylacanthus Jenkinsoni

Lepracanthus Colei

Tristychius arcuatus

Tristj'chius minor

Euphyacanthus semistriatus
Sphenacanthus serrulatus .
Sphenacanthus hybodoides

Gyracanthus rectus

Gyracanthus nobilis

Gyracanthus youngi

Gyracanthus formosus ....
Aganacanthus striatulus . . .
Cynopodius crenulatus . . .

Euctenius elegans

Harpacanthus fimbriatus ..

Harpacanthus major

Acanthodes Wardii

Acanthodes sulcatus

Acanthodopsis Wardii ....

T3 0)

•a «
= E

Cw

O (U

0..5

In Carboniferous and Permian Epochs 145

LIST OF fishes, EDINBURGH DISTRICT— Continued

4)

II

c

to

J=

0, u

Ea
3 J=

3

£i
4)

li

0)

B

'A

u

•a
U

a>
c

3

Crossopterygii

Megalichthys Hibberti

Megalichthys laticeps

Megalichthys laevis

Megalichthys pygmaeus ....

Megalichthys sp

Rhizodopsis sauroides

Rhizodus Hibberti

*

*

*
*

*

*
*

*

*

*
*

*

#

*
«

Rhizodus ornatus

Strepsodus sauroides

Strepsodus sulcatus

Strepsodus striatulus

Coeiacanthus elegans

Coelacanthus abdenensis . . .

*
*

*

Dipnoi
Uronemus splendens

*

*
?

*

*

*

*

*
*

*

Ctenodus interruptus

Ctenodus cristatus

*

Ctenodus angustulus

Sagenodus quinquecostatus . .

Acipenseroidei

Eurylepis scoticus

Gonatodus punctatus

Gonatodus inacrolepis

Gonatodus parvidens

Drydenius insignis

*

*
*

*
*
*
«

*

*

*

*
*

*
*

*
*

*

*

*

*
*
*

*
*
*

*

*

*
*
*

»

♦

*

*
*
«

*

*

*
*
*
*

*

*

*

?

*
»

Elonichthys Robisoni

Elonichthys striatus

Elonichthys pectinatus

Elonichthys multistriatus . . .

Eloaichthys Aitkeni

Mesopoma macrocephalum...
Acrolepis semigranulosa . . .
Rhadinichthys ornatissimus .
Rhadinichthys carinatus . . .

Rhadinichthys brevis

Rhadinichthys ferox

Nematoptychius greenocki . .

Cryphiolepis striatus

Eurynotus crenatus

Eurynotus macrolepidotus . .

Wardichthys cyclosoma

Cheirodus granulosus

Cheirodus crassus

*

146 Evolution and Distribution of Fishes

As the author then well remarks: "not one of the above-
quoted species occurs in any of the lists which I have given
from the Calciferous Sandstone Series of the district, while
all of them except Harpacanthns fimbriatus are well known
from the Mountain Limestone of England, and except
Pristodus falcatus, of Ireland likewise." It will be noted
also that the above list consists wholly of elasmobranchs.
From abundant evidence advanced by several of the British
palaeontologists however, it is evident that a few of the
hitherto inland fishes, and also these elasmobranchs were be-
coming anadromous, or even had become wholly littoral
marine species. Previous papers by Traquair (9^: 1:34;
g^: 2:540) as well as subsequent ones support a like con-
clusion.

A richly fossiliferous set of Scottish Calciferous rocks
is met with in the Eskdale-Liddesdale region. Peach,
Kidston, and Traquair have jointly studied its organisms.
Freshwater crustaceans, eurypterids, and scorpions, as well
as 28 species of fish were listed. Kidston, in discussing the
fossil plants, joins hands with Peach in emphasizing the
striking similarity of the organisms they studied, to a set
from Illinois studied by Meek and Worthen.

But that fishes were by no means the most highly evolv-
ed animals of the Calciferous age is proved by Huxley's
description of the Amphibian Pholiderpeton from the Forth
basin, while the other genera described by him from Ireland,
give proof that during the Old Red period, certain derivative
descendants from some group of the fishes, had already
become by degrees evolved and modified up to the amphi-
bian stage. The writer has already claimed that the direct
line of ascent is to be sought for in types allied to the
cyclostomes; from these intermediate organisms probably
led to primitive representatives of the Amphibia apoda,
thence to simpler, and later to more evolved, Urodela.
The writer fully realized, when the claim was made, that
very slight palaeontological evidence existed in favor of
such a view. But the serious gap has been considerably
bridged over since, and this most perfectly by recent publi-
cations of the Carnegie Institution. Most suggestive is

In Carboniferous and Permian Epochs 147

Moodie's memoir on "The Coal-Measure Amphibia of
North America" (95). The genera Molgoph'is, Cocytinus,
Ptyonius, Aestocephalus and Lysorophiis, seem to be at
least some of the desired types. But further investigation
of Old Red and of Calciferous as well as more recent rocks,
for the discovery of advancing organisms between cyclo-
stomes and aistopod batrachians, is greatly needed.

In eastern North America, the Calciferous or Culm
of Europe seems synchronous with the extensive — though
often marine — beds that make up the Mississippian series.
The marine beds yield a varied and very typical marine
fauna, the invertebrate fossils of which have been copiously
listed, though fish remains are rare or conspicuously absent.
But the Mauch Chunk of Pennsylvania and West Virginia;
the Waverley and Cuyahoga shales of Ohio; the Mauch
Chunk and Pennington of Virginia; the Burlington of
North Missouri and Illinois; also the Horton of East
Canada, give ample evidence of a combined freshwater and
land flora and fauna. These also are even more varied and
extensive than those of the Old World. They have been
described mainly by Hall, Dawson, Newberry, Worthen,
Whiteaves, Eastman, Lambe, and Condit amongst others.

The earlier and succeeding editions of Dawson's
"Acadia" opened up wide palaeontological vistas. In de-
scribing the Horton series of Nova Scotia (55:251) and
the Lower Carboniferous or Albert shales of New Bruns-
wick, Dawson (96:237) and Lambe (gy : i) refer to an
exactly similar biological aggregate as that of Europe.
Swarms of phyllopod and other entomostracans such as
Leaia leidyi, Estheria sp. Leperditia siiberecta^ eurypterids,
scorpions, millipedes and insects — mainly orthopterous, —
freshwater molluscs, great shoals of fossilized fishes, "and
footprints of batrachians" occur, but no strictly marine
remains.

Speaking of a thin bed (No. 6 of Division 4) "full of
remains of small fishes" Dawson says: "It has a true stig-
marian underclay. I suppose it to have been a swamp or
forest submerged and occupied by fishes, while its vegeta-
tion was still standing. It contains remains of fishes of the

148 Evolution and Distribution of Fishes

genera Ctenoptychius, Diplodus, Rhizodus and Palaeon-
iscus. It also contains Cythere^ Naiadites {Anthracomya)
and Spir-orbis. In the other beds which contain fish remains,
most of these consist of small lepidoganoids, but there are
occasional teeth and scales of large species of Rhizodus,"
and also teeth of elasmobranch fishes of considerable size,
some of which he describes and figures. Later he adds:
"the larger ganoids, and the shark-like Diplodonts no
doubt preyed upon the smaller fishes, as the abundant
scales seen in their coprolites prove. The flat-toothed
sharks like Psammodus and Conchodiis may have ground
up the shells of Naiadites."

Both authors, in describing the freshwater Albert
shales, were equally arrested by the conditions that sur-
rounded and in part caused wholesale destruction of, the
fishes. Thus in describing the five species of Rhadinichthys
[Palaeoniscus of Dawson) Dawson says (9(5:340) : "The
whole of these fishes have been preserved entire, the body
being perfectly flattened, and thrown into attitudes which
Imply that they were embedded when living, or immediately
after death. The material in which they are contained is
shown by its microscopical and chemical characters to have
been a vegetable muck or mud, and the fish were entirely
overwhelmed by it, in the manner of a bursting bog, or
were stiffled by the non-oxygenated water mixed with this
mud, and suddenly killed and embedded in the accumulating
sediment." Here, as in the frequent preservation of fish
and other organisms in the fossil state, sudden flood-plain
freshets might explain the results, though the sudden throw-
ing into the water of deleterious products seems more
likely

Lambe draws an exact parallel between the Albert
beds and those of the Scottish Calciferous system. But
regarding the fishes he says: "they belong to the same
genera, but differ as to species." This, however clearly
indicates that some important and continuous land-connec-
tion united both areas, as the chart of Freeh sets forth.

A noteworthy feature of these Albert shales is their
apparent Identity In color, consistence, and oil-content with
the oil-shales of the Scottish Calciferous system. Thus they

In Carboniferous and Permian Epochs 149

are of a dark grey to brown color, are of a fine close grain,
they split into layers or sheets, and the strata are 5 to 6
feet thick. But the bands form only a thin part of the
shales arid sandstolnes in which they He. These have
been grouped as follows by Lambe (p. 11) :

Calcareo-bituminous shales, from grey to dark brown in color,

including the so-called Albert shales 850 feet

Grey bituminous and micaceous oil-bearing sandstone, and lower
conglomerates, in massive beds, usually of reddist tint, and
unconformable to the preceding 700 feet

Following R. D. Stewart he inclined to view the bitumin-
ous material largely as a product of plant decomposition.
He also regarded the fishes as being marine, for he ob-
serves: "It is probable that the waters in which lived the
fishes about to be described, were cut off to a great extent
from the sea, and formed the lagoons in which the material
that produced the shales was deposited." And as to the
quantity of these fishes he adds: "the numberless remains of
fishes In some of the beds can be attributed only to the
occasional wholesale destruction of the fishes." But the
associated plants, the correlated resemblance in details to
the Scottish beds, the complete absence of true marine
remains, and the undoubted freshwater habitat in other
regions of the genera he treats of, clearly prove the beds
to be freshwater deposits. In this, as in many other cases
now cited, we would trace the origin of the bituminous
supplies to chemical or biochemical decomposition of the
oils contained in the fishes.

Of the fishes that he describes he remarks regarding
Rhadinichthys alberti that It" evidently swarmed In count-
less numbers In the waters of its time." Scarcely less
abundant was Elonichthys browni, the general aspect of
which, as well as the structure of the ganoid scales from
different parts of the body are shown In Fig. i8.

In the eastern and central States, conditions closely
simulating those already given, prevailed during deposition
of the middle and upper Misslsslppian. But such often
alternated with invasions of the sea, and so of a marine
fauna. This is well set forth In the elaborate reports of

150 Evolution and Distribution of Fishes

-.- >v - ' ' ''"

3 . -

Fig. 18. Elonichthys bro-zcni. — i ; outline restoration of fish,
one-half natural size; 2, 3, two t3pes of flank scales; 4, ridge scale;
all enlarged: 5, portion of dorsal fin-rays and marginal fulcra; 6,
portion of rays from base of dorsal fin. (All reduced from Lambe).

the Pennsylvania, New York, Ohio, Illinois, Iowa and
other State Surveys. In several of these also, bone or
"fish-beds," that vary from one to several inches in thick-
ness occur. Lesley frequently refers to these in Pennsyl-
vania. But the most noteworthy probably are four thin and
apparently marine beds that have been studied by Newberry
and Worthen in the Burlington zone of Illinois {g8 : 12).
One of these, in which the teeth and spines of fishes are em-
bedded in great numbers "stretches at least from Quincy,
Illinois ... to Augusta in Iowa," points nearly a
hundred miles apart. This indicates that the cause which
produced such general destruction amongst the vertebrated
animals of this period was not local, but operated simultane-
ously over a wide geographical area.

To the writer it seems that such an area, at least 10,000
square miles in extent, and continuously covered with the
remains of fishes that were however of freshwater
ancestry, supplies the best possible explanation for origin
of the Illinois oil beds. The soft perishable oily parts

In Carboniferous and Permian Epochs 151

seem to have supplied the oil, the hard parts to have sup-
phed the contents of the probably true marine elasmobranch
"bone-beds."

A detailed study of the numerous published lists of rock
sections given in the State surveys, or in some of the geo-
logical magazines, reveals how very unstable was the earth's
crust up to this time, and how frequently alternation of
freshwater and of marine conditions prevailed. The
natural outcome is that the geologist, who accurately takes
note of each horizon and of its fossil contents, constantly
records from adjoining and often thin beds, a freshwater
and then a marine list of organisms. An excellent example
of this is furnished by Condits "Conemau.gh Formation
in Ohio" (p9), which though dealing with the Higher
Carboniferous beds, is typical for those now treated of.

As demonstrating also the widespread destruction to
fish-life that proceeded now, contemporaneously with the
evolution of new types, we may note in passing that the
unwieldy and giant fishes, like Coccostetis, Phlyctaenaspis,
Dinichthys, Titanichthys and Macropetalichthys, typical of
the North American Upper Old Red period, had wholly
died out by the close of the Mississippian, and had been
replaced by a higher, more lithe, and more voracious type
of fish, belonging to freshwater elasmobranch, and, to a
lesser extent, to crossopterygian affinities.

The Mountain Limestone and Millstone Grit. Between
the Lower and Uppermost Carboniferous formations of
Europe, there are often intercalated two extensive sets of
rocks that in Britain have received the above designation.
The former is very largely of marine origin, though at
times showing intercalated freshwater beds. It may be
as much as 4,000 feet in thickness. The latter is singularly
devoid of organic remains, but varies from 1200 to 5500
feet in thickness. As the writer abundantly verified about
forty years ago, and as the published results of Kidston for
plants, and of Peach and Traquair for animals has equally
demonstrated since, the "Grit" beds separate two totally
distinct biological groups of organisms, that are specifical-
ly and often even generically or ordinally distinct. These
are the Lower Carboniferous, Culm or Mississippian, and

152 Evolution and Distribution of Fishes

the Upper Carboniferous, True Coal Measures, or Penn-
sylvanian.

Probably no other formation has been so fully and
readily accepted as of freshwater or terrestrial formation
than the latter, for it and the important coal-beds of the
world have been inseparably linked in human thought for
the past fifteen decades. So while we would view the
petroleum oils of the Old Red and the Lower Carbonifer-
ous formations as being fish derivatives, it is equally true
that the pure carbon or coal of the present group is of
vegetable origin. But from its intimate relation to an
abundant fish-life, it is not at all improbable that some types
of coal, like the cannel or parrot, largely owe their bitumin-
ous properties to intrinsic permeations of fish oil.*

But before treating of the biological assemblage that
characterizes the Coal Measures, it should be observed that
the invasion of marine regions by elasmobranch fishes main-
ly, which started in the Calciferous period or possibly
earlier, became a most pronounced event during deposition
of the Mountain Limestone, and was continued into the
Coal Measures. This migrational change is fully discussed
in Chapter 9 (pp. 275-79) ^^^ so consideration of the fish-
groups involved can be deferred meanwhile.

The Coal Measures {or Pennsylvania beds.) The high
economic value of the rocks composing this division has
caused detailed study of its physical and biological features
alike. But it should be borne in mind that though the great
mass of strata composing it suggests a freshwater and land •
origin, continued though less prolonged oscillation of the
earth's crust than in preceding epochs, often caused tempo-
rary marine invasion, over large areas that fundamentally
remained as land masses. Probably the most careful and
extensive demonstrations of this are brought forward by
Kirkby in his paper "On the Occurrence of marine fossils
in the Coal Measures of Fife" (700:378); also by J.
Ward (707:42), and by J. T. Stobbs (702:495). The
last named points out how easy it is to confound fossils

* This subject is fully considered in the writer's volume entitled "Fishes the Source
of Petroleum"' (1923).

In Carboniferous and Permian Epochs 153

of different strata, unless the observer has himself dug out
the fossils and noted the exact locations and relations. He
tabulates eleven distinct marine bands. And in regard
to these, as compared with the greatly more extensive and
thick terrestrial bands, Hind in a palaeontolo^ical Supple-
ment says that there are two distinct molluscan faunas,
which recur with irregular alternations. The freshwater
fauna is characterized by the Unio-like genera Carhonicola
and Anthracomya, and the Dreissensia-like Naiadites; the
other by Pterinopecten papyraceus, Possidonella, with many
species of cephalopods, and the two never mix.

But on the succeeding page he states, for "the marine
band associated with the Gin-mine Coal" that the two
elasmobranch genera Listracanthus and Edestiis occur in
it. Quoting other localities for Listracanthus he reaches the
conclusion that "Listracanthus is associated with a marine
fauna. We may therefore consider that Listracanthus
always had a marine habitat. Many of the fishes associated
with it in the bed below the Gin-mine are also found with
a non-marine fauna," and he appends a list setting this
forth. Bolton (70^:424) and Woodward (70^:486) also
record Listracanthus in nodules of shale strata, and con-
clude that these are all marine beds. So it evidently is an
elasmobranch which had largely left a freshwater habitat
and mainly lived in marine surroundings. This is discussed
later (p. 275). But here it may be said that all of the
other fishes listed by Hind (p. 529), and including Edestus,
were freshwater.

The environal relations of Coal-measure organisms
have been so often described, and more or less correctly
figured, that a general word-picture is unnecessary. Nor,
in view of the surprising similarity of the rocks, of the
factors which gave rise to these, and of the organisms
enclosed, need we deal with localized areas, in their physical
or biological relation to fishes. Rather it might at once
be stated — in view of the knowledge we now have of Coal
Measure strata and their fossils — that some such compact
and yet extensive connecting land areas, as are traced by
Freeh (705:83) are a necessity for the understanding
of the facts and problems involved.

154 Evolution and Distribution of Fishes

Extensive lists of the plants have been given in the
past half-century by Lesquereux, Dawson, Lester Ward and
Fontaine in this country; by Lindley and Hutton, William-
son, Kidston, Seward and others in Britain; by Zeiller,
Renault and Grand d.Eury in France; and by Weiss, Feist-
mantel, Stur, Barrois and others for Germany-Austria.
All agree that wide land areas of low flat swampy character;
of warm but moist humid atmosphere, during some seasons
of the year, alternating with hot, bright — almost xerophy-
tic — conditions at other seasons; were typical. The far-
reaching but comparatively shallow waters of lakes, slug-
gish rivers and lagoons teemed with such phyllopods as
Estheria tenella, Leaia leidyi and a variety of freshwater
ostracods. These seem to have formed the food for great
shoals of freshwater fishes of rather sluggish habit, as did
also the gasteropods and the abundant pelecypods like
Carbonicola, Anthracomya, and Naiadites {io6), all or
most of which hung by byssus threads from the trunks of
the swamp-loving trees, as Dawson and Hind have shown.
Alongside these were great eurypterids, whose specific de-
tails have been elucidated by H. Woodward (loy), Laurie
(70<§': 151, 509) and Glarke-Ruedemann {6^). The last
however were fast disappearing, compared with their more
giant predecessors of the Lower Carboniferous, Old Red,
and Silurian ages. Scorpions, spiders, and insects were
abundant, while in the swamps, flood-plain pools, rivers
and lakes, a new and diversified fish fauna existed. Before
dealing with this in some detail, it might be stated that a
rich amphibian evolution had resulted in the appearance of
types varying from 2 or 3 inches long to others that were
6 to 8 feet. Many of the latter, like their coccostean and
other piscine predecessors were heavily armored and clumsy
animals. So, if the abundant vegetation of the period
caused it to be called "the age of plants," equally truly
might it be called "the age of amphibians." The older
records by Dawson, Huxley, and Miall as well as the recent
publications of the Carnegie Institution (lOg) by Case and
Moodie fully demonstrate this.

Viewed as a whole the fish fauna of the period was
surprisingly uniform in general types, but differed in the

In Carboniferous and Permian Epochs 155

distinctness of the species or at times of the genera. So
whether we compare lists gathered across the world from
the Eastern States to Australia, or from Canada to Cape
Colony the general resemblance is striking. Further this
fauna was to a large degree freshwater, the elasmobranchs
alone being the group that still sent voracious and predatory
outliers into the seas of the period. The number and affini-
ties of these are set forth in Chapter 9 (pp. 279-80).

Even the primitive sharks like Cladodiis, Chomatodus,
Diplodus, PleiirodiiSj and Ctenoptychius were still lake-
dwellers, or were anadromous in some species, or fresh-
water in some and anadromous in other species of a genus.
The remains of many of these therefore belonged to the
groups Ichthyotomi, Petalodontidae, and Psammodontidae,
which were loosely cartilaginous, but can be recognized in
their hard teeth and plates, which are often intermingled
beside freshwater chondrosteans, dipnoans, and crossoptery-
gians.

J. W. Davis gives {iio: S^) a graphic picture, derived
from study of the Cannel Coal of Yorkshire. This forma-
tion, as he states, was due to decay of abundant vegetation
that became "aggregated in a small inland lake, very
shallow and liable to be dried up. The plants forming the
coal were washed into this lake by streams, and becoming
decomposed, and settling to the bottom, accumulated in
a homogeneous mass, prior to its being changed by pressure
and chemical causes into coal. The interlamination of
shales, more frequent and thicker near the sides of the lake,
would naturally result from the mud, also brought down by
the streams, settling to the bottom more quickly than the
leaves of the plants, but at the same time carrying down
with it a large percentage of carbonaceous substance. In
some parts the lake appears to have become filled up or
elevated above the water-level; and seat-earth filled with
Stigmaria rootlets was the result. From the seat-earth
grew plants whose remains *have formed thin bands of
ordinary coal.

"After the accumulation of the decaying vegetable
matter, sometimes deposited in water and forming cannel

156 Evolution and Distribution of Fishes

or gas coal, at others on land, and resulting in thin beds of
ordinary coal, the whole was submerged beneath the water,
and an average of from 1-2 feet of black bituminous mud,
containing few traces of animal exuviae, except an occa-
sional layer of Entomostraca, was deposited. Above the
black shale there is a light-grey colored stratum, about
10 in. to I ft. thick, which is almost, or entirely composed
of the shells of Anthracosiae. Countless numbers of the
shells of these molluscs occur; they are always found
crushed. They were the shells of animals such as would
be found at the present time inhabiting and luxuriating
in semistagnant pools. . . . Above the shell-bed are
about twenty feet of bluish-white shales, containing several
layers of ironstone nodules. Shells of Anthracosia are
common in the ironstone, but do not occur in the shale.
All of these facts point to one issue — that we have in these
beds an example of an inland lake of freshwater origin.
This is a most important conclusion when we come to con-
sider the variety of fish-remains which have been obtained
from these strata.

"The fossil fish are found in greatest abundance at Ting-
ley; where the coal has been worked, elsewhere fish remains
are either quite absent or occur with great rarity. At
Tingley they are found in largest numbers between the
cannel coal and "Hubb," many beautiful examples how-
ever have been obtained from all parts of the cannel coal,
and they not unfrequently occur in the 'Hubb.' The follow-
ing is a list of the fishes which I have been able to identify:

Coelacanthus lepturus
Ctenodiis elegans
Megalichthys Hibberti
Rhizodopsis sp.
Palaeonisciis sp.
Gyracanthus formosus
Ctenacanthus hybodoides
Diplodus gibbosus
Ctenoptychius pectinatus
Helodtis simplex
Ostracanthus dilatatus
Compsacanthus triangularis
Compsacanthtis major
Cladodus teeth
Petalodus

R/iizodus — scales
Ctenodiis sp. ribs and bones
Pleuracantlnts laevissimtis
Pleuracanthns erectus
Pleuracanthus pulchellus
Pleuracanthns alternidentatus
Pleuracanthus alatus
Pleuracanthus robustus
Pleuracanthus (Orthacanthus)

cylindricus
Spirorbis carbonarius
Entomostraca
Julus f

Anthracosia (Unto)
Labyrinthodont (?) ribs, teeth, etc.

In Carboniferous and Permian Epochs 157

He then adds "Most of the fishes composed in this
list belong to the Elasmobranchii and Ganoidei; but where-
as the Elasmobranchii are generally considered to be of
marine origin, and the ganoids rather to pertain to fresh-
water, we have them both in this case, fossil together, and
evidently deposited in the immediate neighborhood of the
spot where they lived. The sharks were of large size."
He then refers to the relative abundance of each lot of the
above, and later compares his own results with those of
Newberry (^5:284) and proceeds "after careful study
of the deposit Dr. Newberry considers that there was in
this locality at the time when the coal was forming, an open
lagoon, densely populated with fishes aiid salamanders,
and that after a time this lagoon was choked up with grow-
ing vegetation, and peat (which afterwards changed to
cubical coal) succeeded to the carbonaceous mud (now
Cannel) that had previously accumulated at the bottom
of the water." He then states that Newberry found nine
species of Eurylepis, a small tile-scaled ganoid, two or three
species of Coelacanthiis (closely allied to C. lepttirus of
the English Coal Measures), scales and teeth of Rhizodus,
spines of Orthacanthus and Compsacanthiis^ and teeth of
Diplodus. The striking parallelism as above revealed Is
arresting.

Two extensive and specially suggestive British papers,
alike from the physical and biological standpoints are: (i)
"List of Fossil Fishes" in the "Catalogue of Western Scot-
tish Fossils" by Professor J. Young, and (2) "The
geological Features of the North Staffordshire Coal Field"
by John Ward. In the former a most extensive list is given
of all known western fossil fishes found in the Carbonifer-
ous Lime or in the Coal Measures. Reference to p. 279
will show that of Elasmobranchii thirty species are either
freshwater or are anadromous, and thirty-three species are
now marine, these too are almost wholly from the Lime-
stone series. But of "Ganoids" and dipnoans, thirty-two
species, or all recorded, are from freshwater beds. Many
of the last also, as well as of the freshwater ganoids, oc-
curred In beds that yielded remains of six species of Laby-

158 Evolution and Distribution of Fishes

rlnthodont belonging to as many genera. These, like other
amphibians, were intolerant of saltwater.

Ward's paper confirms and even extends the results
of Young.

Papers that treat of the Northern and North-east
French coal-fields, of the Belgian and of the east German
fields, largely duplicate the conditions above revealed.

The total thickness of the Coal Measures in Britain
has, by Hull, Geikie, Ward and others been estimated at
2,000 to as much as 12,000 feet, though 3,000-5,000
includes average variations.

Over the eastern half of the North American conti-
nent the Coal Measures cover several widely extended
regions in all of which rich coal beds occur. That a nearly
or quite synchronous connection existed between these and
the above Measures of the Old World is assured from
many considerations, and not least from the generic or
even specific identity of the organic remains. The occas-
ional variability in species or genera probably favors the
view of Chamberlin, that definite and isolated centres of
physical as well as organismal formation existed. Thus
while the Michigan and Rhode Island areas may each have
remained distinct for a protracted period, continuity prob-
ably was kept up in the Pennsylvania, Ohio, Kentucky and
Tennessee regions. Again the Illinois-Indiana region may
have had at least slight connection with the Missouri-Iowa
area, and so on. But until very exact stratigraphic and
palaeontological evidence is at hand, we can only approxi-
mately surmise.

Equally as suggesting the possible mode of origin of
coal, the great stretches that must long have remained as
swampy lakes, and the types of associated organisms in these
lakes, Newberry's account of the locality above referred to
may be quoted from a later publication (86). "The Linton
(Ohio) locality is especially interesting and instructive.
It has already yielded more than twenty species of fishes
and nearly forty species of aquatic amphibians, all inhabi-
tants of the same body of water. These are found in a
thin stratum of cannel, which, over a limited area, underlies

In Carboniferous and Permian Epochs 159

a thick bed of cubical coal, of which the place is near
the top of the Lower Coal Measures. This is a bed of
coal which extends over some thousands of square miles,
and it is usually a soft coking coal, not unlike that of the
Pittsburg seam, which lies about 500 feet higher. At
Linton, however, we have evidence that the great marsh
in which the peat accumulated that formed Coal No. 6
was for a time a lake or lagoon, inhabited by the fishes or
amphibians to which I have referred. While this remained
an open body of water carbonaceous mud accumulated at
its bottom, cierived from the drainage of the neighboring
marsh, which carried with it fine particles of completely
macerated vegetable tissue. In this carbonaceous mud that
is now cannel coal, were buried the scales, bones, spines,
and often entire individuals of the inhabitants of the waters
above. Sometimes nearly the whole mass is made up of
animal debris. Many of the fishes and amphibians were
highly carnivorous and powerful, as we learn from their
teeth and coprolites."

Chamberlin describes life in the North American coal
areas (5:11:6x3) as follows: "Aside from the develop-
ments of the freshwater fish and of the amphibians, which
have already been sufficiently emphasized, perhaps the most
suggestive feature was the association of the arthropods
with other forms of life. Eurypterids were still in exist-
ence, and their relics are so intimately associated with
beautifully preserved ferns, calamites, insects, spiders and
scorpions, as to leave no reasonable doubt that they were
freshwater forms. In the more notable localities, as at
Mazon Creek, Illinois, and Cannelton, Pennsylvania, the
fern fronds were preserved with almost perfect fidelity and
without the coiling, crumpling and shredding that would
have inevitably attended transportation for any notable
distance. At the famous locality on Mazon Creek, un-
crumpled fronds form the centers of thousands of con-
cretions, and insects, spiders, scorpions and eurpyterids
form the centers of others associated with them. All must
have been fossilized with a minimum of transportation,
and under the most quiet conditions. Almost equally in-

i6o Evolution and Distribution of Fishes

structlve is the association at Cannelton, though the vege-
tation is more fragmentary."

The rich eastern Australian oil shales that have been
described by Carne {112) and others, also the associated
beds of calcareous and arenaceous shale, have yielded as
yet few traces of fishes. Suessmilch, however, notes (US'-
138) that: "a fossil fish (Urosthenes aiistralis) has been
obtained from the Upper Coal Measures, both in the
Lithgow and Newcastle districts, while from the latter
locality the wings of some undescribed insects, belonging
probably to the Neuroptera, have been obtained." A
labyrinthodont and abundant fossilized plants alongside
caused him to regard all as of freshwater origin.

The remarkable set of fish remains that has been de-
scribed by A. S. Woodward {114:1) from calcareous,
arenaceous, and shale beds of Mansfield in Victoria, prob-
ably belong to the same rock series as that which fur-
nished Urosthenes further north. They indicate a Car-
boniferous age, and are preserved alongside abundant plant
remains in some strata, though without trace of marine
organisms. The most striking and probably most abundant
type of fish is that named Gyracanthides murrayi by Wood-
ward (Fig. 19). Belonging to the primitive elasmo-
branchs, it first clearly revealed the exact disposition of
the formidable fin-spines that have been named Gyr acanthus,
and which occur at times in considerable amount in Car-
boniferous and Carbo-Permian beds from central North
America to Britain. In addition to remains of acan-
thodian elasmobranchs, the other fishes belong to Ctenodus,
a genus of ancient Dipnoans; and to Elonichthys and Strep-
sodtis among ganoids. All of this is added proof that
from northern Europe and America to Southern Australia,
freshwater passageways existed that permitted steady mi-
gration and variation amongst related groups of fishes.

We may shortly sum up now, for the fishes of the Coal
Measures, by saying that the once prevalent and primitive
Ostracoderms and Arthrodires had wholly disappeared;
the primitive and rapidly evolving Elasmobranchs were the
most predaceous and lithe. So some of the latter gradually

In Carboniferous and Permian Epochs i6i

^j

Fig. 19. Gyracanthides murrayi. An ancient but highly modi-
fied Elasmobranch, one-third nat. size. Ventral view of head and
abdomen, but tail twisted to give side view. (Reduced from A. S.
Woodward).

1 62 Evolution and Distribution of Fishes

invaded the sea from early or Mid-Calciferous time on-
ward, while many still kept to inland waters. Of Crossop-
terygians, Rhizodus — in spite of formidable teeth — had
almost died out, but its allies Strepsodus and Rhizodopsis
were abundant in Europe, though rare or largely absent
in America. Coelacanthus, on the other hand, was abun-
dant in both countries. But the Actinopterygii, or "gan-
oids" in the older sense, were, as to number of individuals
and of species, the most abundant. The genus Rhadinich-
thys, that attained its climax in the Calciferous of Britain
and New Brunswick, persisted in several known species,
into the Coal Measures alike of Britain and of the United
States. But the genera Elonichthys, Platysomiis and Acro-
lepis are preeminent in distribution, as they occur from the
Calciferous up to the Permian, and from Bohemia on the
east to Illinois on the west. The last named genus also
seems to have extended from Russia to Cape Colony.

The Physical and Biological Environment of
THE Permian.

In Europe this formation is at times conformable
to and continuous with the Coal Measures, or may be more
or less unconformable. In North America it usually
grades upward so insensibly from the Coal Formation that
the term Permo-Carboniferous (or more accurately Carbo-
Permian as here used) has been widely applied. By gen-
eral consent palaeontologists have viewed it as bringing to
a close the oldest and most primitive of the three great
organic evolutionary stages of stratigraphic history, the
Palaeozoic. But all indications are that during deposition
of its strata, profound changes were proceeding in climatic
conditions; in the relative distribution of land and sea; in
biological stress and strain, or action and reaction amongst
organisms; in destruction of many previously existing
types; and in evolution of new and fast varying types;
in alternation of dry hot xerophytic with cool and even
glacial atmospheric states, over regions of the earth whose

In Carboniferous and Permian Epochs 163

flora and fauna we have already been studying. A sug-
gestive discussion of some of these problems may be found
in Chamberlin-Salisbury's "Geology" (5:11:640-677).

With increasing firming, but also faulting of the earth's
crust, active volcanic and seismic disturbances gave rise to
huge masses of volcanic rock, that not only added to,
hardened, and deformed the older strata, but in known in-
stances aided powerfully in elevating mountain masses, as
has been shown for the Appalachian and Ouachita ranges
in the United States. But in this process much of the
former relatively flat marshy ground of the Carboniferous
seems to have been elevated and converted into wide pla-
teaux, much resembling those of Thibet, and the "bad
lands" of the West. These then became subject to periods
of desiccation, and alternately of rapid denudation, by ac-
tion of rains descending from the mountains.

As gradually elucidated in Europe during the past
seventy-five years by King (//j), by H. B. Geinitz (//<5),
by Weiss, {iij), by Goeppert {118), and specially by
Fritsch {iig)^ as traced in India by Medlicott and Blan-
ford, also by Oldham (720:191), and in North America
by Fontaine- White {121)] by Prosser {122), by Hussa-
kof and Case {12^), the formation exhibits considerable
diversity of character, "that seems largely dependent on
whether the strata were: (a) deposited in a marine hab-
itat; (b) deposited in rather deep lacustrine areas as shaly,
sandy, or gravelly strata; or (c) formed in estuaries,
swamps, lagoons, alluvial plains, and open or covered
woodlands" (725:207:101). These by no means follow
definite and successive relations, but except for the last —
which is best developed near the top of the system — the
marine and lacustrine are often interbedded. The marine
rocks, usually limestone in nature, attain their greatest de-
velopment from the Alps eastward to North India, and in
the western and south western United States. These con-
tain a rather poor assemblage of typical invertebrate ma-
rine forms, but mixed amongst these are no vertebrate
remains.

164 Evolution and Distribution of Fishes

The second stratigraphic type is greatly the thickest
and most typical, being made up very largely of red sand-
stones and conglomerates, at times interbedded with marls,
shales, and coal beds, more rarely with marine beds
like (a) above. In the fine sandstones, shales, and shaly
coals, plant-remains occur that are mostly a curious com-
bination of palaeozoic and mesozoic types. Thus species
of AsterophyUites, Calamites, Sigillaria, Lepidodendron^
and sphenopterid-neuropterid forms, all surviving from the
luxuriant Carboniferous flora, are mixed with Walchia, Bai-
era, Foltzia, Glossopteris and Callipteris, that foreshadow
mesozoic vegetation.

Mixed often with these — as at Autun in France — may
be crowded layers of phyllopod and other entomostracans,
various higher crustaceans, also, according to Fritsch, a
macrostomid predecessor of the King Crab, which he
named Praelimulus, and which like the eurypterids was
thoroughly freshwater; masses of univalve and of bivalve
shells; scorpions and insects. These undoubtedly must have
been only a few that were more resisting in their outer
tissues, compared with many others of softer structure that
quickly decayed.

But vertebrate life was steadily evolving, for while the
fishes became Impoverished In individuals and species, am-
phibians and even reptiles, became Increasingly abundant
and specialized. Details regarding all of these for Europe
are given by Fritsch (iig) and Gaudry {124), and in
America In the Carnegie Publications already cited.

The sumptuous volumes of Fritsch furnish the most
recent and fullest accounts of European Permian condi-
tions, but these pertain to the upper part of the system
that has been termed the Zechstein in Germany. The
lower beds of the system in that region are treated In detail
In Geinitz's work "Die Dyas." But this Lower Permian
Is characterized, much as in eastern Pennsylvania, by ex-
tensive masses of purple-red rock, and so in Germany Is
often known as the "Rothliegende."

Two Important physical factors seem both to have co-
operated In reducing and often obliterating freshwater and
land life, during deposit of the Rothliegende or Lower Per-

In Carboniferous and Permian Epochs 165

mian, as compared with their luxuriance during the Coal
Measure period, throughout Europe. One was the wide-
spread extrusion of igneous rocks as beds of lava, tuff and
dust, or the injection of volcanic material into the older
stratified rocks as extensive dykes. Such must often have
caused a wholesale destruction of plant and animal life over
many thousands of square miles of country.

Another and remarkable change that seems to have
become more and more pronounced during deposition of
the Lower Permian was the initiation of a well-marked
glacial period. In Europe conglomerate beds occur that
seem only explicable as glacial clay and boulder formations.
But it is in the Southern Hemisphere, from South East
Africa to India and Australia, that the most pronounced
examples of glacial phenomena are testified to by the
rocks. It is not surprising, therefore, that while the lower
part of the Lower Permian (Rothliegende) shows marked
resemblances to the Upper part of the Carboniferous, the
Upper Permian shows transition toward the later or Tri-
assic system.

The uppermost zone of the Permian is the Kupfer-
schiefer (copper-slate) which, equally in Europe and in
Texas, shows one or more clay-beds, that are rich in copper
ore. This is the zone also that is usually richest in fresh-
water or land fossils, and whose contents have been most
fully examined.

The accounts alike of Geinitz and of Fritsch testify
to the presence of an abundant freshwater-land flora and
fauna, while the numerous wide stretches of rocks that
show mud layers with rain-pits or sun-cracks, or of shaly
sandstones with tracks of amphibians and shore ripple-
ridges, suggest that dry hot conditions at one time, no
less than glacial climatic states at another, were typical.
But that the flora was often abundant and varied is proved
by the thick coal beds found in the Lower Permian of
France, East Germany, and West Russia, as well as in
India, Australia and South Africa.

The freshwater and land fauna preserved to us consist
of numerous insects, myriapods, estheriae, and specially

1 66 Evolution and Distribution of Fishes

fishes and amphibians, some of the last being of large size
and unwieldy build.

If now we compare the statements made as to the 7ion-
marine Permian organisms, the lists of fossil fishes given,
the relation of these physically and biologically, the prac-
tical absence of fish records from the marine rocks, and
the affinities of these fishes with preceding and succeeding
fish-faunas, the observations of Geinitz and Fritsch for
Bohemia, and of Case for the Western States and specially
Texas, are fairly typical for other areas. Amongst the
fishes, representatives of the selachian or elasmobranch,
dipnoan, crossopterygian and chondrostean groups are all
known. And of these Case says: "There are no forms
which can be called distinctly marine."

But Fritsch, in speaking of the life-conditions of the
elasmobranchs says: "At the time of the Permian for-
mation, the Xenacanthidae in Bohemia probably lived in
brakish water at the months of rivers, and utilized as food
the palaeoniscids, the acanthodians, and many other ani-
mals, which the rivers brought from the dr>'-lands to the
sea during floods." But as if largely or wholly to contra-
dict or minimize the "brakish water" statement he then
adds: "in company with the Xenacanthidae, we encounter
beside the Palaeoniscidae and Xenacanthidae likewise stego-
cephalids, myriapods, estheriae, and insects, which were
brought down from the dry land." Now in giving "stego-
cephalids" it should be observed that all amphibians are
intolerant of even brakish water, and further the entire
assemblage suggests only lacustrine or fluviatile sur-
roundings.

By what catastrophe the elasmobranch fish-life of the
Carboniferous seas was virtually wiped out, we can as yet
only surmise. But that such actually happened will be
fully set forth in another section (p. 286).

The Carbo-Permian beds of America cover a large area
included in North-West Texas, Oklahoma, New Mexico,
and Kansas. Cummins (725:186) and Gordon {126:21)
recognize three zones; (a) a lowest or Wichita, the deep-
est beds of which are in part marine, in part freshwater,
and decidedly suggest their being top-beds of the Carboni-

In Carboniferous and Permian Epochs 167

ferous system; (2) a Middle or Clear Fork Formation,
in which, as in the Wichita, fossils are abundant; (3) an
uppermost or Double Mountain Formation. The organ-
isms in these have been studied by Cope, White, Case, and
Hussakof.

The second of the above named authors also has re-
corded a varied list of plants such as Cordaites, Neurop^
teris, Odontopteris^ Pecopteris and Sphenophyllum, that
are therefore of Carboniferous affinities. But with them
are Gigantopteris, Callipteris, Gomphostrohus, Taeni-
opteris and JValchia, that as strikingly suggest a Triassic
plant-facies.

Case has built up an admirable mental "Restoration of
the Region and Environment in which the Animals lived"
(725:207:147), that deserves quotation in full. He says:
"Considering only the region in Texas and Oklahoma,
which is typical of all the Red beds, we may restore in
imagination a great flat land stretching away from the
Wichita Mountains and the Arbuckle Hills to the east
and south where it joined the ocean waters. The western
border of the flat we do not know. The normally semi-
arid conditi^on of the land was interrupted by incursions
of the sea, and fluctuations of the climate to more humid
conditions. The aridity never attained a degree which
prevented the growth of some vegetation, or the presence
of pools of water and running streams, but was sufficiently
intense at times to prevent the accumulation of much vege-
table debris in swamps or stagnant lagoons. In the times
of increased humidity, the vegetation increased in quan-
tity, the waters accumulated in large areas, and were over-
shadowed by a heavy growth, and the streams expanded
and spread over their flood-plains, leaving masses of ir-
regularly bedded sandstone and clay. . . . Upon this flat,
largely around the pools and streams, lived the wonderfully
complex amphibian and reptilian life. The waters swarmed
with fish and amphibians, and were constantly invaded by
predaceous reptiles in search of food. And he sums up
by saying: "The fauna was one of estuaries, swamps,
lagoons, alluvial plains and open or covered woodlands."

1 68 Evolution and Distribution of Fishes

Directly connected with our special theme is his state-
ment: "in certain places, such as the patches of light blue
clay, where the remains of small amphibians, sharks, etc.,
are generally abundant, plant remains are also common,"
indicating that the animals were entombed in or near their
natural habitat. A striking feature, that physically con-
nects these beds with corresponding ones of Europe is
brought out in his observation that: "The bluish clay is
copper bearing in many places." The term "Kupfer-
schiefer" would apply equally therefore to Texan as to
central European beds.

The subjoined tabular list that he gives at once indi-
cates the variety of the fish-life, and their relation to the
"Illinois" beds of the "Upper Pennsylvania" or top of the
Carboniferous system.

c a

■jz a,

Selachii

Janassa strigilina

Janassa gurleyana

? Hybodus

Ichthyotomi

Pleuracanthus quadriseriatus

Pleuracanthus gracilis

Dicranodon texensis

Dicranodon platypternus . . .

Ctenacanthus amblyxiphias . .

Anodontacanthus americanus
D'tpneusti

Sagenodus dialophus

Sagenodus fossatus

Sagenodus paucicristatus . . . .

Sagenodus periprion

Sagenodus vinslovi

Ceratodus favosus

Gnathorhiza pusilla

Crossopterygii

Megalichthys nitidus

Megalichthys ciceronis

Actinopterygii

Sphaerolepis arctata

Spermatodus pustulosus

Pyritocephalus sp

Plan^somus palmaris

In Carboniferous and Permian Epochs 169

In a paper by Hussakof — likewise published in the
series of the Carnegie Institution (/2j) — "On the Per-
mian Fishes of North America," but further by statement
and table, that author makes a helpful comparison with
the fis-h-fauna of Bohemia.

a
E

V

Si

CO

America

1
1

America

01

'5
c

«

4)

'0

A cant hod a

Dipneusti

Traquairia

Protacanthodes ....

*
*

Sagenodus

Ceratodus

*

*
*

».

Acanthodes

«

Gnathorhiiza

*

*

Ichthyotomi

Pleuracanthus

(Orthacanthus)
(Xenacanthus)

Diacranodus

Selachii

Hybodus

*
*

»
*

#
*

Crossopterygii
Megalichthys

Actinopterii

Sphaerolepis

Spermatodus

Pyritocephalus ....

Sceletopliorus

Phanerosteon

Amblypterus

Acrolepis

*

*

*
*
*

*

*
*
?

*

Janassa

Ichthyodorulites

Ctenacanthus

*

*
*

Tubulacanthus ....
Brachvacanthus . . .

*

*

Progyrolepis

Platj'somus

*

»

*

Anodontacanthus . .

«

*

Acentrophorus ....

*

Hussakof then says: "while the groups represented in
the two are, with the exception of the Acanthodii, the
same, there is a marked difference in the genera respec-
tively represented, proving the long segregation of the
two stocks from which the Permian faunas of the two
localities are descended. The most remarkable difference
between the faunas is the presence of Acanthodii (three
genera) in Bohemia, and their absence in Texas." So the
closing remark of Case is well illustrated by such dis-
tributional details: "The presence of a great North
Atlantic continent in Carboniferous and earlier times is
accepted as a proved fact by all the writers on the subject,
and need not be defended here." He might quite appropri-
ately have added further: "Connection of it also with a
great North-East European, Indian, and Australian land-
mass is strongly suggested."

1 70 Evolution and Distribution of Fishes

Reviewing shortly the groups of Permian fishes, it
may be said that the elasmobranchs are represented by
six species of Pleuracanthus, three of Acanthodes, two of
Diplodus,, and one of Janassa and Wodnika.

In distribution they extend more or less from Bohemia
to England, Illinois, and southward to Texas. Acanthodes
is the most persistent, for species are traced from the Lower
Old Red up to the Lower Permian; while Pleuracanthus,
Janassa and Diplodus extend up from the Lower Carbon-
iferous. The Dipnoans are known by the genera Concho-
poma and Sagenodus, the latter, which occurred in the Coal
Measures, being scarce in Europe, but showing a rich de-
velopment of species, from Illinois to Texas. According
also to Fritsch our present-day Neoceratodus of Australia
was anticipated already by a species of Ceratodus.

Fig. 20. Amblypterus latus, from Lower Permian beds of Le-
bach, Saarbriicken, Rhenish Prussia. About one-half natural size.
(After Traquair.)

The Crossopterygians were represented by two species
of Megalichthys and one of Coelacanthus, both genera
continued from the Carboniferous. The Chondrosteans
were probably the most abundant in individuals, and con-
sisted of Amblypterus (Fig. 20) and Palaeoniscus (Fig.
21), each with five or six species that extended more or
less across Europe, while Acrolepis, Elonichthys, Platy-
somus (Fig. 45, p. 281), Pygopterus and Thrissolepis are
less abundant.

With the close of the Permian, and therefore of the
great Palaeozoic era, it can correctly be said that primitive
fishes first appeared in freshwaters and very largely per-

In Carboniferous and Permian Epochs 171

Fig. 21. Palaeoniscus macro pomus. From Kupferschiefer beds
in Upper Permian of Ilmenau, Thuringia. One-third natural size.
(From restoration by Traquair.)

sisted there, only some genera of elasmobranchs having
migrated into sea waters and became rather abundant along
coastal regions during Carboniferous time. The latter
seem largely or wholly to have died out in the sea during
Permian days. In habit and habitat the earlier fishes were
mainly clumsy ground-feeders, but during deposition of
Old Red strata, they became more active, aggressive, and
strongly carnivorous. This was most true of the elasmo-
branchs with taper body, lithe movements, and well-devel-
oped teeth. So temporarily they were able to migrate
into the sea and live for a time there against competitive
organisms. The other groups, the Dipneustei, the Cros-
sopterygii, and Chondrostei remained wholly freshwater,
or a very few may rarely have become anadromous in
habit. The type of fish thus evolved was largely adapted
therefore to shallow, and often decidedly putrid water, as
Baldwin Spencer has shown to be true for the existing
Neoceratodus (op. cit. p. 3). As an aid, therefore, to gill
action most of the groups evolved an air-bladder, which,
though now absent as an evident structure in the marine
Elasmobranchii of today, seems feebly indicated, according
to Miklucho-Maclay in some sharks (727:448) as a small
open dorsal diverticulum of the oesophagus. While still
retained in the Dipnoi, Chondrostei, and Crossopterygii, as
well as in most freshwater Teleostei of more recent origin,
it has largely or wholly been absorbed in the existing Elas-
mobranchii and marine Teleostei, since it must have become
a hindrance rather than a help when the latter groups
passed into the restless highly oxygenated waters of the
ocean.

172 Evolution and Distribution of Fishes

CHAPTER VI

The Physical and Biological Environment of Fishes.
(c) During the Triassic-Jurassic Period.

I. The Triassic Formation, like others already stud-
ied, can be fairly sharply divided into freshwater and ma-
rine beds. In Europe, the formation has been grouped
under four divisions : the lowest or Bunter, a higher or
Muschelkalk, a third the Keuper, and a highest or Rhaetlc.
Broadly it may be said that over the above region the lower
part of the Bunter, the lower Keuper or Lettenkohle, the
upper Keuper, and the Rhaetic were of freshwater origin.
The upper Bunter, the Muschelkalk, and occasional beds of
the Keuper were marine. But even in the often thick de-
posits of Muschelkalk rocks, strata are met with, that alike
by their plants and their freshwater animal remains, as by
their entire want of marine organisms, proclaim a temp-
orary elevation of land, and sub-aerial or freshwater de-
posits.

The most exhaustive general treatment is that of Freeh
and collaborators {128). But their somewhat mixed and
diffuse treatment is only slightly helpful in an inquiry like
the present. For an accurate estimate of the varying life-
conditions of the period can only be reached from detailed
study of books or papers of individual authors.

If one peruse the extensive lists of fossils given in
"Lethaea" for strata of the typical Upper Bunter, for the
Muschelkalk generally, and for various beds of the Keu-
per, one at once notes that the lists are wholly made up
of invertebrate and typically marine organisms, while ver-
tebrates are wholly absent. But to this are some exceptions.
Thus Wysogorski (/25: II pt. i : 55-57) gives from the
Lower Muschelkalk of Upper Silesia, a typical marine lot
in the Dadocrinus zone, but also a list of what suggest land
or freshwater animals including eight saurian reptiles, one
labyrinthodont (Capitosatirus) , also teeth, plates and
scraps of such fishes as Saurichthys latifrons, S. lepidosteus,
Colohodus chorzowensis, and C. gogolinensis. These

During Triassic and Jurassic Periods 173

again are stated to be mixed up with Myophoria, Lima,
and Terebratiila. But on p. 62 under Upper Silesian Keu-
per he notes that: "The few organic remains belong to
a freshwater fauna, which consists unitedly of amphibians
(Mastodonsaurus) , saurians {Termatosannis) dipnoans
(Ceratodus) , ganoids {Colohodtis and Saurichthys) ,
freshwater mussels and snails {Anoplophora, Paludina) y
So the former probably was recorded from a thin band of
rock, of freshwater origin deposited during some land
oscillation, between marine beds. This view is entirely in
accord then with the finding of Colohodtis and Saiirichthys
in both lists.

Another, and at first sight puzzling, development is
that of the bone-beds of England, of Mid and North Ger-
many, of North Italy and elsewhere. These occur at the
junction of the Rhaetic with the Keuper below, or in the
Rhaetic, or as in the Wurtemburg bone-beds, at the junc-
tion of the Rhaetic and the Lias. It is not unlikely that
one of these bone-beds at least may represent one continuous
stratum, for in England and over a large part of the Eu-
ropean continent, the Rhaetic bone-bed seems always to
adjoin an extensive marine deposit, whose most abundant
fossil is Aviciila contorta. So it is known as the "Avicula
contorta" zone. In the bone-beds proper occur Ceratodus
latissimus (altus), C. parvus, C. silesiacus, the teeth or
spines of Acrodtis minimus, Hybodus minor and H. laevius-
cidus, as well as bones of reptiles. Either above, or in close
proximity, are beds with abundant plant-remains.

Now all of the above genera of fishes, as well as the
associated organisms, belong to groups that in the palae-
ozoic rocks are clearly freshwater. The probable explana-
tion is that though marine beds may be near to or ad-
joining each bone-bed above or below, the latter was formed
on a land surface owing to some sudden and comparatively
short-lived upheaval of what had been a marine bed. Soon
thereafter and as a nearly concomitant event, terrible and
widespread destruction of freshwater fishes caused strand-
ing of these on top of the upheaved marine beds. These
fishes then underwent decay during deposition of the mud
or micaceous clay that now surrounded them. So their

174

Evolution and Distribution of P^ishes

teeth, bony plates, scales and dental spines were alone left
in countless numbers as main constituents of each bone-bed.

The above view is eminently favored by such a section
as that given in Arthaber's article on the Raibl fish-
deposits. It is here seen that (725:298) the fish-strata
lie between an upper and a lower marine band, the latter
with corals and echinoids, the former with marine molluscs.
The freshwater zone includes typical land plants, also the
fishes Pholidopleiirus typus, Belonorhynchiis striolatus and
Ptycholepis raiblensis.

But another and equally noteworthy feature of the
Trias, that is connected also with the above bone-beds as
we believe, is the occurrence, in midst of marine dolomitic
strata, of deposits rich in fish and reptilian remains, but
characterized further by their highly bituminous and even
asphaltic quality. The bituminous beds at Besano near
Lake Lugano, the Perledo beds near Lake Como, the Lu-
mezzane beds in Lombardy, the Giffoni beds of Salerno,
the Tyrolese beds of Seefeld, and the Raibl beds in Car-
inthia, are all highly bituminous. As noted below also the
Upper Triassic beds of Eastern America are often of like
nature. Deeke, Basano, Kner, Newberry and others have
described the rich fish-fauna that characterizes these beds.
Such genera as Heterolepidotus, Lepidotiis, Semionotiis
(Fig. 22), Pholidophorus, Coelacanthus, Catoptenis, Dicty-
opyge and Belonorhynchiis are typical. All of these genera
were of freshwater habitat.

Fig. 22. Semionotus {Ischyptenis) agassizii. A Triassic fish
common to the rocks of New Jersey and New England. About
one-third natural size. (Reduced from Eastman).

During Triassic and Jurassic Periods 175

Now we would not only claim a freshwater origin for
these fishes, we would further suggest that the bituminous
material is a direct product of decomposition of oily con-
stituents set free from the decaying fish. The statements
quoted below from Newberry leave little doubt regarding
this, while the statistics already presented furnish proof
that wholesale destruction of a teeming freshwater fish-
life was the source for, and furnished the supplies of, the
Triassic bituminous material.

In spite therefore of the apparent mixing of marine
invertebrate remains and of selachian bones or plates, or
the not infrequent intercalation of a bed of varying width
amongst typical marine dolomitic, chalk, or limestone de-
posits of great thickness, a careful study of the nature of
their deposits, of their included organisms, and of the bio-
logical relation of these to each other, reveals that Triassic
v^ertebrate life was still wholly freshwater, or that a very
few only of the predatory elasmobranchs and specially the
cestracionts were advancing seaward.

When comparison is made of the fish-fauna of the above
four divisions, throughout Europe, it becomes evident that
the older selachian groups which lingered on into the Per-
mian have entirely disappeared, the Elasmobranchii even
as a great class seem to have temporarily suffered an eclipse
alike in numbers and in species. And when introduced to
us again later on in the Lias, they are found to be fresh-
water forms which are increasingly developing a marine
environment. The Dipneustei are no longer represented
by Dipterus, Uronemiis or Sagenodiis of the Palaeozoic
epoch, but have evolved the genus Ceratodus that closely
resembled the Barramunda of Australia. The Chondro-
steans are wonderfully rich in types that are intermediate
between palaeozoic and upper mesozoic genera. The older
types of crossopterygians have entirely disappeared, and
in their places are Graphiiirus, Diplurus and Undina, all
freshwater in habitat.

Of the chondrostean "ganoids" that come Into marked
prominence, such genera as Dictyopyge, BeJonorhynchus,
Saurichthys, Semionotus, Colohodus, Heterolepidotus, Al-
lolepidottis, Pholidophonis, Thoracopterus, Pholidopleu-

176 Evolution and Distribution of Fishes

rus and Peltopleiinis were abundant, while the last four
were destined to become increasingly rich in species, special-
ly from the Rhaetic to the Liassic beds above. They all
swarmed in, and were confined to, the lakes and swamps of
the continental areas of the time.

The freshwater phyllopod Estheria minuta^ along with
allied Entomostraca, teemed in quiet waters of ponds or
pools, a fairly rich insect-life is indicated, though the ab-
sence as yet of colored flowers and of succulent fruits, gave
little occasion for the evolution of other than orthopterous,
neuropterous and hemipterous genera. Limulus^ as repre-
senting a condensed and modified derivative genus from
the once abundant eurypterids, was led up to by the curious-
ly intermediate Permian genus Prestwichia, but is still like
them of freshwater habitat.

In examining first the set of British rocks, it can be said
that a recognition of the freshwater character of such
strata as above mentioned has been repeatedly voiced by
not a few geologists. Thus in a joint paper by Newton and
Brodie {i2g: 537), after referring to "the unique specimen
of Dipteronotus cyphiis from the Bunter of Bromsgrove,"
the former author describes a new species as Semionotus
brodiei, and Brodie notes that his son obtained Palaeonis-
ciis {Dictyopyge as now viewed) superstes and a Semi-
onotus. On the slate on which the first specimens were
found were two impressions of footsteps of a large labyrin-
thodont. He then adds, "a similar stratum, with similar
fossils, occurs at several localities in Worcestershire. Foot-
prints of labyrinthodonts, generally of small size, are
occasionally found on the surface of the sandstones, and
at Rowington remains of plants in a very imperfect condi-
tion, among which is Voltzia in fructification, and some
small fruits resembling the Jurassic Carpolithus so-called."

Further on he notes the abundance of Estheriae in beds
of the Waterstones, and adds: "The Waterstones are
famous for the number (comprising nine genera) of sala-
mandroid batrachians, a large number and variety of which
have been found at Warwick, Leamington, and Coventry;
and a unique collection is preserved in Warwick museum."

During Triassic and Jurassic Periods 177

Succeeding to the above is a paper (750:542) by E.
Wilson "On the Triassic Beds at Colwick Woods," in which
he refers to abundant fish-remains from the transition beds
of the Waterstones of the Upper Keuper which at this point
rest on the basement beds of the Lower Keuper. He speaks
of "quite a shoal of the fishes, these often lying over each
other," and then adds "these deposits I believe to have
probably had a fluviatlle origin. The waterstones on the
other hand, (at the base of which the fishes occurred, and
to which series they belong) are regularly bedded fine-
grained sandstones and marls, showing ripple marks and
sun-cracks." In a footnote he says: "in these lowest beds
of the Waterstones at Colwick I found the stem of a land
plant, having the appearance of Equisetites columnaris and
probably allied thereto." He considered that the strata
"were evidently formed in waters which were tranquil, but
extremely shallow, and liable to entire or perhaps partial
desiccation. These waters were in all probability those
of saline lakes or lagoons" (but why saline? writer).
"Possibly the fishes found at Colwick may have become en-
trapped in the shallows of such a lake, and killed in numbers
by the drying up or the increasing salinity of the water."

L. J. Wills (757:28) confirms and in some respects
extends the above sets of results, while he gives a list of
organisms found by him in the sandstone and the shale
layers respectively thus :

I. THE sandstone. II. THE SHALE.

Plantae Plantae

Equisetites arenaceus Equisetites arenaceus

Zamites vogesiacus Zamites vogesiacus

Voltzia sp. also Coniferous wood Voltzia

Pj5Q£S Chiropteris digitata

Acrodus, spine of Arthropoda

Coprolite Estheria minuta

Amphibia p^^^^^
Labyrinthodont, tooth of

„ Dtpteronotus cyphus

Hyperodapedon

Again a series of papers by L. Richardson (752:374,
385,425; 755:385) deal mainly with the uppermost or
Rhaetic rocks. In the latter publication he gives a very
detailed sectional table, which shows that the Sully beds

178 Evolution and Distribution of Fishes

of the Lower Rhaetic were deposited as alternating fresh-
water and marine deposits with typical and quite distinct
fossils for each. Then follow some alternating layers of
black, shale and of bone beds rich in fish remains but all de-
void of marine organisms. Along with the fish, or in adja-
cent beds, abundant remains of Estheria miniita and a plant
Lycopodites are recorded. The fish remains include Acro-
dus minimus, Hybodus minor, H. cloacinus, Gyrolepis al-
berti, Saurichthys alberti, and Sargodon tomicus, the laby-
rinthodont Mastodonsaiiriis — that at once indicates fresh-
water conditions, — small teeth of Sphaerodus and "a man-
dible believed to belong to Palaeosaiiriis, as well as other
saurian remains."

The beds of the Upper Rhaetic seem to suggest a
marine invasion, but unless the above-named author has
mixed up contents of freshwater beds with these, the
presence with Pecten, Avicula, Pteria and Aviciiloidea, of
Gyrolepis scales suggests either that some hitherto fresh-
water species were slowly invading seashores, or as is much
more likely that the last were washed out from older strata
and redeposited in marine beds.

So apart from fishes, large amphibians and reptiles
allied to those of the Permian, like Mastodonsaiiriis, Tre-
matosaurus and Hyperodapedon, waded in the swamps, or
basked in the freshwaters, or progressed over the muds
deposited from recent freshets of the lakes or rivers. Thus
they left "footprints on the sands of time" that to-day
have enabled palaeontologists to distinguish many species,
even in absence of the animal remains. Such equally applies
to the reptiles, that now are represented by the three great
divisions of the crocodiles, the lizards, and the turtles.

First evidence of mammals is seen in the small form
Mtcrolestes, which once was regarded as a primitive mar-
supial, but as only fragmentary remains of the skull are
known, it may equally well have been a primitive mono-
treme.

In passing now to other regions where the Triassic was
represented by freshwater beds, it may first be well to in-
quire as to the possible extent geographically of the system.

During Triassic and Jurassic Periods 179

Fig. 23

i8o Evolution and Distribution of Fishes

The preceding chart (Fig. 23) sets forth the views of de
Lapparent and successors. It shows that two compact
expanses of dry land existed, such as might give opportunity
for migration and evolving adaptation of plant and animal
types over the greater part of what are now more or less
sharply separated continents. So, as during previous
epochs, one might expect to find a certain correlated simi-
larity in structural advance, in taxonomic affinity, and in
adaptation to environment of varying character. Such
also is largely true.

On the American continent, it is now agreed by geolo-
gists and palaeontologists that the Triassic drylands, fresh-
water lakes, and river systems with their flood-plains,
covered an extensive territory, that can still be fairly ac-
curately traced east of the Alleghanies from Canada to
the Gulf, also southward through Brazil to Chile and the
Falkland Isles. But so far as one can judge from fossil
remains, the geologic period represented, seems to be that
of the Upper Keuper and the Rhaetic of Europe. It may
therefore be that in the period between the Permian and
the Rhaetic extensive land denudation may have proceeded,
while marine strata were being enormously accumulated
in the west, from Alaska and British Columbia southward
to California and Idaho.

In contrast to his views on Devonian fish life Newberry
consistently advocated a freshwater or even more an estua-
rine environment, in his study of "Fossil Fishes and Fossil
Plants of the Triassic rocks of New Jersey and the Con-
necticut Valley" {1^4). These rocks, now usually known
as the Newark series, he regarded as having been laid down
during the latter half of the Triassic age, and so in the
Upper Keuper or in the Rhaetic period. They extend in
a north-east and south-west direction, parallel to the Al-
leghanies, and may represent the deposits laid down in
some great lake that extended from Nova Scotia to the
Carolinas, or even to the present Gulf of Mexico. The
deposit varies from 2000 to 5000 feet in thickness, and is
largely composed of red sandstones, shales and micaceous
deposits. Most of these are barren in fossils, or show only
scanty remains. We accept it that they were wholly fresh-

During Triassic and Jurassic Periods i8i

water, for while Newberry speaks of "estuaries," no trace
of a marine organism, nor of a mixture of freshwater and
marine organisms has been demonstrated.

But Newberry says "the Connecticut area includes layers
of nearly black shale charged with carbonaceous matter,
containing many remains of fishes and plants, and even some
thin films of coal. Also a small part of the series in New
Jersey consists of dark or dove-colored shales charged with
organic matter, sometimes crowded with the remains of
fishes and exhaling a marked bituminous odor when struck
with a hammer" (p. 4). In connection with the possible
origin of petroleum and natural gas the last statement is
most suggestive, as is also the following (p. 21): "The
layers of the shale which contain the largest number of
fishes are impregnated with bituminous matter, burning
for a time when thrown into the fire, and when struck with
a hammer giving off a peculiar odor. Similar fish-beds are
known to exist at Pompton, Plainfield, and beneath the trap
of the Palisades above Hoboken, and it seems probable that
the great mortality which strewed the bottom of the basin
at times with dead fishes was the result of some phase of
the volcanic action which poured out the trap-masses of
the Palisades and Newark mountains."

Lull (^55:397) in treating of "The Life of the Con-
necticut Trias" points out that the fishes all occur in two
bands of black bituminous shale, the lower of which rests
on a sheet of volcanic rock about 250 feet thick. The
shale is 50 feet to 100 feet thick and includes both plants
and fishes. Above it is a zone of shale 1000 feet thick with
dinosaur foot-prints. This is covered by a second sheet of
volcanic trap about 500 feet thick, and it again is covered
by a shale about 1200 feet thick with dinosaur footprints.
Above it is the second black bituminous shale about 100 feet
thick and enclosing plant also fish remains. Over this is
another trap sheet about 150 feet thick. Here, as in other
similar cases, we would suggest that the bituminous shales
represent volcanic dust deposits laid down in a shallow, but
extensive lake; that this ensured the fine preservation of
the fishes as shown by Eastman's illustrations, and that
the abundant petroleum oil resulted from destructive trans-

1 82 Evolution and Distribution of Fishes

formation of the natural fish oil when heated by the vol-
canic flows.

Chamberlin considered (5:111:9) ^hat the deposits
were of "shallow water or subaerial origin," the latter being
indicated by the numerous "ripple marks, sun-cracks, tracks
of land animals, etc."

Eastman, in "Triassic Fishes of Connecticut" {130: ),
says: "While there is nothing in the character of the fossil
fishes which would prove conclusively whether the deposits
were formed in salt or brakish or fresh water, the physical
character of the deposits, and the fossils other than fishes
found in them, make it substantially certain that the de-
posits are not marine. No corals, echinoderms, or brachio-
pods have been found in the Triassic in Connecticut or in
any other of the Triassic basins of eastern North America.
Molluscs are very few, and most of those found are un-
doubtedly fresh-water forms. A very few marine molluscs,
it is claimed, have been found in the Triassic of Pennsyl-
vania. A few Crustacea, probably freshwater or brakish-
water forms, have been found in some of the southern
Triassic basins, though not in Connecticut. A few insect
larvae have been found. For the rest the fossils of the
formation consist of land plants and tracks of reptiles and
amphibians, with a few skeletons of reptiles. Such an
assemblage of fossils makes it clear that the formation is
not marine, though the presence of a few marine shells (if
those shells are rightly identified) indicate conditions in
part estuarine."

The organic remains from this Newark series consist
of plants with aflinity to Carbo-Permian genera, but in the
cycadeous and coniferous forms approach much more nearly
to a later Mesozoic age. The animals are fishes, am-
phibians, reptiles, and — at Turner's Falls — apparently
birds. While fishes are abundant in various beds, amphibio-
reptilian animals are scant in their osseous remains, but
are often richly indicated by their footprints. These alone
proclaim that an abundant amphibian life — possibly de-
rived by evolution from the varied Carbo-Permlan amphi-
bian organisms of the Texan area — occupied the margins
of the lakes or river-plains, and this entirely agrees with the

During Triassic and Jurassic Periods 183

evidence noted below, that has been gathered from the
Western Triassic region.

The fishes recorded belong to the genera Semionottis
{Ischypterus of Egerton and Newberry), Catopterus,
Acentrophorus, Dictyopyge, Ptycholepis and Diplurus;
mainly members of the Chondrosteidae or sturgeon series.
While the genus Catopterus is, so far as known, peculiar
to Eastern American strata, Semionotiis and Dictyopyge
are common to Britain, Germany, Switzerland, South
Africa and Australia, Ptycholepis again includes seven
species, of which five occur in the Lias of England, one in
the Upper Trias of South East Europe, and one in the
Connecticut beds. Diplurus is a crossopterygian allied to
the more ancient Coelacanthus.

Over western North America, as in Europe, an exten-
sive marine and a nearly as extensive freshwater, series
of deposits took place during Triassic time. The former
now covers a wide area from Alaska southward through
British Columbia, California and Nevada on through
Mexico and southward to Chile. Over all of this the
Triassic sea laid down typical marine strata with equally
typical marine organisms, that included foraminifera,
corals, echinoids and crinoids, univalve and bivalve mol-
luscs, an exceptionally rich variety of ammonites and other
cephalopods, but no recorded vertebrate life.

The freshwater strata, as at present exposed, or left
after subsequent denudation, may have been developed more
or less continuously with the eastern deposits, over the
greater part of North America. Such a view is that in-
corporated in the chart of de Lapparent; and when we
think of the masses of freshwater strata now known to
occur in central and Northern Mexico, in North West
Texas, in Eastern California, and West Oklohoma there Is
much evidence in its favor. Not only so, a bridge In the
region of Honduras and eastward, may have connected
this northern expanse with a wide extension over eastern
South America. For in Brazil, the Argentine, and south-
ward to the Falkland Islands, wide areas exist where a
typical Triassic flora and freshwater or land fauna have
been traced.

184 Evolution and Distribution of Fishes

Further the striking similarity in genera, but distinct-
ness in species, of plant and animal — not least fish — re-
mains, shown between South America and South Africa
strongly indicate such an Americo-African connection as
DeLapparent figures. We need not here refer in detail
to the lists of plants from all of these localities, that indi-
cate a marked continuity in the Glossopteris flora, from
South America across Africa to Australia and even New
Zealand. It will suffice to state that the fauna fundamental-
ly shows a like continuity.

In South Africa the great mass of beds that collectively
has been called the Karoo formation was laid down accord-
ing to G. S. TI!orstorphine in a great inland lake (/J/: 123)
and seems to represent Upper Permian and Triassic beds.
According to Hatch and Corstorphine {1^8 : ig^) there
are three distinctly marked zones: (i) the uppermost or
Stormberg beds, that from their fossils suggest a cor-
responding age with the Eastern American beds; (2) the
Upper Karoo beds that may be of Bunter; and (3) the
Lower Karoo or Ecca beds of probable Permian age. These
authors give from the Stormberg a varied plant list of
"Glossopteris" type, such fishes as Ceratodus capensis, C.
kannemeyeri, Semionotus capensis and Cleithrolepis extoni.
Bain and Woodward (13Q : 239) add to these Palaeoniscus
bainii, P. sculptus^ and Dictyopyge draperi. An abundant
amphibio-reptilian life accompanies all of the above, while
Broom (7^0:30) has instituted an interesting comparison
between the Karoo genera of these beds and those recorded
from the Elgin sandstones of Scotland.

The affinities of the above-named African fishes — that
are all by descent and environment freshwater — are close
with species from the Upper Permian and the Triassic of
Europe and America. Thus Dictyopyge draperi links
North American, British and Swiss species, with others
' — given below — from the Upper Trias, of New South
Wales. Semionotus includes world-wide species of the
Trias; Cleithrolepis, so far as known, is common only to
South Africa and New South Wales. The teeth of Cerato-
dus recall those of allied species found only in freshwater

During Triassic and Jurassic Periods 185

strata from America through Europe to Africa, India, and
Australia.

As being of great importance from the physico-bio-
logical standpoint, Hatch and Corstorphine point out that
on top of the Stormberg beds, though doubtfully at what
particular time, great deposits of volcanic material were
thrown out, which in some places have a thickness of 4500
feet. Such enormous volcanic deposits must have caused
and accompanied tremendous alterations in land-areas,
wide-spread destruction to plant and animal life, constant
oscillations in land and water surfaces, as well as other
environal changes that would all aid in the evolution of new
species and genera, as well as the obliteration of others.

Neglecting Indian strata, that promise greatly more
for the future than the secured results indicate, attention
may now be given to Australian Triassic developments.
As set forth by Freeh these extend through Queensland,
Victoria and New South Wales, on even to the Island of
Tasmania, and are mainly if not wholly of freshwater
origin. Thanks to the efforts of A. S. Woodward, the fish-
fauna has received considerable attention {141 '. 10). The
general nature of the flora and fauna has been treated by
Etheridge and Feistmantel, who observe that plants and
fish are plentiful. Estheria coglani, as a native phyllopod,
persists through hundreds of feet of strata, while the two
labyrinthodonts Mastodonsaurus and Platyceps are associ-
ated. Feistmantel has given (7^2:40) a classified list of
the organisms found up to about 1890.

In Woodward's earlier communication on fishes from
Gosford rocks, Edgeworth David makes a preliminary
statement, in part as follows : "Although the shales as-
sociated with the fish-beds are probably partly tufaceous,
it is very improbable, to judge from the remarkable even-
ness and regularity of these strata, that the fish perished
through an inflow of volcanic mud, or the falling of a
shower of volcanic dust. The evidence quoted seems rather
to favor the supposition that the fish, which evidently lived
in some land-locked lake or sheltered estuary, where there
was not suflicient current to efface the ripple marks, and

1 86 Evolution and Distribution of Fishes

where delicate plants could be preserved in the fine muds,
were killed by the sudden silting up of the lake or estuary
with beds of coarse sand or gravel, swept down by powerful
floods of freshwater."

But Woodward in his later memoir {141: 10(1908)
when speaking of collections from the same formation, but
at St. Peters locality says: "The fish-remains obtained by
Mr. Dunstan from the Hawkesbury formation at St. Peters
belong to two distinct series, which are described separately
in the following memoir. The first and much the largest
series was discovered in a dark indurated shale, which splits
with a more or less irregular fracture; while the second
series was found in a grey mudstone closely resembling that
in which numerous fishes occur at Gosford. The skeletal
parts of the fishes in the first series are actually preserved,
though considerably stained and partly obscured by the
oxide of iron and manganese, with some pyrites."

"The fishes of the second series occur chiefly as im-
pressions on the rock, which are stained black zvith a thin
film of bituminous material, resulting from the decomposi-
tion of the original organic tissues. In both cases the fishes
appear to have been complete when buried, and show no
signs of having been disturbed by currents or by predaceous
animals. Like most well-preserved fossil fishes, they prob-
ably denote some local accident, which suddenly destroyed
and entombed them."

The writer would again suggest here that as such fish
would become putrid, softened, and disintegrated within
a week in freshwater, and as the fine mudstones indicate
no violent mode of detrital deposit in relation to the organ-
isms, death by volcanic shock or gaseous discharge took
place, with immediately succeeding entombment amid vol-
canic dust, either under water, or in shallow water that in
a day or two became dried up and sun-exposed. The whole
then probably firmed, and gradual exudation of oily
material sealed the organisms, as well as furnished the
chemical basis for transformation of their oils into bitumin-
ous products. Woodward has the following list from the
Gosford beds :

During Triassic and Jurassic Periods 187

Selachii. Sphenacantlius or ?.

Dipnoi. Gosfordia, a genus allied to but distinct from Con-

chopoma of Permian rocks, from Ctenodus of Palaeozoic

rocks, and Ceratodus of Mesozoic age.
Ganoidei. Myriolepis cla'rkei; M. latus, allied to the South

African Atherstonia.

Apateolepis australis, related to the Carboniferous genera
Plianerosteon and Actinophorus.

Dictyopyge illustrans, D. robusta, and D. symmetrica.

Belonorhynclitis gigas and B. gracilis.

Semionotus australis and S. tenuis.

Pristisomus gracilis, P. latus, and P. crassus.

Cleithrolepis granulatus and C ? latus.

Pholidophorus ? gregarius.

Peltopleurus ? dubius.

After an elaborate analysis and comparison with other
fish faunas he concludes: "So far as can be determined
from the fishes therefore, the Hawkesbury beds may be
regarded as homotaxial with the Keuper of Europe, or at
least with the Rhaetic, and on the whole the writer is
inclined to adopt the first of these interpretations." The
above list however suggests a curious admixture, of genera
peculiar to the strata such as Gosfordia, Myriolepis,
Apateolepis ; of others like Cleithrolepis that are common
to South Africa and Australia; and still others like Dictyo-
pyge, Semionotus and Pholidophorus that stretch across
the continents.

But that over the present area, a degree of separation
in time or space, may give rise to a very different fauna.
Is proved by the St. Peters list. This includes amongst
selachians Pleuracanthus parvidens ; amongst Dipnoi, Sage-
nodus laticeps; amongst Actlnopterygll Palaeoniscus crassus
and P. antipodeus, Elonichthys armatus, E. semilineatus,
Myriolepis pectinata, Elipsopholis dunstanii, Semionotus
formosus and Pholidophorus australis. Commenting on
the above Woodward Inclines to regard the group as of
Carbo-Permian affinity. But the presence of such typically
upper Triassic or Liassic genera as Semionotus and
Pholidophorus along with Palaeoniscus, would suggest
rather that this Australian area was a combining centre or
mixing place for older and newer elements derived from
other regions.

But In connection with our present fundamental con-
tention, Woodward's observations on the Dipnoi are most

i88 Evolution and Distribution of Fishes

important. He says : "The fragmentary skeleton of Sageno-
diis is of great interest when considered in connection with
other recent discoveries of extinct dipnoan fishes in Austra-
lia. There is now evidence of fore-runners of the surviving
Ceratodtis in the Devonian of New South Wales {Ganor-
hynchtis sussmilchi) , the Carboniferous of Victoria {Cten-
odus breviceps) , the Permo-Carboniferous and Triassic of
New South Wales {Gosfordia truncata), and the Jurassic
of Victoria {Ceratodiis aviis) . It is thus clear that Dipnoi
have always lived in the Australian region, and there is no
reason why Ceratodiis may not have evolved there." It
must be remembered however that Ceratodiis was once
practically world-wide, and that the richest and oldest
known centre for dipnoans was the British-Russian area
of the Lower Old Red. But the remarkable distribution
of the perennially freshwater group Dipnoi is one of the
outstanding proofs that some fishes have tenaceously clung
to their primitive environment.

The Jurassic Formation.

The Jurassic Formation is of surpassing interest from
the standpoint of fish-life. For it is in this that we again
have clear evidence of migration from a freshwater to a
marine life. Several factors seem to have cooperated to-
ward such a result. First, geologists are agreed that a
considerable — in some places great encroachment of the
sea on the Triassic and Permian land-areas took place,
which may be said to have reached an apparent climax in
our own day. During this shifting process great masses
of fishes became exterminated, while others became modi-
fied and adapted to changed environment. Second: this
evidently inclined many hitherto freshwater or anadromous
animals to adopt a semi-marine and eventually marine life,
through struggle for existence in the former areas along-
side evolving and formidable reptiles. Third: From being
rather unwieldy animals with — in many cases — a dentition
that was poorly adapted for combat and offensive destruc-
tion, one group of fishes — the Elasmobranchii — evolved
highly specialized catching, tearing and often in addition

During Triassic and Jurassic Periods 189

crushing teeth, that made them formidable antagonists.
Fourth: the body-covering of scales, the body-muscles, and
also the fins became of a highly perfected type In these.
Fifth: from having had few antagonists equal to or more
powerful than themselves in freshwater, as the Increasingly
huge carnivorous reptiles evolved, these evidently pressed
on the freshwater fishes, drove them to sea, and even then
many species and genera of reptiles — following the fish-
shoals — became modified as sea-dwellers. Sixth: the
abundant invertebrate life in the sea, that would serve as
suitable food, aided the persistence, multiplication and
•dissemination there of elasmobranchs. Seventh: consider-
able parts of subaerial areas, during the Permian and the
Triassic, became of a dry xerophytic and seml-desertic
nature, while simultaneously subject to considerable denuda-
tion, and to formation of wide lacustrine expanses that
often became shallow and saline. So not a few previously
freshwater organisms, — Including fishes, must have become
accustomed to a fairly saline environment. Preparation
was thus made for passage toward the sea of those types
which best survived in the saline environment. Eighth: the
climax of cephalopod development was reached during low-
er Jurassic time and then decreased. Possibly also medusoids,
related to those so beautifully preserved in the Solenhofen
slates may up to this time have been abundant and trouble-
some marine dwellers, but now may have begun to dwindle
In importance. Opportunity was thus at length given for
passage of the most predaceous or otherwise adapted, of
the freshwater fishes into the sea. The Selachians first, and
later lateral derivatives from the "ganoids" seized the
opportunity.

As emphasized by Sauvage {143: i) and other geolo-
gists and palaeontologists, the Rhaetic or Upper Triassic
beds pass almost insensibly Into those of the Liassic, while
we have already incidentally indicated that not a few plant
and animal genera are continuous through both formations.
But while extensive changes In the relation of land and
sea seem to have proceeded slowly during Triassic times,
oscillations between land and sea seem to have been fre-
quent and variable during the Jurassic. So marine or

190 Evolution and Distribution of Fishes

freshwater deposits on land surfaces often alternate in
close succession with each other. Biologically one result
of this was that — as in the case of Solenhofen slates — an
admixture of organisms may be entombed in what appears
to be a continuous rock mass of 40 to 80 feet in thickness.

Broadly it may be said that the first-deposited or Liassic
beds are in some areas wholly or largely freshwater — as
is true of the Lower Lias, — in others marine as is true often
of Mid-Liassic beds. The lower and middle Oolites are
largely marine, though in Europe the "Stonesfield Slates"
seem to be largely freshwater deposits. The upper or
"Portland Oolite," and the Purbeck that corresponds to the
Upper Jurassic of America, are of mixed character below
but largely freshwater above, while the lowest or Wealden
beds of the Cretaceous formation are essentially of fresh
water or land origin.

But before proceeding further it should now be stated
that a palaeontological classification of Jurassic and Cre-
taceous strata has come into vogue, which while undoubtedly
of great service in distinguishing marine strata, has tended
to throw into the background a true biological estimate
of the land and freshwater deposits of both formations.
Or even through the reporting loosely of two or more
groups of fossils from strata that are adjacent but quite
distinct in origin, correspondingly loose views have origi-
nated as to the true interpretation biologically of the
fossils. So while definite species of pelecypodous, gastero-
podous, or cephalopodous molluscs may be helpful strati-
graphic guides in determining marine horizons, if these
organisms are mixed, in tabulations, with organisms from
other and it may be adjacent freshwater beds, an obscure
or entirely incorrect view may be got as a whole. One of
the early and also careful observers in this respect is P. B.
Brodie, whose "History of Fossil Insects in the secondary
rocks of England (1845)" abounds in detailed classifica-
tions of strata with their typical fossils.

In trying therefore to obtain a correct picture of the
physico-biological aspects of the Jurassic, the writer pro-
poses first to refer to or directly quote, descriptions of
previous observers.

During Triassic and Jurassic Periods 191

In papers by Wright (i-f-fii^) and Roberts {143:-
229) extensive lists are given of marine invertebrate organ-
isms in appropriate strata, but no mention is made of fishes,
reptiles or mammals, all of which were then abundant over
land or lacustrine areas. In contrast to this Judd in "The
Secondary Rocks of Scotland" {146: gj) not only lists
abundant and typical marine fossils from lower Jurassic
rocks of the Moray Firth region, he further emphasizes the
freshwater nature of many strata, which he correlates
with the Portland, Purbeck and Wealden of Anglo-French
areas. They agree also in showing, not unfrequently, alter-
nations of freshwater and marine beds with their ap-
propriate fossils. But for the former beds he habitually
uses the expression "estuarine," to which the writer would
take exception, and replace by the name lacustrine. For
wherever a careful discrimination is made, the so-called
"estuarine" beds contain only freshwater fossils, or these
rarely mixed with what evidently were washed-out and re-
deposited oyster shells. For in referring (p. 103) to an
"argillaceous type of estuarine strata" that is made up
largely of finely laminated clays, he states that these clays
"contain also thin bands of limestone, sometimes crowded
with shells of Cyrena^ Unio, and other freshwater bivalves,
sometimes with Paludina and other freshwater univalves,
and at others made up of dwarfed Ostreae and other marine
shells, crowded together in masses, and forming beds
exactly resembling the well-known "Cinder-beds" of the
Purbeck. In these clays, beds crowded with the valves
of Cyprides and Estheriae also occur, with veritable bone-
bands, made up of scales and teeth of fishes and bones of
reptiles. Not unfrequently these clays are crowded with
plant-remains; and interstratified with them occur beds of
lignite or coal, sometimes several feet in thickness, some of
which have been worked with success."

"No one can examine these strata of the argillaceous
type without being at once struck with their resemblance to
those of the Purbeck formation, and also to those of similar
character which occur at the top of the Wealden in the
Isle of Wight and elsewhere, which I have described in
detail under the name of the Punfield Formation."

192 Evolution and Distribution of Fishes

But a small mass of strata along the Moray Firth shore
known as the Linksfield Slates, and that is of doubtful
Wealden, Purbeck or Rhaetic age, deserves attention from
its fossils. These he lists (p. 148) as follows:

* Femur of Trionyx sp. t Modiola hilliana
•Vertebrae of Plesiosaurus sp. f Modiola sp.
•Scales of Semionotus punctatus f/lstarte sp.

* Scales of Lepidotus minor * Unio sp.

* Scales of Pholidophorus sp. * Cyrena

•Scales of Eugnathus sp. * Cyclas (several species)

* Teeth of Hybodus laivsoni * Melanopsis sp.

* Teeth of Hybodus dubius * Paludina sp.
t Teeth of Sphenonchits martini * Planorbis sp.

* Acrodus sp. * Candona ? globosa

* Spines of Hybodus *Estheria minuia var brodieana
t Ostrea sp. t Spine of Echinoderm

f Pteroperna sp. * Neuropieris and other ferns

f Myiilus sp. * Fragments of wood.

Now as in the former case, so here, there is a sharply
marked set of lacustrine organisms, which we have indi-
cated by an *, as well as a set of marine remains indicated
thus f. And we venture to affirm that the two sets occur
in quite distinct, though it may be closely adjacent beds.
For all of the above fish remains had been up to this point,
and most of them remained, freshwater inhabitants. Acro-
dus and Hybodus alone were now wavering between a lake
and sea environment.

Partial proof of the above is got on p. 162, where he
gives the exact succession and thickness of beds at Strath-
steven, and here steady alternation of marine and lacustrine
beds, with their appropriate fossils, is evident. But on
p. 182 an evident mixing up of the two sets of organisms
is set forth in his list.

But in many lists of fossils from typically marine Juras-
sic strata, several genera of Cestracionts become increas-
ingly prominent alongside marine vertebrate organisms.
These are Hybodus^ Acrodus, Asteracanthus, and Stropho-
dus. The same is true, amongst chimaeroid selachians, of
the genera Myriacanthus, Squaloraja, Ischyodus, and
Ganodus. Unfortunately not a few of the species of these
genera are only known to us by their teeth, or by their teeth

During Triassic and Jurassic Periods 193

and spines. Hybodus (Figs. 24, 25) and Acrodus however
— which may be evolved representatives of the palaeozoic
Orodiis and Campodus, extend from the Trias to the Upper

Fig. 24. Hybodus hauffianus, restored view of fish, from Upper
Liassic bituminous shales of Wurtemburg. Fig. 25. Skeleton of
H. fraasi from Solenhofen slates. (After Campbell Brown).

Cretaceous, and were during Triassic times at least, partial-
ly if not wholly freshwater. But from the Lower Lias up-
ward to the close of the Jurassic, they evidently became
largely and at length wholly marine, and continued so till
their extinction in the late Cretaceous. The other genera
above named, that appeared first in Liassic or in Oolitic
strata, either died out during the Jurassic, or persisted in
marine surroundings to the close of the Cretaceous, as with
Ischyodus. Further a few Jurassic genera, like Squatina
(Fig. 26), Rhinohatiis,, and Cestracion, that had taken to
marine surroundings, continued alive in one or more species
up even to the present day.

So while it is possible to speak only with a fair degree
of accuracy, the evidence seems sufficient to warrant the

194 Evolution and Distribution of Fishes

Fig. 26. Squatina speciosa, an ancient type of ray-fish from the
lithographic stone of Solenhofen, Bavaria, a, mandible; b, pectoral
arch; c, pectoral fin; d, pelvic arch; e, pelvic fin. Two-thirds
natural size. (From A. S. Woodward).

Statement that after complete, or almost complete, oblitera-
tion of marine fishes in early Permian time, during the
Triassic or early Liassic days derivatives of the older
elasmobranchs that inhabited lakes, river beds and swamps,
again began to descend to the sea, where their descendants
are still a powerful and aggressive, though not very abund-
ant, group.

An equally abundant land flora, and land to freshwater
fauna, have been described and listed for central European

During Triassic and Jurassic Periods 195

beds. But the prominent feature is the varied lot of am-
phibious to marine reptiles that invaded or often swam on
the waters. A like condition is revealed by a considerable
thickness of the Stonesfield Slates and the Kimmeridge
clay. It is in this latter zone also that the remarkable Solen-
hofen and Cerin slates occur that are dealt with in consider-
able detail below, and the organisms of which give us a
fuller and more graphic idea of the life of this period,
than do any other known rocks of the entire geologic scale.

In some upper Portland beds, and in Purbeck sections
of central England, Brodie and others obtained rich organic
remains from a set of slaty limestones. In addition to land
plants, cyprids, a great variety of insects, several genera
of freshwater molluscs, and an important series of fish re-
mains were assembled. While a considerable number of
elasmobranch fishes like Hybodus and Acrodus still lived
in the lakes, the dipnoan and ganoid genera were greatly
more numerous, and in some localities their remains are
piled on each other. So in many places over the European
continent from England eastward, bituminous rocks that
contain decomposed products of these fishes are known.

Over the European continent extensive masses of
Jurassic freshwater beds have been treated of by Oppel
(7^7), by Quenstedt {148: i), also by Credner, Meyer,
PIctet, and others. But attention may now be given to
the remarkable Solenhofen-Eichstadt slates. The fish-
fauna of these was studied in succession by Agassiz, A.
Wagner, V. Meyer, Winckler, and V. Reis. But the
most complete and recent study is that of I. Walther en-
titled "Die Fauna der Solenhofener Plattenkalke" {149'-
135). The material composing these slates is an extremely
fine-grained and hard limestone that has attained inter-
national repute as yielding the finest grade of lithographic
stone. The deposit occurs in somewhat discontinuous
masses along the Wiesenthal of Bavaria, and varies from
20 ft. to nearly 80 ft. in thickness. It is readily divisible
into a series of layers {FUnze of Walther) that vary from
thin plates to blocks which average 10-15 cm. in thickness.
These split apart readily from each other, owing to delicate
films of deposit that are usually of darker and more earthy

196 Evolution and Distribution of Fishes

aspect than the hard lime rock. The enclosed organisms
are of most diverse character, but whether plants, medusae,
brittle-stars, echinoids, leeches, worms, crustaceans, mol-
luscs, fishes, reptiles or birds the finer structural details are
revealed often in marvellous manner. Further as grouped
by Walther they may roughly be divided into water and
land forms.

It becomes therefore a matter of special interest to
learn how such a deposit originated. Walther evidently
very correctly pictures, as a background setting and starting
point, the presence of a Kimmeridgean land-mass, into
which extends a lagoon or shallow arm of the Jurassic sea
that then covered large areas in Western Germany, France,
and East England. Coral reefs and islands dotted over
this sea, while through activity of the associated marine
organisms, those deep deposits of organic lime-carbonate
origin had formed which we know as the marine Liassic and
lower Oolitic strata.

But Walther then pictures a constant tendency to ele-
vation and depression of the lagoon that now is the Wies-
enthal, with resulting death and stranding of the organisms
near the surface of each deposit, when such by elevation
became dried in the sun. The wafting of dark-colored land
debris — inorganic and organic — gave rise to the separating
films that now cause parting of the layers (or flinze). Re-
newed depression of the lagoon area started another limey
deposit over its surface, that lasted till renewed elevation
took place. Sudden death of the organisms was effected,
owing to and simultaneously with, volcanic changes that
caused the elevation.

This view is an ingenious and attractive one, and further
seems well to fit the case, since Walther shows that the land-
derived animals were evidently mostly dead before being
embalmed in the strata, while the marine organisms — the
medusae, brittlestars, antedons, crustaceans, and some fishes
— were entombed in the living state. But for many reasons
the writer would suggest a different and much more efficient
explanation, one however which would doubtless have been
ruled out of court before publication of Russell's work.

During Triassic and Jurassic Periods 197

First. It should be observed from his grouping of beds
on p. 145 that different combinations or sets of organisms
are found at different localities; also that there may be
several zones for medusae, several for the fish Leptolepis,
several for reptiles, etc. In other words there is often a
successional repetition. Second: the land forms were main-
ly dead when entombed, the marine ones were alive.
Third: all were quickly and perfectly covered over and
encased. And here we might note specially regarding the
remains of the various genera of Medusae. The writer
has often watched myriads of these cast up on many shores
from Scotland to New Jersey and Florida. If left exposed
to drying sun and wind even for three hours practically no
trace is left of their organization. Again the brittlestars
were killed and covered before they attempted auto-dis-
organization. As Walther himself well puts it also (p. 206)
"no putrifactive bacteria destroyed the muscle of the fish,
no scavengering crabs had devoured the dead corpse."
Fourth: the entombing substance was quickly and evenly
deposited; was an extremely fine crystalline dust or a
watery crystalline deposit; and it quickly hardened into an
extremely close uniform fissile rock. Fifth: some rapidly
destructive substance, agency, or set of phenomena caused
far-reaching death in the air( as for the pterodactyls and
insects), in freshwater (as for the leeches and ganoid
fishes), and later in the sea (as for the medusae, brittle-
stars, etc). Sixth. These fine deposits of crystalline lime
substance were at irregular intervals covered by thin de-
posits of darker and apparently aerial debris. Seventh.
As Walther accepts and explains, both kinds of deposits
were not solution-precipitates, they seem to be made up
of extremely comminuted crystalline or isolated particles.

We would consider then that the entire Altmiihl-Solen-
hofen deposit represents a huge mass of coral rock-deposit
that was caught up by a volcano or volcanoes, ground up in
its vent during days, or even weeks of eruptions, crystalliz-
ed and then shot out over hundreds of miles of country. Vio-
lent winds, earthquakes, and poisonous gaseous discharges
meanwhile brought wholesale death to land or freshwater
animals; while the crystalline volcanic dust percolating

198 Evolution and Distribution of Fishes

downwards into the shallow waters of the now elevated
lagoon along with discharges of gases at each climax of
oscillation caused asphixiation of the marine organisms.

So, if we make use of the exact statistics gathered by
Bonney, Judd, and specially by I. C. Russell ( // : 284-296) ,
the entire deposit may have been made within a few days.
Or at most three or four main periods of activity, such as
Walther's photographs of the strata suggest, may have
occurred, each within a few weeks or possibly longer periods
of time apart, and each depositing four to twenty feet of
volcanic lime-dust produced from pulverized coral-rock.
The mention by Walther of four successive medusoid zones
(p. 210 of his work), and of several zones with abundant
Leptolepis fish remains favors such a view.

The revelation given by these Solenhofen beds of a rich
fish-life is probably unequalled by any other single rock
formation, if we except the even richer Monte Bolca de-
posits. Whole shoals of individuals belonging to the genus
Leptolepis must have perished in some freshwater area, and
been swept rapidly on as dead bodies where they became
spread out and entombed in sidewise manner. Some fishes
— probably by action of poisonous gases — had time to
disgorge their food before death; while others show small
fishes still in the alimentary canal, as with Caturus and
Thrissops, whose food seems largely tp have been the small
fry of Leptolepis.

As indicating the extreme richness of the fish-fauna thus
brought together we subjoin Walther's list in its entirety.
And as his combined results were gathered from various
localities along the Wiesenthal, each locality is indicated
by a capital letter that is the initial for the locality name.
These are Kelheim (K), Eichstadt (E), Solenhofen (S),
Mornsheim (M), Langenaltheim (L), Daiting (D) and
Nusplingen (N).

Elasmobranchii. Fain. Cestraciontidae.

Order Sqnalidae. f-m Acrodus falcifer, E. S. L.

Fam. Notidanidae Fam. Scyllidae.

m Notidanus eximius. m Palaeoscyilium formosum

E. D. N. E. S.

m Notidanus intermedins M. m Pristiurus eximius E.

m Notidanus serratus N. Fam. Lamnidae.

m Notidanus ^.cagneri S. m Sphenodus nitidus S.

During Triassic and Jurassic Periods 199

Fam. Squatinidae.

m Sqnatina alifera, E. S.

Fam. Rhinobatidae

m Spathobatis mirabilis E.

m Asterodermus platypterus
K. E. S.

m Asterodermus titanius K.
Order Holocephali.

m Ischyodus avitus, K.

m Ischyodus quenstedti,
K. L. S.

m Ischyodus schuebleri, K.

m Ischyodus suevicus N.

m Chimaeropsis paradoxa,
E. S.
Dipnoi. Wanting.
Gan'oidei.

Order Crossopterygii.

f Undina acutidens. Z.

f Undina minuta.

f Undina penicillata. K.E.Z.

f Libys polypterus, K.

f Libys superbus, K. Z.

f Coccoderma bavaricum.

i Coccoderma gigas.

f Coccoderma nudum.

f Coccoderma substriolatum.

f Coccoderma suevicum.
Order Heterocerci.

f Coccolepis bucklandi, E. S.
Order Lepidosteidae.

Fam. Stylodontidae.

f Heterostrophus latus, S.

f Heterostrophus lepidotus,
K.

Fam. Sphaerodontidae.

f Lepidotus armatus, S.

f Lepidotus decoratus, S.

f Lepidotus gigas, S.

f Lepidotus intermedius, K.

f Lepidotus maximus, K.E.S.

f Lepidotus notopterus, K.E.S.

f Lepidotus oblongus, E. S.

f Lepidotus pustulosus, S. D.

f Lepidotus subovatus.

f Lepidotus unguiculatus, D.

Fam. Saurodontidae.

f Eugnathus macrodon

f Eugnathus microlepidotus,
E. D. N.

f Pleuropholis laevissima, E.

f Pholidophorus dentatus, N.

f Pholidophorus intermedius.

f Pholidophorus macroceph-
alus, K. E.

f Pholidophorus latus, N.

f Pholidophorus micronyx,
K.

f Pholidophorus microps, S.

f Pholidophorus ovatus, E.

f Pholidophorus tenuistria-
tus, N.
Isopholis brevivelis, E.
Isopholis latimanus, K. E.
Isopholis muensteri, K.
Ophiopsis attenuata, E.
Ophiopsis intermedia.
Ophiopsis muensteri K.
Ophiopsis procera, S.
Ophiopsis serrata.
Eusemius beatae E.
Propterus denticulatus.
Propterus elongatus, E.
Propterus gracilis, E. S.
Propterus microstomus, E.
Propterus speciosus, E.
Propterus zieteni.
Notagogus denticulatus.
Histionotus oberndorferi,

K.
Macrosemius insignis, S.
Macrosemius latiusculus.
Macrosemius rostratus,

E. S.
Fam. Rhynchodontidae.

Aspidorhynchus acutiros-

tris (frequent).
Aspidorhynchus mandibu-

laris, K. E.
Aspidorhynchus obtusiros-

tris, E.
Belonostomus kochi, K.
Belonostomus muensteri,

D (frequent).
Belonostomus pygmaeus,^.
Belonostomus sphyrae-

noides, E. S. (Z?)
f-m Belonostomus tenuirostris,

E. S. (frequent).
Order Amiadae.

Fam. Pachycormidae.

Hypsocormus insignis,

K. E. S.
Hypsocormus macrodon,

K. E.
Sauropsis longimanus, E.
Diplolepis sp, E.
Agassizia titania, E.
Fam. Eugnathidae.

Caturus contractus. S.
Caturus cyprinoides, E.
Caturus elongatus, E. S.
Caturus furcatus,

K. E. S. L. D. N. C.
Caturus granulauts, K.
Caturus macrurus, E. S.
Caturus microchirus, E. S.
Caturus pachyurus,

K. E. S.
f Caturus subovatus.

200 Evolution and Distribution of Fishes

f Strobilodus giganteus,

E. S. N. K.
f Strobilodus siievicus, N.
f Liodesmus gracilis,

K. Z. E.
f Liodesmus sprattiformis, S.
f Eurycormus speciosus,

K. E. N.
f Callopterus agassizi, K. S.
f Oligopleurus cyprinoides,

K. C.
f Oenoscopus esocinus, K.
f Macrorhipis muensteri,

K.
f Macrorhipis striatissima,

K.
f Aethalion blainvillei, E.
f Aethalion crassus, E.
f Aethalion tenuis.
Fam. Amiadae.
f Megalurus altivelis.
f Megalurus brevicostatus,

K.
f Megalurus eiegantissimus.
f Megalurus elongatus.
f Megalurus grandis, E.
f Megalurus grandis, E.
f Megalurus lepidotus.
f Megalurus polyspondylus,

f Lophiurus minutus, E.
Order Pycnodontidae.

f Gyrodus hexagonus, S.
(frequent.)
Gyrodus macro pthalmus,

K. E.
Gyrodus platurus, S.
Gyrodus rugosus, K. S. N.
Gyrodus titanius,

K. S. D. N.
Microdon elegans, K. S.
f-m Mesodon heckeli, S.
f-m Mesodon macropterus,

E. C.
f-m Mesodon pulchellus, E.
m Mesturus verrucosus, K. E.
Teleostei

f Leptolepis knorri, E. S.
(frequent.)
Leptolepis macrolepidotus,

S.
Leptolepis polyspondylus,

E. S. C.
Leptolepis sprattiformis,

E. S. N.
Thrissops formosus, K. E.
Thrissops propterus, E.
Thrissops salmoneus,

K. E. S. D. C.
Thrissops subovatus, K.

f

The above includes a larger number of species than is
known from all of the other beds of the Jurassic system.
But as directly bearing on our present study, we may now
inquire as to which of these were probably freshwater and
which marine. In the above list the former are prefixed,
according to the present writer's views, by (f) before each
species or before each genus or larger group, if these are
all considered to be such; and by (m) before the latter.
This determination is based most largely on statistics and
evidence set forth in later chapters of this work, where
the groups and genera are specially treated. In part also
it is based on evidence furnished by the mass of associated
organisms that uniformly occur together.

On such a basis, and viewing the Jurassic as a whole,
we would regard as freshwater beds considerable strata
of the Lower and Upper Lias, of the Stonesfield slates, of
the Kimmeridgean, of the Portlandian to a less degree, and
of the Purbeck. With Woodward's "Museum" volumes
as an aid then, it seems that of freshwater species sixty

During Triassic and Jurassic Periods 201

are recorded from the Lower Lias, forty-three from the
Upper Lias, twenty-three from the Stonesfield Slate, one
hundred and forty-two from the Kimmeridge beds, of which
one hundred and thirty are included in the Solenhofen
list, fifteen occur mainly in the upper lacustrine Portlandian
strata, and forty-two in the Purbeck. In contrast, of
marine species the Mid Lias is practically destitute of
records, as are the Inferior Oolite and Fullers Earth. The
Great Oolite and Corn Brash contain species of Hybodus,
Acrodus, Aster acanthus and Strophodus. The typically
marine Oxfordian and Corallian beds include Notidanus
along with the four just named, as also Orthacanthus,
Mesodon, Mestunis and Microdon, the last three as de-
rivatives from freshwater types (p. 331), Hypsocormiis
and Aspidorhynchus (p. 341 ). Each of these is represented
by one to three species, rarely as with Notidanus In the
Corallian by four species.

But from the perfect state of preservation shown by
species of Squatina (Fig. 26, p. 194), Rhinohatus and
Belemnobatis in the lithographic slates of Bavaria, as
compared with many of the ganoids, these had probably
also become to a greater or less degree marine. Their
Increasing abundance also in marine beds of the Cretaceous
system likewise favors such a conclusion.

In stating the above then the writer considers that all
of the great groups of fishes continued as inhabitants of
the lakes, rivers and swamps, throughout the Jurassic and
into the Cretaceous, except for genera of the rays, the dog-
fishes, probably some of the pycnodonts like Mesodon and
Microdon^ also more doubtfully a few "ganoid" genera
like Hypsocormiis and Aspidorhynchus. But even the
earlier species of Hybodus and Acrodus that occur in the
Lias and Stonesfield Slate, were still largely lake-dwellers,
Thus Judd in treating of the Jurassic rocks of N. E. Scot-
land (Q. J. Geol. Soc. 29 (1873) 97) gives the thoroughly
freshwater list already quoted (p. 192).

The occurrence here of small specimens of Ostraea and
of Mytilus would indicate that occasional Invasions of sea-
water may have happened, or even that they had been
washed out and redeposited.

202 Evolution and Distribution of Fishes

But the apparent mixing of records for two adjacent
sets of beds, and the accurate placing of them for another
in adjoining sentences, is evidently set forth in de Lappar-
ent's work (<57 : 1 141-42). For on page 1141 he gives
from Mazenay in "calcaires fissiles" of the Jurassic,L^/)^o-
lepis constrictus and L. affinis — both of which we regard
as freshwater — along with Lioceras serpentinum and Ino-
ceramus c'mctiis, both typically marine. But at top of the
adjoining page he gives from Souabe in "schistes-bitumi-
neuse ou schistes-carton" five strata in descending order
thus :

(5) schistes a Belemnites tripartitus et Inocerames.

(4) schiste et calcaire a Lioceras serpentinum et Belemnites

gracilis.
(3) Calcaire a poissons {Ptychodus, Leptolepis, Lepidotus) .
(2) feuillet a Posidonia Bronni.
(i) couche de passage a Monotis substriata.

The two upper and the lowest at least are typically marine
beds. (3) and (2) however are freshwater. Ptychodus
moreover is a Cretaceous not Jurassic genus. One of those
oscillations between land and sea evidently occurred here,
such as were frequent through the entire Jurassic.

A very similar state of affairs is that set down by
Brodie (pp. 57-58), where he described a "bone-bed" with
associated PuUastra arenicola, but when in an exact tabu-
lated list he states that this bone-bed is "a hard thin stratum
full of pyrites, and composed of bones, scales, and teeth
of fish," and that "connected with this is a white and yellow
sandstone full of casts of PuUastra arenicola'* we recognize
that the two were totally distinct. The latter was a marine
bed, then above it and doubtless after sudden elevation
of the region and probably by volcanic dust-deposit, a mass
of freshwater fish-remains became entombed, these fishes
agreeing with species that de Lapparent often refers to
amid typical freshwater setting.

A suggestive paper by Roberts "On the Correlation
of the Upper Jurassic rocks of the Swiss Jura with those
of England" contains extensive lists for Mid and Upper
Jura. These include varied and abundant marine inverte-
brates, but not a single plant remain, Estheria or fish. But
passing to the Purbeck strata on top of the series he gives

During Triassic and Jurassic Periods 203

Chara, Cypris, Bithynia, Planorbis, Corhula^ and Hyd-
robia, along with teeth scales and bones of fishes, all of
which he regards as freshwater.

J. V. Rohon {16:1) gives a valuable glimpse into
freshwater beds that he and Heer regard as of Upper
Liassic age, and which are exposed on the Angara river
north of Irkutsk in Siberia. In contrast to the extensive

Fig. 27

Fig. 27. Dapedius politus, a freshwater Lower Liassic ganoid
fish from Dorset, England. Fig. 28, restoration of the skeleton;
both one-fourth natural size. (After A. S. Woodward).

204 Evolution and Distribution of Fishes

lists that Neumayr, Nikitin and Pavlow give for higher
and typical marine beds of the Jurassic in which fish remains
are unmentioned, Rohon gives sixty-three species of plants,
twenty-three of insects, various remains of crustaceans, and
a few species of fish, probably belonging to the genus
PhoUdophonis, as determined by A. S. Woodward.

In the "Kota" beds of the Deccan, India, Sykes
(750:272), (757:8:23; 9:351; 10:371) and Egerton
have described a succession of strata that appear to be
transition beds from the Upper Triassic to the Lower Juras-
sic and which are largely or wholly freshwater in origin.
In a rock section about forty feet thick Bell records the
alternation of five layers of bituminous shale with limestones
or dark shales. From the shale Bell and Egerton (757:
10:371) have described Daped'nis egertoni, that is allied
to the South English Liassic species D. politus (Figs. 27,
28), Lepidotus longiceps, L. breviceps and L. deccanensis,
while the latter further observes that "the specimens of bitu-
minous shales contain besides the fish remains, some copro-
lites and some traces of plants." In the later paper it is
noted that the fish remains are associated with abundance of
Estheria mangaliensis, the dipnoan Ceratodus, also with
Brachyops laticeps and Hyperodapedon. All of these were
contemporaneous with a rich Gondwana flora, and are clear-
ly freshwater.

But as showing how readily incorrect views may be
developed, when Sykes recorded L. deccanensis^ he at once
concluded that this must be a marine form, and so suggested
that it was "indicative of the former submerged state of
the Peninsula of India." Taken in conjunction with Eger-
ton's later observation on the geographical distribution of
Lepidotus (757: 10:373), ^^^ ^^^ other associated organ-
isms, it indicates that a lake-bed, or extensive river flood-
plain, existed then amid the dry land of the Indian massif.

As in all preceding formations so for the Jurassic it will
be observed that bituminous shales or bituminous rocks of
some kind are usually recorded wherever a rich fish fauna
exists; and it is undoubtedly still in connection with accumu-
lations of freshwater — not marine — fishes that these bitu-
minous products are associated. In the preceding context

During Triassic and Jurassic Periods 205

mention of such has been made in the strata of the "Kota"
beds of India, while others might further have been in-
cluded. Further Mansell-Pleydell in speaking on "The
Geology of Dorset" (75^:408) says: "The Kimmerldge
Clay of the vale of Blackmore is less bituminous than that
of the Kimmeridge district; where it is upwards of sixty
feet thick, and strongly impregnated with bitumen, giving
off a disagreeable smell. It burns vividly with a bright and
clear flame, but is unfit for ordinary use as fuel. . . It
has an unpleasant odor when burning, resembling petro-
leum, and yields a reddish ash. The volatile matter of the
richer beds is upwards of 73%; the solid mineral matter
being only 27%."

Finally a noteworthy study on the Australian Jurassic
is A. S. Woodward's "Fossil Fishes of the Talbragar Beds
of Australia," that may be of Kimmerldgean age. In a pre-
liminary notice by T. W. E. David and E. F. Pitmann it is
said: "the fish-beds proper form the lowest of the three
members into which, on lithological grounds, the deposit
to which they belong may be divided. They consist of lami-
nated hard siliceous shales, cherty in places, rendered ochre-
ous by ferruginous infiltrations and traversed by joints"
"Fish and plants are so abundant that it is difficult to find
even a small fragment of the shales devoid of them. The
plants are preserved in the form of siliceous impressions,
their pure white color contrasting strongly with the ochre-
ous tint of the enclosing shale." The plants included are
Thinnfeldia odontopteroides, Podozamites lanceolatus,
Neiiropteridiufti australe, and Taeniopteris daintreei.
Associated with them and with the fishes was a cicadeous
insect. The perfect condition of the plants, the insects,
and the fishes, suggests one of two possible modes of origin
for the rocks and the state of the organisms. Either they
became suddenly entombed and cased up by siliceous vol-
canic dust, or some siliceous thermal lake area, by sudden
bursting and discharge of its contents, killed and enclosed
the organisms intact. Future detailed study may yet settle
the question.

The fishes as determined by Woodward are of excep-
tional interest in the present inquiry. They Include a species

2o6 Evolution and Distribution of Fishes

of Coelacanthiis, Coccolepis australis, Aetheolepis mirahilis,
Archaeomaene tenuis, and A. rohustus, Leptolepis talbra-
garensis, L. lowii, and L. gregarius. The association of
insects and plants, as well as the complete absence of any
marine organisms, stamp the deposit and the fishes as fresh-
water. But the occurrence of fossilized shoals of the first-
named Leptolepis, at once recalls Walther's description of
L. sprattiformis in the Solenhofen Slates. Again in speak-
ing of Coccolepis Woodward says : "The genus thus de-
fined is represented by small species in the lithographic stone
(Lower Kimmeridgean) of Bavaria {Coccolepis buck-
landii), and in the Purbeck beds and Lower Lias of
England. It is therefore of much interest to find a large
fish in the Hawkesbury-Wianamatta series of Talbragar,
exhibiting characters so similar as not to be more than
specifically distinguishable."

Aphnelepis, in its near relation to Semionotus and
Aetheolepis,, and as a specialized ally of the Liassic Dape-
dius, serves with the above to link the Australian and
European fish-fauna in close manner. As to the preserva-
tion of these, and as shedding some light on the Solenhofen
shales, the author says : "The fishes are crowded together
as if suddenly destroyed and very few of them have become
disintegrated before fossilization. A glance at the ac-
companying plates will show how beautifully even the most
delicate bones and fin-rays are usually preserved." In des-
cribing and figuring the scales alike of Aetheolepis and
Archaeomaene he also demonstrates the graded continuity
shown (Fig. 54, p. 330) from a ganoid to a perfect
cycloid type. If to this we add the close anatomical struc-
ture of these and of related genera to primitive and de-
rived teleosteans, that were, like these, dwellers in fresh-
water, a clear way is opened for understanding how and
where primitive teleosteans first evolved, and why it is that
a large proportion of these are still freshwater. It explains
also how derivative types, during subsequent Cretaceous
and Tertiary times, gradually passed into and stocked the
seas and oceans with what are now the dominant fishes, both
as regards genera and individuals.

During Triassic and Jurassic Periods 207

So In the evolution of the great families Pholidophorl-
dae, Oligopleurldae and Leptolepidae, a definite and easy
transition Is made, during the period from the upper Trias-
sic to the close of the Jurassic, from the ancient Proto-
spondylll or scaled ganoids to the great group of the Teleo-
stei that was destined gradually to displace all of the other
groups In individuals. In genera, In geographic distribution,
and In adaptive contrivances.

2o8 Evolution and Distribution of Fishes

CHAPTER VIL

The Physical and Biological Environment of Fishes.
(d) During the Cretaceous Period

The fundamental changes in distribution of land and
sea, that were effected toward the close of the Liassic
period and that became even more pronounced as subse-
quent Jurassic deposits were laid down, proceeded with
equally striking results during Cretaceous time. The dia-
gram on p. 240 shows this for the later Cretaceous.
The period is an important one in our present inquiry.
For all accumulated evidence combines to show that a great
and varied extension of elasmobranchs into the sea now
took place. It also emphasizes the viev/ that the Dipnoans,
most of the Holosteans, the Chondrosteans, and lingering
Crossopterygians, as well as many of the derivative Teleo-
steans remained as freshwater dwellers.

Here also it may be observed that the only genera of
the fishes which occur in Jurassic strata and have come down
through the Cretaceous to our own day in living repre-
sentatives are Rhina [Squatina) , Rhinobatus, Notidanus,
Cestracion, Pristhiriis^ and Ceratodiis^ all of which except
the last are finely preserved in the Solenhofen slates, and
all had apparently become thoroughly marine by the be-
ginning of the Cretaceous, except Ceratodiis^ which per-
sisted throughout in freshwater.

The Cretaceous vegetation was in many places luxuriant
and even sufficed to furnish workable coal. Such coal beds
also are practically always associated with strata that indi-
cate inland lacustrine conditions. Thus the Wealden coal
of North West Germany, and to a less extent of England;
the Deister coal beds of North West Germany, the Pflan-
zen-quader of Bohemia; the enormous beds of the Laramie
formation, that are estimated to include "more than
100,000 square miles of coal-bearing land" (5:111: 159),
are a few examples.

The marine strata, as now known, have bulked more
largely in geological literature, than the freshwater or

During the Cretaceous Period 209

terrestrial, and the fossils have correspondingly been em-
phasized. Broadly speaking the lowest or Wealden and
the Neocomian beds of Central Europe, that seem exactly
to correspond with the Comanchean and Dakota beds of
North America, are largely freshwater, and often show
direct continuity with the Purbeck or Upper Jurassic below.
The Greensand-Gaults of England, the Aptian-Cenomanian
of France, the Flammenmergel and Lower Planer of
Germany, and the Benton-Niobrara-Pierre-Foxhill groups
of North America are wholly or largely marine. The Chalk
strata of England, the Turonian-Senonian of France, and
the Middle-Upper Planer of Germany are probably inferior
in position to the Laramie of North America, though in
saying this the writer does not forget the controversies over
the age of the last. These strata are either balanced be-
tween freshwater and marine beds, or somewhat preponde-
rate toward the latter. The chart on p. 211 sets forth the
supposed correlation relation.

Two important and fundamental changes were largely
consummated during this period, and undoubtedly affected
organisms powerfully. First: during the Lower Cretace-
ous period in South Africa and in western America great
volcanic activity proceeded, but this was, so to speak, the
prelude to greatly more catastrophic action during the Later
Cretaceous in India, in South Africa, and in Western
America. Thus the enormous deposits of volcanic rock in
the Deccan, that are 4,000 feet to 6,000 feet thick, cover
an area of at least 200,000 square miles. The "Laramide"
rocks of Dana cover a large part of Western America and
indicate tremendous volcanic action.

Regarding this entire area Geikie (/ill: 1374) says:
"At the close of the Jurassic period, the first great up-
heavals took place. Two lofty ranges of mountains — the
Sierra Nevada (now with summits more than 14,000 feet
high) and the Wasatch — 400 miles apart, were pushed up
from the great subsiding area. These movements were
followed by a prolonged subsidence, during which Cretace-
ous sediments accumulated over the Rocky Mountain region
to a depth of 9000 feet or more. Then came another vast
uplift, whereby the Cretaceous sediments were elevated

2IO Evolution and Distribution of Fishes

into the crests of the Mountains, and a parallel coast-range
was formed fronting the Pacific. Intense metamorphism of
the Cretaceous rocks is stated to have taken place. The
Rocky Mountains, with the elevated tableland from which
they rise, now permanently raised above the sea, were
gradually elevated to their present height. Vast lakes
filled depressions among them, in which, and on the plains
in front of the mountains, as in the Tertiary basins of the
Alps, and the Gondwana series of the Himalaya, enormous
masses of sediment accumulated. The slopes of the land
were clothed with an abundant vegetation, in which we may
trace the ancestors of many of the living trees of North
America. One of the most striking features in the later
phases of this history was the outpouring of great floods
of trachyte, basalt, and other lavas from many points and
fissures over a vast space of the Rocky Mountains and the
tracts lying to the West. In the Snake River region alone
the basalts have a depth of 700 to 1000 feet, over an area
of 300 miles in breadth."

Such profound changes in the surface-crust of the earth
not only originated some of the loftiest mountain chains of
the world, they must also have served by cosmic stress and
strain to deepen the ocean areas, and give to these greater
fixity of position. During the process a gradual breaking up
and rearrangement of two great continental masses Arcto-
gaea and Notogaea evidently proceeded from this time
on to the Miocene period, when the present main outlines
of land and sea were effected.

Second, With increased ridging up or elevation into
mountain chains — really high land-waves or crumplings
before denudation became conspicuous — of the land, the
waters of the earth would become increasingly restricted to
oceanic areas. So the extensive marshes, freshwater lakes,
and wide lagoon-rivers, would correspondingly become re-
duced in extent. These two conditions however would
be eminently favorable for, and would emphasize, pro-
gressive evolutionary changes in organisms. For they
would bring into sharp prominence the effects of isolation
of organisms; of new or changed environal states; of in-
creased littoral, sea, and ocean areas, in which originally

During the Cretaceous Period

211

freshwater and later anadromous types of animal might in-
creasingly multiply after they became marine dwellers, as
well as other important biological and ecological factors.
And one of the prominent results was the continued and
increasingly abundant migration of elasmobranch fishes, and
now even more of evolving teleost fishes, from a previous
freshwater to an acquired marine environment.

Already we have seen that during the Jurassic period
various selachian, cestraciont, pycnodont, and pachycormid
fishes had branched off from freshwater ancestry into
marine life. But during the Cretaceous period, derivative
types from the freshwater "ganoids" gradually became
modified, in a manner that is traced in subsequent chapters,
along two lines of environal adaptation. One very large
and important series remained amid freshwaters, but rapid-
ly evolved into teleosteans of varied affinities and increas-
ingly perfected structure. Another, and at first less numer-
ous series, evolving also into teleostean types, passed into
seashores, later into the deep sea, and ultimately into
oceans and ocean depths. Exposed there to diverse en-
vironal conditions they evolved, through proenvironal and
selective reaction, modifications that, at the present day,
have culminated in forms often of grotesque, weird or de-
fensive aspect and structure. These are considered in de-
tail in chapters XII and XIII.

Formation

N. America

England

France

Germany

Lebanon

Laramie

Fox Hills

Fort Pierre

Niobrara-
Benton

Graneros
Dakota

Norwich
Chalk

Danian

Chapelle Marl

Upper
Cretaceous

Upper Chalk
Middle Chalk

Lower Chalk

Senonian
Turonian

Cenomanian

Quader

Upper Planer
Middle Planer

Lower Planer

Senonian

Turonian

(a) Sahel

(b) Hakel

Lower Chalk

Lower
Cretaceous

or
Comanchean

Horsetown

Kootenay-
Knoxville

Potomac

Gault

Greensand
Up. Wealden

Lo. Wealden

Albian

Aptian
Neocomian

Flammen-

mergel

Gargasmergel

Urgonian
Weald Clay

Deister

Nubian
sandstone

Neocomian

212 Evolution and Distribution of Fishes

As we now have to deal biologically with the two great
sets of freshwater and marine fishes, as well as some that
seem to have been more or less anadromous in habit, the
preceding chart may aid in correlation of the beds dealt
with in the countries where the Cretaceous is most carefully
studied. But it must be understood that the correlation is
an attempted effort toward scientific exactness, but may
be in time considerably modified.

Beginning with the lowest beds that make up the Weal-
den formation, this has generally been conceded as of
freshwater origin But Geikie (7:11:940), Chamberlin
{8: III: 128), and others have regarded the entire English
deposit as having been laid down in a large "delta 20,000
or 30,000 square miles in extent." Many considerations
however militate against this. Thus delta deposits are
typically irregular, interbedded, and devoid of uniform
organic strata, those of the Wealden are largely clays that
indicate steady precipitation in still waters, and which have
definite organismal zones; delta deposits are restricted to
narrow and irregular channels which are interrupted by
land masses between, those of the Wealden are extended
and agree surprisingly well with those of the American
Potomac, as well as of the Weald of North Germany.

The writer would therefore favor the explanation given
by C. J. A. Meyer in his paper "On the Wealden as a
fluvio-lacustrine formation" {i^S- 243). He adduces good
evidence for the view that the freshwater Purbeck beds are
uniformly continuous with the base of the Wealden; that
the Wealden strata were mainly laid down in shallow lakes
that seem at times to have dried up over considerable areas
so as to cause sun-cracks; that such remains as fruits of
Chara, in addition to the abundant fern, equisetum, cycad,
coniferous fossils previously recorded, also the varied
invertebrate organisms like Cypris, Unto, Physa^ Pahidina,
and Planorbis^ likewise the freshwater fishes and amphib-
ians already known all indicate a fluvio-lacustrine environ-
ment. He therefore concludes:

(i) That the Wealden strata are a fluvio-lacustrine
rather than a purely fluviatile or fluvio-estuarine deposit.

During the Cretaceous Period 213

(2) That the Wealden rivers continued in existence,
although probably in much diminished volume, during the
accumulation of most of the succeeding Neocomian strata.

Meyer however considers that occasional marine in-
trusions took place, and so gave rise to the deposits with
Ostraea, Mytilus and similar marine organisms. He further
states that "the higher beds of the Wealden are not only
extremely uniform in character, proving to some extent
their deep-water origin, but also contain freshwater fossils
up to their very junction with the Neocomian strata. Speak-
ing also of the passage beds and of the Lower Neocomian,
he says, quoting Fitton, that these include "a large quantity
of a kind of gravel, containing numerous fragments of fish
bones. It is just such an accumulation of sediment as would
result from the dispersion of shore deposits over the floor
of a moderately deep lake." He also regards the "Pun-
field" formation of the Isle of Wight as Upper Wealden,
and adds: "The occurrence of a Spanish fauna at Punfield
proves, if it proves anything, that the Neocomian (Lower
Greensand) series of the southeast of England and of
Eastern Spain are, in point of age, equivalent deposits."

The writer is compelled also to take an exactly opposite
view from A. S. Woodward (756:69) when he writes:
"The Wealden estuary seems to have been the last refuge
of the Jurassic marine fish fauna in this part of the world."
All exact evidence shows that such Wealden fishes as
Hybodus, Acrodus, Aster acanthus, Neorhombolepis, Coel-
odus, and Belonostomus, were either once freshwater or
derivative marine descendants therefrom, that reached the
sea during Jurassic times. For previous to that time no
sure commingling of marine invertebrate remains, with
fishes that lived alongside them, is known since early
Permian time onward, while up to this time Hybodus and
Acrodus occur occasionally still in freshwater relation.

Resembling the Wealden of England, and probably
continuous in time, as they are in facies and organic remains,
beds occur over a considerable part of North Germany that
Geikie (/rH: 1203) summarizes as follows: "Below the
Hils-thon in Westphalia, the Harz, and Hanover, the lower
parts of the true marine Neocomian series are replaced by

2 14 Evolution and Distribution of Fishes

a massive fluviatile formation corresponding to the English
Wealden, and divisible into two groups: First, Deister
Sandstone (150 feet), like the Hastings sand of England,
consisting of fine light-yellow or grey sandstone (forming
a good building material), dark shales, and seams of coal
varying from mere partings up to workable seams of three,
and even more than six feet in thickness. These strata are
full of remains of terrestrial vegetation [Equisetiim,
Baiera, Oleandridium, Laccopteris, Sagenopteris, Anomo-
zamites, Pterophyllum, Podozamites and a few Conifers)
also shells of freshwater genera {Cyrena, Fivipartis,
Cyprids), and remains of Lepidotus and other fishes;
Second, Weald Clay (65-100 feet), with thin layers of
limy sandstone {Cyrena, Unio, Vtviparus, Melania, Cypris,
etc.)." It will be observed that there is no indication of
estuarine or semimarine organisms in this list, and so we
would regard all, as in the case of the English Wealden, as
of lacustrine origin.

But with the close of the Wealden period, or in some
places during Neocomian times, wide areas that are now
dry land, became submerged to a greater or less degree
below sea level, and over these areas the Upper Greensands
and zones of chalk were deposited. The invertebrate life
at that time must have been extremely rich, as every list of
marine fossils testifies. But mixed amongst these in increas-
ing quantity and variety are the remains of fishes. These
consist chiefly of teeth, jaws, scales, or spines — more rarely
of the partial or entire body — of selachian, cestraciont,
chimaeroid, or more rarely of teleostean types. These,
descending from the lakes or rivers, during Triassic and
still more during Jurassic times, became now the prevailing
groups of marine fishes, and likewise from their offensive
and defensive armature, must have proved formidable an-
tagonists to the medusae, the cephalopods, and the evolving
higher marine crustaceans of that time.

But from such primitive Jurassic freshwater genera
of pycnodonts as Mesodon, Athrodon, and Microdon de-
rivative marine genera like Pycnodiis, Anomoeodiis, and
Coelodus, arose in later Jurassic times, and reached a
climax in the mid or upper Cretaceous period. Then they

During the Cretaceous Period 215

began rapidly to dwindle toward extinction in the Upper
Eocene.

Alongside both of these, moreover, various derivative
offshoots of freshwater teleosts, which — as traced in
chapter VI — had themselves originated from more ancient
and primitive "ganoids," were now adapted to a marine
environment. These included some large powerful and
voracious fishes like Poi-theus (Fig. 29, p. 227), Ichthyo-
dectes, and Enchodus, as well as others listed in later
tables (p. 226).

The abundant primitive freshwater elasmobranchs of
late Old Red or Carboniferous age, like Acanthodes and
Pleuracanthus, were all elongate fusiform in shape, and
were much better provided with defensive spines, as well
as offensive teeth, than their congeners of other groups.
But after reaching a high specialization as fusiform types,
or after evolving into flattened types like Ctenacanthus and
Janassa respectively, amid marine environment, these, as
well as great groups of their freshwater ancestors were
obliterated wholesale during the Permian period and only
slowly recovered in freshwater, still more slowly sent out
derivatives into the sea in Jurassic time. The last again
evolved into two similar main lines as before — the fusiform
series or Squalidae, and the flattened series or Raiadae,
The former of these two retained on the whole the fusiform
body, the lithe movements, and the predaceous habits of
their preexisting freshwater ancestors; the latter became —
through intermediate types like Rhina or Squat'tna (Fig.
26, p. 194) and Rhinobatiis of probable Jurassic origin,
modified into flattened ground-feeders of highly specialized
body-structure, like Raja — the skates — and Cyclobatis both
first known to us from Upper Cretaceous rocks.

In England the earlier works of Agassiz, Mantell,
Dixon and E. T. Newton on the Sussex and related beds,
but specially the elaborate work of A. S. Woodward on
"Fossil Fishes of the English Chalk" {157) illustrate how
richly the sea had become populated with elasmobranch
and chimaeroid species, also that chondrosteans allied to
the sturgeon as well as teleosteans of several families, were
abundant over a sea that covered the south-east part of the

2i6 Evolution and Distribution of Fishes

country. The corresponding memoirs of W. von der Marck
(756': v: II, 22,31 ) for the Upper Cretaceous of West-
phalia; of Reuss (75^:98), Geinitz {160) and Fritsch
{161) for Bohemia demonstrated like conditions for central
Europe. Those of Bassani {162: 15), Davis (/65:457)
and Pictet {164) for Italy and Mt, Lebanon; of Leidy,
Cope, Williston, Stewart (/<^5:385), Loomis {166) and
others for the extensive Benton-Niobrara and related beds
in central North America, all prove widespread invasion of
the sea that was started almost wholly in late Jurassic times,
but became highly accentuated in the Upper Cretaceous
epoch.

Such comparative distributional tables also as those
of A. S. Woodward for the strata of Lebanon and England
(7(57:471), and of A. S. Stewart (Op. supra) for the
Niobrara strata of Kansas, as compared with those of
European, West Asiatic, and other localities are most
instructive. Thus Dercetis is shown to be common to Mt.
Lebanon, to Wurtemberg, to England, and to the United
States. Sardinius is common to all of the above except
England; Spaniodon occurs in Mt. Lebanon and the United
States; while other equally striking distributional facts ap-
pear. Some of these are discussed, and a possible natural
explanation is given, in future chapters. So the presence
of marine invertebrate fossils, side by side with the skele-
tons, teeth, scales, or spines of teleost, pycnodont, cestraci-
ont, or selachian fishes, is now a common happening of
marine Cretaceous strata.

But that even over the above areas, where heavy chalk
deposits had formed, an elevation of land might again give
rise to freshwater lakes, with their typical fossilized organ-
isms, has been shown clearly to have taken place. Thus over
extensive parts of central Europe marine deposits of Ceno-
manian age were succeeded by beds that locally are known
as "Pflanzen-Quader." These not only contain abundant
remains of elm, ash, laurel and other dicotyledonous trees,
but the flora has been so abundant as to give rise to carbon-
aceous shales, or to thin beds, or even thick beds of coal.
The absence of marine organisms among these remains
is sufficient proof that the sea had for the time retreated.

During the Cretaceous Period 217

A significant feature of the marine beds with their in-
vertebrate organisms, and evolving marine fishes, is the
total absence of amphibians which have always and wholly
frequented freshwater or the land. Thus if one overhaul
the classified list prepared by the Committee of the British
Association {168: 149) or similar more recent lists, one
notices that while various amphibian genera are listed from
Carboniferous, Permian, Triassic, Keuper, Bunter and
other rocks of freshwater origin, none are found mixed
with marine types.

In marked contrast to this was the formidable invasion
of the sea by saurians, that were undoubtedly land dwellers
in their earlier origin and history, but which from Jurassic
and onward to early Cretaceous days passed seaward, and
underwent striking modifications there. ^ Most of the
Plesiosauria and Pterosauria, so far as evidence shows, re-
mained from Triassic to Cretaceous time as land, air or
lake dwellers, and then died out. But many had a formid-
able organization for preying on other animals. These
and succeeding derivative marine reptiles preyed heavily
on fishes, as their coprolites demonstrate. So not a few
of the fishes per force took to a marine life. And this
biological relation it is, which we would with all caution
advance, as the main explanation for the migration seaward
of many groups of fishes, during late Jurassic and early
Cretaceous times. Then such a genus as Elasmosaurus
amongst Plesiosaurians, which in some of its species largely
remained on land or in freshwater, also the entire group
of the Ichthyosauria, and of the Pythonomorpha in their
later history, followed the fishes seaward, and became
remarkably modified accordingly. The formidable rows of
teeth that they developed, the often elongated snout along
which these were disposed, the spiral valve of the intestine,
the crushed remains of cephalopods and of fishes often
found fossilized in their digestive tract, and the complete
modification as well as condensation of the limbs after the
pattern of a cetacean, all demonstrate that they were form-
idable sea animals and could pass to a great distance from
land in search of prey.

2i8 Evolution and Distribution of Fishes

It seems not unlikely, therefore, that the comparatively
sudden reduction in variety, in genera, and in individuals
of the hitherto dominant group of the Cephalopoda, was
largely brought about by the passage into the sea of car-
nivorous selachians, cestracionts, and teleost fishes, which
had themselves been driven from lakes, rivers and deep
marshes by evolving carnivorous reptiles, and in time be-
came the agents for destruction of the cephalopods. Still
later, in the battles that often took place — as fossil evi-
dence shows — between individuals of the evolving fresh-
water reptiles, whole groups migrated to the seashore and
into the sea. There they devoured alike the cephalo-
pods and the fishes. Thus Cope says of the giant snake-
like Elasmosaiirus that it "probably often swam many feet
below the surface, raising the head to the distant air for a
breath, then withdrawing it and exploring the depths 40
feet below without altering the position of its body. It
must have wandered far from land, and that many kinds
of fishes formed its food is shown by the teeth and scales
found in the position of its stomach."

A new environal factor deserves further to be empha-
sized, as it probably contributed more or less to migration
seaward both of fishes and some reptiles. We refer to the
evolution of winged reptiles, and still later of birds. From
present evidence, both of these must have been evolving in
late Triassic and early Jurassic days. For already abund-
ant remains of the winged reptiles are met with in Liassic
freshwater rocks, and of birds from the Solenhofen Slates
onward. The former reached their climax of development
in the early or mid Cretaceous and had disappeared by the
end of that epoch. Provided with great stretch of wing
in relation to body-size, with powerful jaws holding equally
powerful teeth, they would be able to attack fish from a
new centre of action. Like the Ichthyosaurians also they
gradually carried their attack to sea-shores during Mid-
Cretaceous time. Their constant presence then as a hover-
ing foe, at first over inland waters, and later over seashores,
must have contributed to the seaward passage of fishes.

The wading, and even more importantly the large div-
ing, birds of this epoch such as Hesperornis, must have been

During the Cretaceous Period 219

as formidable and destructive for fish-life as were the ptero-
dactyls, and like the latter they became proficient sea-
hunters.

Though the subject is more fully discussed in a later
chapter, reference might here be made to the evolutionary
derivation of the earliest teleostean fishes. As has been
generally accepted by leading ichthyologists of the past
quarter century or even longer, these were all derived from
holostean freshwater ancestry. In some cases, for example
as with the highly specialized pycnodont fishes — primitively
freshwater genera like Mesodon and Athrodon of the Lias,
Stonesfield Slate, Kimmeridge Clay and Purbeck strata,
passed seaward as bottom feeders, and without originating
more dominant forms, became purely marine dwellers, like
Anomoeodiis, Palaeobalistum and Pycnodus of marine Cre-
taceous and Eocene age. Unadapted in body, in fins, in
teeth, and in general build for successful defense, not to say
offense, they died out in Upper Eocene times.

In contrast to the last, derivative forms of the Eugna-
thidae, Pachycormidae, Aspidorhynchidae, Semionotidae,
and Leptolepidae passed seaward during late Jurassic or
early Cretaceous times, and started the first teleostean in-
vasion there. Still other and even more abundant repre-
sentatives of the Semionotidae, Pholidophoridae, and Lep-
tolepidae varied by slow degree and multiplied abundantly
in lakes, as the progenitors of our existing freshwater teleo-
stean groups.

As illustrating the trend of events during the Jurassic
and Cretaceous periods, the following sketch might here
be given of what seems to be a progressive and continuous
evolutionary line of fish-modification, from Triassic to late
Cretaceous age. The ganoid genus Semionotus became
widely spread over the world from the early to late Trias-
sic, and this wholly in freshwaters. By gradual reduction
of the fin-fulcra, of the bones in the mandible, of the basal
plates in the pectoral fins, of the intestinal spiral valve,
and by decussation of the optic nerves, transition is made
to the Pholidophoridae.

The species of Pholidophorus were also freshwater,
and extended from the Keuper and Rhaetic or upper beds

220 Evolution and Distribution of Fishes

of the Triassic, upward to the Purbeck or mid-upper beds
of the Jurassic. These again led to the Leptolepidae, and
in regard to the last Woodward {i6g :lntrod. p. XIX)
says: "as already observed by Agassiz, the genus Pholido-
phorus exhibits a very close resemblance to Leptolepis in
general aspect, the osteology of the head being remarkably
similar, vertebral rings being tolerably well ossified, the fin-
fulcra very small and usually lost, while the scales are often
extremely thin and deeply overlapping though for the most
part united by a peg-and-socket articulation; and it is note-
worthy that no identifications of splenial and coronoid
elements have hitherto been discovered in the jaw."

In the Leptolepidae the fin-fulca have been absorbed,
the bones of the mandible have condensed to two elements,
the spiral intestinal valve has nearly or wholly been absorb-
ed, intermuscular bones — absent in the last — gradually
developed in OUgopleurus and are large in Leptolepis,
while a faint trace of ganoine often persists on the exposed
part of each scale. The genus Leptolepis extends from the
Lias upward through the Stonesfield Slates of England
and the Wianamatta of Australia, on through the Kim-
meridge and Purbeck periods to the Cretalceous. The
division then seems gradually to have broken up into several
groups, the Diplomystidae, Clupeidae, Elopidae, and Albu-
lidae, most of which passed seaward during late Cretaceous
or early Eocene time, though some persisted in their old
environment. Even now however, most of them are shore
dwellers, while the shad and allied types still return to
brakish or freshwater in the spawning season. A further
study of these is given on p. 348.

The flora of the Cretaceous period is as suggestive in
character as are the fish, the amphibian and the reptilian
faunas. For it is from the base of the system upward, that
an increasingly extensive array of angiospermic flowering
plants appears. By a set of combined characters, that it
would be out of place to discuss here, these in time became
dominant over the gymnosperms and fern allies, until by
the Eocene period they were highly conspicuous. Coeval
with them appeared those types of insect, like the bees,

During the Cretaceous Period 221

wasps, butterflies, and moths that aid in cross pollination
of flowers which bear colored floral parts.

The extensive and intercontinental volcanic disturbances
already referred to as occurring toward the close of the
Lower Cretaceous, not only started marked invasions of the
sea in some places, they seem also to have so created bar-
riers against the ocean, and to have so diverted long river-
courses, that great inland lakes were created, in which an
abundant fish-life might flourish. One of the most extensive
and earliest of these in the Cretaceous was the centre for
deposition of the freshwater strata of the Dakota forma-
tion in western North America. Regarding this Chamber-
lin-Salisbury (5:111:144) say: "The Dakota formation
is present over the great plains generally, though buried
over the greater part of the area. It extends westward
beyond the eastern ranges of the western mountains, though
in the mountain region, the area of deposition was greatly
interrupted by elevations which rose above the lakes,
marshes, or river flats where the sedimentation took place.
In Northern Montana, it is not known west of the Rocky
Mountains. The original eastern boundary of the forma-
tion is not known, for erosion has removed it from con-
siderable areas which it once occupied. Remnants of the
formation are now exposed, as far east as eastern Iowa
and Minnesota. It must have originally covered an area
1,000 miles wide and 2,000 miles long, within the United
States."

"The Dakota formation has commonly been regarded
as a lacustrine formation, deposited during an epoch of
crustal oscillation, during which the depth of the basin in-
creased. The necessity for postulating numerous oscilla-
tions and nice adjustments, is largely removed, if the forma-
tion be regarded as the joint product of subaerial and
fluviatile deposition, for deposits of this class furnish their
own adjustments. The presence of bird-tracks in the
Dakota of Kansas, and the preservation of some 500 species
of plant fossils, mostly the leaves of angiosperms, at
various points and in conditions which forbid much trans-
portation, imply the prevalence of subaerial conditions to
a notable extent at least.

222 Evolution and Distribution of Fishes

"The thickness of the formation is, on the whole, rather
uniform, averaging perhaps 200 or 300 feet, though greater
thicknesses are known. To the South (Texas) the Dakota
formation rests on the Comanchean system unconformably.
Farther north it is often in apparent conformity with the
Comanchean, though it often, as in the Wasatch and Uinta
Mountains, rests on older formations." (op.cit.pp. 145-46).

While the sea seems to have made great inroads on
the land, during most of the Upper Cretaceous, and furnish-
ed wide opportunity for migration into it, and evolution in
it, of races of elasmobranch and teleost fishes, a gradual
readjustment took place, with corresponding reformation
in late Cretaceous of lakes that rivalled those of the earlier
or Lower Cretaceous. One of the most extensive of these
again was that over the bed of which the Laramie strata
were laid down in Western America. These strata vary
in thickness from 1000 to 5000 feet, and from the conjoint
researches of L. F. Ward, of White, of Cope, of Dawson
and of Tyrrell, the lake or lakes became the centre for pres-
ervation of a varied flora, of a mammalian fauna that was
mainly marsupial, of a remarkable avian and reptilian
fauna, of a fish fauna described mainly by Cope, and of a
rich freshwater molluscan fauna.

In India and elsewhere, deposits of like extent and
history can be traced.

When such facts as the above are correlated, it will be
seen that the Cretaceous formation is by no means the pre-
dominating marine one that geologists and palaeontologists
have often supposed. One great reason for the latter
view has been that multitudes of the marine organisms
found as fossils readily lent themselves to fossilization amid
the deposits in which they are embedded. Thus the fora-
minifera, the corals, the crinoids, echinoids and starfishes,
the crustaceans, and the molluscs, were — as is usually true of
marine invertebrate life — prodigiously abundant, and be-
came quickly preserved in calcareous rocks. Readily lend-
ing themselves also to the work of the systematist, they have
been elaborately described and figured, often at the ex-
pense of higher types that require more discrimination in
study.

During the Cretaceous Period 223

The Cretaceous however, like the other formations
already studied, is often characterized by bituminous
material around fish remains, and in some parts of the
world by rich reservoirs of gas, oil, bitumen or asphalt.
Probably the richest bituminous centres are in central and
north-central North America. The deposits however of
this material have a new significance and importance in our
present study. For while we would consider that all of
the supplies from older formations — the Silurian, Old Red,
Carboniferous, Permian and Triassic, probably also largely
the Jurassic — were derived from analyzed fatty oils of
freshwater fishes, it seems now to be as clearly and largely
derived from marine fishes of Cretaceous age. Thus Fenne-
man in describing the Cretaceous oil-field of Boulder, Colo.
(770:322) says: "practically the entire mesozoic group
is represented in this district, and most of it is of interest
in the study of the oil." Again Eldridge, Prosser, Logan,
Williston and Adams amongst other investigators have
examined the oil fields of Kansas, Oklahoma, N. E. Texas
and Arkansas.*

Reference to the table of correlation on p. 211 will
show that over the above region the Potomac formation
forms the base of the system, and that above it are the
Knoxville, Kootenay, and Horsetown. Together these
form the Comanchean system and have a varying thickness
of 2000 to 6000 feet. They are made up of beds in part
of freshwater, in part of marine origin. The basal part
of the Potomac is the Trinity group of beds, rich in fish
and invertebrate marine fossils. These beds also contain
rich bituminous supplies.

But the Upper Cretaceous is specially noteworthy. For
the Benton and Niobrara series are both of marine origin;
the former at least is extremely rich in bituminous products;
and the strata, in particular the lower beds known as the
Mowry shales, are in places crowded with fish-remains of
marine habitat. Often the fishes are surrounded by oily
products, as if the latter were still in contact with the

The writer treats in detail regarding the above question in his volume, "Fishes the
Source of Petroleum," (1923).

224 Evolution and Distribution of Fishes

primary source of its supply. At times it is difficult to
determine whether the petroleum has originated in a fish-
bearing stratum and still remains there, or whether it has
not risen from such stratum, through porous ones overlying,
to become eventually sealed up in some porous sandstone or
sandy shale that covers the whole. Thus Adams (///: 38),
in treating of the eastern Texan region, records bituminous
clay-shale of Benton age. But from the Niobrara beds
above (that he calls Austin chalk) he separates off the
"Taylor Marls" that are largely made up of oil and gas
bearing sandstones. It seems not unlikely that the products
however came from Benton strata below.

Prosser, Logan, and Williston {172) have given
detailed study to the corresponding Kansan beds. Here
also the Benton and Niobrara series are specially important.
Logan in describing the Benton series divides it into seven
minor systems, and in most of these abundant fish remains,
oysters, Inoceramus and other marine organisms occur
amongst bituminous strata. Some of the Kansan Benton-
Niobrara beds are very richly bituminous, and Williston
(p. 243) after taking note of the "abundant marine inverte-
brates" says: "The Niobrara deposits have been famous
for the past twenty-five years for the abundance, variety
and perfection of its vertebrate remains." Of fishes there
is an extraordinary abundance of their remains, while six
genera of Mosasaurus were frequent. In the upper beds,
that possibly correspond to the "Taylor marls," of Adams,
he further indicates that Turtles, abundant Plesiosaurs,
and toothed birds occurred, since the seas then had evident-
ly become shallower, while Logan and Williston alike em-
phasize squalodont and cestraciont elasmobranchs as being
profusely represented by their remains. The wealth and
variety of teleosts in the Kansan cretaceous rocks is well
set forth in Stewart's (op.cit. p. 386) and Loomis' (op.
cit pp. 213-282) lists. Stewart's comparative tables also of
American and Europeo-Asiatic genera (pp. 387-389) are
highly instructive.

But in Canada the Cretaceous is likewise known to be as-
sociated with petroleum products. For, speaking of the

During the Cretaceous Period 225

Dakota sandstones of Alberta, Canada, Redwood (25:
125) says: "The Dakota sandstones at the base of the
Cretaceous series is saturated, over an area of at least
1,000 sq. miles, with inspissated petroleum, and is often
mentioned as the Tar Sand. It rests unconformably on
the Devonian limestones and shales, which are also petro-
liferous to a slight extent within the province, and abundant-
ly so both northwards in Mackenzie, and southward in
Ontario and the United States, so that the idea has found
favor in some minds that the Tar of the Dakota sandstone
is derivative from the Devonian series. But the latter, where
seen along the Athabaska and its tributary valleys, cut down
through the soft Cretaceous rocks, is devoid of any trace
of bitumen. It may be added that the Dakota beds are
petroliferous in other regions, where no such derivation is
conceivably possible." The above Canadian beds, in geolo-
gic position and petroleum yield, may correspond to the
Trinity beds of Eldridge and other authors. But the
writer would regard the Mowry shales, that lie toward the
base of the Benton series, as the more likely source of sup-
plies. This he has discussed in another work {173)-

In face of the above evidence, the writer would consider
that with passage of numerous elasmobranchs, — perhaps
more importantly of ganoids, and of teleost descendants
from freshwater ganoids — into a marine environment, myri-
ads of these were at times destroyed by some sudden and
widespread cataclysmic action, were covered over within
at most a week to a few weeks, and in time gave rise to
marine supplies of fish oil, which in turn by destructive
analysis produced those petroleum supplies that man is now
utilizing. A like result is dealt with in next chapter for
Tertiary strata and Tertiary fishes.

In a succeeding chapter detailed comparison will be
made of the genera and families of fishes that character-
ized respectively the freshwater and the marine strata of
Cretaceous age. But as furnishing a vivid picture of the
varied marine genera of teleosts, the writer subjoins a
table of these, prepared by A. Stewart (op.cit. 386) and
this also sets forth their stratigraphic relations.

226 Evolution and Distribution of Fishes

Cretaceous Marine

Teleosts

Benton
Beds

Niobrara Fort Pierre
Beds Beds

Foxhills

Recent

Anogmius .
Apsopelix .
*Beryx
Cimolichthys
Cladocyclus
Dercetis
Empo
Enchodus
Gillicus
Ichthyodectes
Ichthyotringa
Ischyrhiza .
Leptecodon
Leptichthys
Oricardinus
Pachyrhizodus
Pelycorapis .
Protosphyraena
Saurodon
Saurocephalus
Sardinius
Spaniodon .
Stratodus
Syllaemus .
Triaenaspis
Tetheodus .
Xiphactinus (Portheus)

* The determination of the above is probably incorrect. (See Woodward, Brit. Mus.
Cata. IV (1901) 386).

Of the Saurodontidae alone in the above list Stewart
says: "This family embraced some of the largest physo-
stomous fishes of the Cretaceous period of North America,
and from the size of the jaws and the powerful dentition,
we may suppose that they rivalled the Mosasaurs, the
smaller ones at least, in strength and ferocity," The skull
of Portheus (Xiphactinus) shown in Fig. 29, after Stewart,
illustrates well the above observations.

But about twice as many other genera have been de-
scribed from beds in England, Germany and from the
Hakel-Sahel beds of Lebanon. So between 80 and 90 marine
teleostean genera are thus known. Some of these deposits
have long been celebrated for the beauty and delicacy in
detail of the enclosed organisms. This is specially true of
those from the Benton-Niobrara of Kansas, the Sussex
beds of England, those of Westphalia, and the celebrated
Turonian or Sahel-Hakel beds of Lebanon. Even tender

During the Cretaceous Period

22.7

228 Evolution and Distribution of Fishes

and small fishes cover slabs in teeming numbers and show
finest bones of the skeleton in position as during life. Thus
J. W. Davis in describing the chalk rocks of Mount Leban-
on ( 765 : 45 I ) observes that there is a hard and soft chalk.
In the former the details even of ordinarily quickly-rotting
selachians are brought out with great distinctness; while
he further states that: "The hard chalk of Hakei is prin-
cipally remarkable for the immense number of fishes found
between some of the layers composing it. Hundreds of
the small Leptosomus macriirus are preserved on slates
occupying a few square feet and some other species are
proportionately numerous." As to the location of these
beds he considers that "the upper beds of the Turonian
group contain the fish-remains which have made the locality
famous in ichthyological annals." The increasingly special-
ized structure that some of the marine teleosts of those beds

Fig. 30. Ctenothrissa vexillifer. From the marine Upper
Cretaceous beds of Hakel, Mount Lebanon. Slightly enlarged.
(After Woodward).

show — not least in fin formation — is well illustrated in Fig-
ure 30 of Ctenothrissa from the Hakel bed of Mount Leb-
anon, and in Figure 31 of Chirothrix from the Sahel bed of
the same region.

During the Cretaceous Period

229

Fig. 31. Chirothrix lihanicus, a soft-finned or actinopterygian
marine fish from Upper Cretaceous rocks of Sahel Alma, Mount
Lebanon. About two-thirds natural size. (After Woodward).

Now it deserves to be pointed out that the above very
rich and also finely preserved remains of Cretaceous fishes
occur in what seems to be nearly the same horizon, viz. in
the beds of the Benton-Niobrara in Central America, in
the upper or Terebratulina-Holaster-Micraster beds of the
Middle Chalk of England {157), the top of the Mittel
planer (Mittel-quader) or base of the Ober-planer (Plat-
tenkalk) of Germany, and in the upper Turonian beds of
Mount Lebanon. All of these represent the Upper Turo-
nian zone with the characteristic Inoceramus labiatus, and
while it would be premature as yet to suggest that they form
a continuous and coeval sheet of deposit, it can at least be
said that similar or even identical genera of fishes extended
over the above area, and were so similarly destroyed in
preservative material that delicate fishes, as well as soft
tissues of large fishes, stand out in clear detail. Such also
would suggest that some common environal factors were
at work to produce like results.

Attention might here be drawn to the valuable correla-
tion-papers by Marck {158: ss)^ Woodward {I6'/^.^'^l)

230 Evolution and Distribution of Fishes

and Stewart (^^5:385), in which a comparison of the
various fish genera from two or more localities is made.

But though the above details are impressive, they must
by no means prevent us from realizing that this entire
marine association of fishes represents derivative offshoots
from more primitive freshwater elasmobranchs, ganoids,
or teleosts. Further a very abundant freshwater fish fauna
co-existed with them. For we have ample evidence that a
few elasmobranchs, all of the Dipneustei, most of the
"ganoids," and a very large series of the more primitive
teleosts remained in freshwater habitats. These will be
studied in detail later, but here it need only be observed that
over a large part of North America, not to mention other
continental areas, after deposition of the marine Fox Hills
group, there succeeded the Montana, Laramie and Living-
stone that represent several thousand feet of strata laid
down mainly in great inland lakes. The land surrounding
these was in large measure covered by a very rich flora in
part of gymnospermic, in part of angiospermic character.
An equally abundant insect, molluscan, and vertebrate fauna
occurred on the land or teemed in the lakes. Amongst the
vertebrates were many ganoid and teleostean fishes, turtles,
crocodiles and other giant reptiles.

Widespread volcanic activity, with corresponding de-
struction of plant and animal life, took place over widely
apart regions of the earth during later Cretaceous time.
This along with the steady evolution of predaceous and
ferocious vertebrates, also the steady spread of plant and
animal parasites that must often, as now, have caused havoc
to higher forms explains the great blotting out of life, as
passage is made from upper Cretaceous to lower Eocene
beds. Striking verification of this Is given later (p. 231).
But the uniformity and continuity of bedding seen in some
regions indicate that similar biological continuity was pos-
sible, though doubtless this was accompanied by steady
variation and new envlronal adaptations.

From Eocene to Recent Time 231

CHAPTER VIII.

The Physical and Biological Environment of Fishes.
Eocene to Recent.

In beginning our study of the relation of fishes to en-
vironal conditions during deposition of the Tertiary rocks,
a fundamental fact to be again remembered is the steady
or rapid alteration in land and water areas that resulted
in new geographical configurations. These culminated dur-
ing late Pliocene and Pleistocene time in the main conti-
nental masses and outlines that we now see. Such changes
were due to an increased soldification and thickening of the
earth's crust; to the extrusion of those enormous igneous
beds in India, Africa, America and to a less degree in other
regions, that were referred to in last chapter; and to the
resulting upheaval during Eocene to late Miocene time of
the most elevated mountain chains that now exist. As a
coeval result and in large measure also as a result of exten-
sive earth shrinkage or diastrophism, great cracks, faults,
downthrows and upthrusts, as well as foldings, caused a
breaking up of previous continuous land-masses over the
South Atlantis, the North Atlantis, "Lemuria" and other
regions, which in turn started profound organic change and
destruction as well as evolution.

While it is true that over wide areas in North America,
in south-east Europe and elsewhere, there is a gradual
merging and conformability of upper Cretaceous strata,
as they pass into the lowermost Eocene beds above, it is
more usual to find that marked alterations and uncon-
formabilities occur. And this is in line with the fact that a
tremendous and rapid obliteration of organisms — not least
of fishes — took place during transition from Senonian and
Danian, in other ^ords from Upper Cretaceous, to lower
Eocene beds. So, as Woodward's descriptions show, very
few genera of freshwater Cretaceous fishes are continued di-
rectly into Eocene. The number of marine genera however
is somewhat greater. By some writers it has been claimed
that the fundamental change seen in organic life indicated

232 Evolution and Distribution of Fishes

the lapse of "a vast period" during which slow variation
as well as obliteration were effected. While we would by
no means minimize the need for extended geologic time
the evidences rather are that enormous and rapid move-
ments of the earth's crust at once extinguished great cohorts
of organisms, and also caused the relatively few that were
left to vary rapidly and strikingly, as they passed into
new environal territory; or as they often became cut off
from continuity-association with other individuals of their
species; and as they then became adapted by proenvironal
response to their new surroundings.

When it is fully recognized that such changes did occur,
and that the ocean was gradually stocked with its groups
of marine fishes, by steady migration of these out of fresh-
water areas into the sea, and from late Jurassic time till
now, problems that otherwise seem confused and even in-
explicable, become relatively simple, as later pages will
explain.

With the progressive upheaval of mountain masses,
from late Cretaceous to the close of Miocene times, that
greatly excelled in height and bulk any that had previously
been formed over the earth's crust, greatly accelerated
denudation changes must have progressed over dry lands,
especially over those in proximity to, and sloping rather
abruptly from, the mountain ranges. This also would favor
the expanse and damming up of river courses, the conse-
quent formation of extensive lakes, the origin of changed
environal states, and resulting modification of the denizens
of the lakes and rivers. The great tracts that were covered
by lakewaters in N. W. America, in East Brazil, in central
Africa, in central and west Europe, in Tasmania and other
lands are proofs that such took place.

I. Eocene Formation. Restricting attention first to
the Eocene formation, extensive freshwater and marine
deposits are now known that enable us to form a fair idea
of general environal relations. The at times gradual, at
times sudden, change from the one type of deposit to the
other, tells that slow or rapid elevation or depression of
the land was proceeding in many regions, some of which
are touched on below. Whether such was due to volcanic

From Eocene to Recent Time

233

agency, to earth shrinkage and crustal flexures, or to local-
ized weighting of the crust by sedimentary deposits, need
not now concern us.

The lowest stage of the freshwater Eocene strata has
variously been called the Wasatch in western North
America, the London Clay in England, the Suessonian in
France, the Liburnian in Germany, the Hypsiprimnus beds
in Tasmania.

But the frequent intercalation of marine beds in most
of these shows that terrestrial oscillations were proceeding.
The Wasatch beds of north-west America were evidently
formed in a great inland lake, called by Cope the Wasatch
Lake, having a length at least of about 500 miles, and a
maximum width of 300. These beds may be as much as
4000 feet thick, and have yielded a varied vertebrate fauna.
The corresponding London Clay was in part freshwater,
in part marine, and the same is true of deposits over mid
and east continental Europe.

Above the Lower Eocene in central North America
are the extensive Mid-Eocene Green River and Bridger
beds of about 2000 feet average thickness, and that are
probably wholly lacustrine in origin. These are extremely
rich in vertebrate remains, especially mammalian.

Fig. 33.

Fig. 32. Amia calva. A surviving North American fish of the
group Holostei, the earliest known ancestors of which occur in
freshwater Eocene beds of Wyoming and adjacent states.

Fig. 33. Skeleton of the same fish, that shows close structural
relation to some Telcosts. (After Brown Goode and Franque).

234 Evolution and Distribution of Fishes

But Leidy (77^:184) and Cope (i/S'^^s) have
described species of Amia (Figs. 32,33) and of the some-
what related genus Lepidosteus, as well as teleosts like
Osteoglossiun, Pimelodiis, Asineops, Erismatopteriis, and
Diplomystiis that is allied to Cliipea and as such was des-
cribed by some authors. The English Mid-Eocene or Low-
er Bagshot series is variable in character and organic con-
tents, but, in its lower strata it includes the Alum Bay beds
that have yielded about 250 species of plants, largely
dicotyledonous; also the Bracklesham beds with marine
molluscs, elasmobranchs, and higher marine vertebrates.
Similar conditions are shown on the European continent,
except that there was a greater persistence of marine de-
posits. The most noteworthy of these marine beds are the
great nummulitic strata, which form the dominant mass
over central-east Europe.

The upper Eocene or Uinta formation, that may be
500-800 feet thick, is a direct continuation upward of the
Bridger and Wasatch below, and mainly differs in the new
species and genera that have evolved. In Europe the
formation again proclaims changing deposits of freshwater
and marine beds with their characteristic fossils.

The flora in all of these indicates a warm temperate
to a sub-tropical climate, though there may have been a
mixing of temperate region plants, washed down from
higher elevations, that commingled with others that grew
in warmer and lower ground. Thus species of Pinus,
Sequoia, Ginkgo^ Quercus, Nyssa, Magnolia and Liquidam-
bar, occur along with palms, Eugenia^ Eucalyptus, Laurus
and Ficus. Such a grouping is a sure indication that the
prevailing Triassic-Jurassic gymnospermic type of vegeta-
tion was being more and more replaced by an angiospermic
and mainly dicotyledonous type.

The invertebrates included a very rich and large series
of insects, numerous molluscs, also freshwater and marine
crustaceans. The freshwater fishes were now very largely
teleostean, but the ancient Jurassic group of the Amiidae
is represented by Amia and Pappichthys, the former of
which still survives in the North American species A. calva
(Figures 32, 33). Similarly the lepidosteans were abund-

From Eocene to Recent Time 235

ant, and have left remains from Wyoming eastward to
France and Germany; but they are represented only by a
few species in North America.

The teleostean fishes belonged to families that evolved
from more primitive "ganoid" freshwater groups like the
Semionotidae, the Pholidophoridae, and the Leptolepidae,
and which have all remained in a freshwater habitat till
now. Thus the Cyprinidae, the Siluridae, the Chromidae
and the Aphredoderidae are examples. Others like the
Clupeidae, Percidae, Atherinidae, and Serranidae are still
in part freshwater, but have largely migrated into the sea,
while still others of early Eocene origin branched off rapidly
and wholly into marine surroundings as did the Carangidae,
the Scombridae, and the Sparidae, that are treated of from
the standpoint of descent in a later chapter.

In addition to the above and other teleostean groups
like the Elopidae, the Albulidae, and the Chirocentridae,
that had already passed into the sea during Cretaceous
times, the sharks, dogfishes, and rays, as well as a few cest-
racionts must have been extremely abundant in individuals,
though dying out in species, when compared with Cretaceous
days.

Here we might again emphasize the evident relation
of fishes to bituminous production. Thus Leidy in speak-
ing of the Green River Shales, from which Cope described
several freshwater fishes, remarks that at "Petrified Fish
Cut" are thousands of beautiful fish remains, sometimes
a dozen or more appearing over a square foot. of rock.
Remains of insects and aquatic plants are also found in
these shales, and in one instance a feather of a bird. In
darker brown bands that are intercalated amongst others
of a greyish-buff color, the former "are saturated with a
bituminous matter which renders them combustible." The
source here then evidently was from death and decay of
enormous shoals of freshwater fishes. Similarly A. S.
Woodward and von Ihering have described a series of
Tertiary bituminous schists at Taubate in the province
of S. Paulo, Brazil (77^:63). These contain a great
wealth of fossilized freshwater teleostean fishes, belonging
to the Siluridae, Characinidae, Serranidae, and Chromidae,

236 Evolution and Distribution of Fishes

all of which are allied to genera still found in the fresh-
waters of South America. Von Ihering observes that these
schists crop out and are worked at several localities for
the crude petroleum oil. From the oil, supplies of gas,
paraffin, petroleum and sulphuric acid are obtained.

But in recent years, since many of the Eocene beds have
been examined from the economic standpoint, richly bitu-
minous rocks that seemingly owe their oils to decomposition
of marine fishes are now known. Thus in Texas and ad-
jacent states the rich oil beds that have been actively ex-
ploited during the past fifteen years, are also those which
contain an abundant and varied marine fish fauna that is
described in detail in another work. These belong to the
Cretaceous system, and seem in their faunal and strati-
graphic character to resemble other bituminous beds In
several parts of the world. Again the extensive Oligocene
and Miocene oil strata of western California owe their
oil-content, according to the present writers views, to the
marine fish fauna that has been only imperfectly described
as yet, but which Includes genera that belong to elasmo-
branch and teleostean families.*

The giant amphibians and reptiles of the two previous
epochs, had now almost disappeared, though smaller sala-
mandroid forms were left. Turtles, crocodiles, and snakes
were fairly common, as their entire skeletons or smaller
remains, testify. But the most noteworthy feature was
the appearance of representatives of all the great divisions
of the mammals, with the exception of the two highest.
The writer has elsewhere suggested (/ : 496) that these all
originated by modification and increase In size of various
more primitive marsupial ancestors. As with the giant
amphibians of the Permian, the giant reptiles of the Juras-
sic and Cretaceous, so with the giant mammals of the pres-
ent epoch; all of these furnish a rough and approximate
measure of the great amount of evolutionary advance that
some organisms may undergo, alongside others that vary
slowly.

*For detailed description of these see the author's volume, "Fishes the
Source of Petroleum."

From Eocene to Recent Time 237

But as Cope and Lesquereux emphasized, there seems
to have been a remarkable community both In organisms
and In physical phenomena, between Western Europe and
Western America during long periods of the Eocene, and
even on Into early Miocene time. Thus the latter, in com-
paring his results (z//: 127) with those of Saporta for
the g>'pses of AIx says: "Besides the general characters of
the Flora, the peculiar compounds of the formation, the
laminated shales mostly formed of ashes, the Immense
number of Insects and freshwater fishes preserved in a
succession of thin layers of greyish shale, are repeated in
the upper part of the gypses of AIx precisely as they are
found at Florissant." Says Saporta: "Entire shoals of
fishes were surprised and burled In the muddy clay of the
bottom. Even insects, suffocated In large numbers, from
the smallest kind of mosquitos to ants, bees, butterflies, are
preserved In the thin shales with the minutest of their
organs and even the color of their wings." Later he adds:
"The evidence of synchronism of the flora of Florissant
with that of the Ollgocene of France appears confirmed
by the characters of the fauna. At least Professor Cope
{i/S: 6'j) identifies the White River Group" in which are
the Florissant beds, "with the Aqultanlan and Tongrian
of Europe, — formations which close the Eocene, or are
partly referable to the Eocene partly to the Miocene, and
considers the Green River and the Wasatch as Suessonian
or Palaeocene. This agrees with the observations of
Saporta, who considers the gypses of Aix as a long series
of formations continuous through the different periods
Intervening between the Palaeocene and the Miocene,
the upper part even partaking of the character of this
last epoch." Cope's observations are equally apropos

A great part of the deposits thus referred to compose
the formation that is now known as Ollgocene, and which
connects upper Eocene with typical Miocene strata. But
the special interest is that a very close connection, and
even a direct continuity, in physical and biological pheno-
mena, Is thus set forth between Europe and Western
America. It confirms also the observations made above

238 Evolution and Distribution of Fishes

by the writer as to Amia, Pappichthys^ Lepidosteus, and
other fishes having been common to the lakes of the two
areas.

Accepting such wide general biological relations, certain
distributional features of Eocene fishes deserve attention
here. Thus according to all present knowledge the great
majority of the Cretaceous teleost genera had been oblite-
rated by the close of that period. Thus of 75 Cretaceous
genera recorded by Woodward {180) only one, namely
Dtplomystiis {Histiurus of Costa, Fig 34) passes from Cre-

FiG. 34. Diplomystus dentatus, a freshwater clupeoid fish from
Green River Eocene shales of Fossil, Wyoming. About one-fifth nat.
size. (After Veatch).

taceous to Eocene beds, 29 genera first appeared in the
Lower Eocene, 44 genera first appear in the Upper Eocene,
and almost wholly in the remarkable Monte Bolca deposits.
Now nearly all of the teleosts thus destroyed at the close of
the Cretaceous were marine types, derived from freshwater
"ganoids" during Jurassic and earlier Cretaceous times.
These belonged to the families Elopidae, Albulidae, Sauro-
dontidae, Chirocentridae, Ctenothrissidae, Clupeidae, Halo'-
sauridae, Notacanthidae, Dercetidae, Enchodontidae, Scope-
lidae, Gonorhynchidae, Chirothricidae, Muraenidae,
Crossognathidae, Berycidae, Stromateidae, Carangidae,
Scombridae, Percidae and Sparidae. Even a few only of
the great Cretaceous teleostean families were continued
into Eocene and later periods, not, so far as our knowledge

From Eocene to Recent Time 239

goes, In their ancient genera but only in evolved and de-
rivative genera from these that managed to persist. Thus
the Scopelidae are known to us by eight genera in the
Cretaceous, and they seem thereafter to have become large-
ly decimated or modified, to reappear only in the Oligocene
and Miocene strata of Switzerland and Northern Italy
as the genera Scopeloides^ Parascopelus and Anapterus.
The Berycidae show six Cretaceous genera — for Beryx
seems to be wrongly credited to the Cretaceous — which then
become largely blotted out, to reappear as MyripHstis and
Holocent7-iim of the Upper Eocene.

In contrast to the above, the elasmobranch fishes that
passed from freshwaters into the sea during Jurassic and
Cretaceous times, are represented by fifteen genera, which
have persisted at least from the latter period on through
the Eocene to the present day. These are Acanthias, Cen-
trophonis, Squatina, Rhinobatus,, Raja, Cyclohatis, Noti-
damis, Cestracion, ScyUiiim, Pristiurus, Scapanorliynchus,
Odontaspis^ Oxyrhina, Ginglymostoma, and Larnna. Vari-
ous reasons might be given for such differences in relative
persistence.

In addition to marked deformations by volcanic agency
at the beginning of the Eocene period, ample proof exists
of continued volcanic action during deposition of these
beds In many countries.

But toward the close of the Eocene and in early Oligo-
cene time, some phenomenal displays of earth-movement
and volcanic activity took place, which would largely ex-
plain the profound changes witnessed in the animal life,
and not least in the fish life of those days, as compared with
the late Oligocene and Miocene periods. Thus a large
part of South Europe, North Africa, South Central Asia
on to Japan, the Philippines and Sumatra at least, formed
a great and continuous sea during Eocene time, and which
is approximately outlined in the chart (Fig. 35).

In this sea the huge foraminifer Niimmulites became
the prevailing marine organism, while in part by accumula-
tion of calcareous nummulitic tests, In part by activity of
calcareous bacteria, deposits were formed that range from
100 to 3,000 feet in thickness. At this time the Pyrenees,

240 Evolution and Distribution of Fishes

From Eocene to Recent Time 241

Apennines, Alps, Carpathians, Himalayas, and minor
mountain ranges between, were as yet incompletely elevated
or were still submerged areas.

But from late Eocene to early Oligocene time diastrophic
activity caused increasingly enormous elevation of this area
in some centres, and corresponding depression in others to
form the Mediterranean, Red Sea, or Persian Gulf. These
changes gave rise to great faults, and caused pronounced
volcanic activity, largely probably from frictional heating
and melting of subterranean or submarine strata, over the
areas affected. Such culminated in at least four important
results: (i) The above-named mountain-masses became
elevated high above sea-level as huge ridges of land from
8,000 feet to 16,000 feet at least high, over the sides, or
even as in the Alps over the tops, of which the nummulitic
beds were upraised. (2) Extensive outflows in part of
subaerial, in part of submarine volcanic tuffs, diabases, and
related rocks took place from Italy eastward to Tasmania,
also over at least Western America. This must have caused
sudden and widespread death of both marine and fresh
water fishes, as well as great deposits of volcanic dust beds,
such as Russell has traced. (3) The nummulitic organisms
suffered so severely that they soon dwindled in importance,
and largely disappeared toward the close of the Oligocene.
(4) Many species and even genera of fishes suffered ex-
tinction, and when heaped in masses over many hundreds
of miles, gave rise in time to those rich accumulations of
petroleum shales and sandstones, whose existence and
wealth are only now being made known in all their fullness.
As compared with statistics already given for Cretace-
ous and early Eocene days, it might be added that of known
Eocene genera still living there are 60, of which nearly
all of the most primitive are and have been freshwater, or
have only in part passed into the sea. Of these latter there
are 25. The remaining 35 genera include freshwater forms
and a greater or less number of more specialized marine
types in nearly every case. Not a few of them frequent
the coast lines at the present day; only the larger, more
powerful, or most highly modified genera like the tunny,
cod, conger eels, etc., being oceanic or deep-sea.

242 Evolution and Distribution of Fishes

If we think only however of the recorded telecst fishes
of the Eocene period about 52 are freshwater genera in
whole or in part, while 47 are purely marine. It follows
from what has been said that there is clear evidence of
two successive teleostean developments and progressions
from a primitive freshwater to a marine environment.
First, from freshwater ganoid ancestors belonging to the
groups Pachycormidae, Aspidorhynchidae, Pholidophori-
dae and Leptolepidae originated the late Jurassic or Cre-
taceous families Saurodontidae, Holosauridae, Enchodon-
tidae, and others already cited. These were suddenly and
very extensively obliterated by the close of the Cretaceous,
largely owing, as we would consider, to the world-wide
effects of a tremendous volcanic activity in most of the conti-
nental centres. Second, in part from evolving genera of the
above groups that escaped destruction, in large part how-
ever by a later and new migration from freshwaters by
members of the Clupeidae, Aphredoderidae, Berycidae,
Percidae and others during Eocene days, the progenitors
of our existing and abundant marine teleost fauna were
established. Details of all of the above are elaborated
later on (p.p. 357, 373).

II. Oligocene-Miocene Formation. As already ac-
cepted by Saporta, Cope, Lesquereux and more recent
authors, complete conformability of strata, and continuity
of organismal types can be traced from the Upper Eocene
to the lower Oligocene and up into Miocene strata in some
areas alike of the Old and New World. But a distinct
break and unconformability is observed in other regions.
Further, frequent elevations and depressions of land-levels
took place, so that freshwater, marine, and even eolian
land deposits were laid down. Steady evolution of new
genera and families of plants and animals, as well as elimi-
nation of older types proceeded rapidly. All of the im-
portant groups of animals had now appeared except the
genus Homo, so far as we know.

Separation of the land-masses into such as now exist had
almost completely been effected by end of the period. Ex-
plain it as we may also, the flora in wide regions of the
Northern Hemisphere took on a semi-tropical aspect, and

From Eocene to Recent Time

243

a warm-temperate climate existed even in Greenland. Such,
succeeded by colder conditions, would stimulate to organ-
ismal modification and evolution. Extensive rivers and
lakes existed in north, in central, and in south Europe, in
Africa, where Tanganyika was a persistent feature from
late Cretaceous times probably (p. 482) ; in North America
where thick lacustrine and eolian deposits — interspersed
at times by heavy deposits of volcanic dust and ash — gave
rise to the White River Formation.

One of the most extensive and informing deposits of
Lower Oligocene age in Europe, is the Tongrian or Upper
Flysch series of marine rocks, that can be traced from East
France, the Voges, Glarus, N. Italy, and Vienna northward
through Bavarian, Swabian and Danubian territory to
Moravia and Galicia on the east. Much if not all of this
region was a marine expanse, over which deposits were
made to a depth of from 1000 to 6000 feet, and while as
yet the greater part of the Alps was not in existence. But
simultaneous with these deposits, according to the writings
of Heer, extensive lakes and swamps in central and north
Germany were accumulating freshwater deposits which
closely resembled those described below for Switzerland.

The above marine rocks, as studied by Hauer {181:
104), Suess (7^2:87), Paul, and Fuchs amongst others,
are divisible into a lower and upper zone. The former
is known as the "amphisyle" zone, for the most conspicuous

Fig. 36. Amphisyle heinrichi. A specially abundant and highly
modified fish of the marine Oligocene rocks from Alsace to Baku.
Enlarged nearly twice nat. size. (After Heckel).

Fig. 37. Amphisyle scutata, an East Indian marine fish of
near affinity with the above, but somewhat larger. (After Day).

244 Evolution and Distribution of Fishes

organism is a centriscid teleost Amphisyle heinrichi (Fig.
26), the remains of which are "crowded beside and over
each other." It is nearly related to the living A. scutata of
East Indian waters, that is shown in Figure 37. Close
on 20 other teleosts have also been recognized. This
enormous abundance of teleostean fishes, according to the
writer's view, would explain the dark color and rich bitu-
minous material of extensive strata that can be traced for
hundreds of miles along the Alps and Carpathians into
West Asia. Several species of the above genus still exist
in the tropical seas of the Old World. Alongside these
were Meletta crenata and several species of the scombrid
Lepidopus, a genus whose species are still met with in many
seas, also other and less abundant teleosts.

The upper zone or "Menilite" shales proper are chiefly
characterized by the abundance of the clupeoid genus
Meletta, the crowded remains of which as well as other
teleosts, give a highly bituminous character to the rocks.
It is worth noting that Meletta {Cliipea) sardinites
(Figs. 38, 39) of these rocks is a near ally of the common
herring, sardine, anchovy and sprat, the oil content of
which is well known. Suess strongly suspected (op. cit.
p. 146) that the rich fish remains and the bituminous con-
stitutents of these rocks were related to each other.

Fig. 38. Meletta {Clupea) sardinites. An abundant and typi-
cal marine teleost from the menilite shales of Mid Europe.

Fig. 39. Skeletal restoration of the same fish. (After Heckel).

From Eocene to Recent Time 245

That active land denudation and resedimentation were
frequent is shown by some lacustrine deposits of the period
that vary from 2000 to 12,000 feet In thickness. These
lacustrine deposits evidently originated in many cases from
temporary elevation of marine areas, and conversion of
these into lakes which received the waters of rivers, and
became quickly stocked with a freshwater fauna. Varied
glimpses are furnished from several of the continents, of
the biological conditions that then existed around such
lacustrine areas. Thus in O. Heer's striking work, as
translated by Heywood (/^j), the following classification
of the rocks that are known as "the Molasse" is given,
along with their leading organic contents. This applies
to the so-called Oeningen flora and fauna that are amongst
the richest known;

Miocene, (i) Oeningian or Tortonian. Upper fresh-
water Molasse and brown coal.

(2) Helvetian or St. Gallen Molasse. Marine beds
with animals in part of Mediterranean, in part of tropical
fades.

(3) Lhangian or Mayencian. Lower freshwater or
grey molasse but with intercalated marine beds.

Oligocene (i) Aquitanian. Red Molasse or lower
brown coal, with lignite seams and abundant terrestrial
vegetation. 1000 m. thick in Italy,

(2) Stampian. In Italy 600 m. thick.

(3) Tongrian or Lower marine Molasse. Shells, num-
mulites etc. 2000 m. thick.

(4) Sestian, a marine Italian series, about 20 metres
thick.

Regarding the freshwater molluscs Heer remarks:
"All the univalve MoUusca which Inhabited the Swiss
Miocene forests, and the bivalves which peopled the brooks
and lakes, belong to living genera. The species however
are almost entirely extinct; and their nearest allies are no
longer inhabitants of Switzerland." Snails were very
numerous, and include Pupa, Planorhis, Limnaea, Palti-
dina and Melania. As to the species Melania escheri he
notes that its nearest living allies are In the rivers of tropical
Asia. Numerous arachnids, also 844 species of insects that

246 Evolution and Distribution of Fishes

included 543 beetles, 20 Orthoptera, 29 Neuroptera, 81
Hymenoptera, 3 Lepidoptera, 64 Diptera and 136 Hemip-
tera are all recorded.

At Oenlngen, which is situated on the north or Baden
side of a narrow arm of Lake Constance, occur two lime-
stone quarries at a height of 550 feet and 700 feet above
the level of the lake. Of one Heer says: "In the lower
quarry, immediately upon the yellow marl, there is an
extremely fine-grained limestone, which Is only one inch
In thickness, and splits into yellowish or grey layers as thin
as paper. In these layers the plants and insects are em-
bedded, and often are so wonderfully well preserved that
they look as if they had been painted."

The fossil fishes "occur both in the upper and the lower
quarry, but are restricted to particular beds. Up to the
present 32 species have been described, belonging to 15
genera. Of these genera only one [Cycliirus) allied to the
carps, but distinguished by its rounded caudal fin is extinct;
all the others are still met with living In freshwaters." As
to their distribution, then and now, he makes the following
suggestive observations: of the genera "which Oenlngen
has In common with the existing fauna, only one, the Cottus,
belongs exclusively to the temperate and cold regions; all
the rest occurring also In Mediterranean countries, or even
in tropical and sub-tropical zones. The genera Perca,
AcanthopsiSy Cobites, Gohio, Leuciscus and Asphis are also
represented in Indian rivers, and eels are found in Madeira
and Teneriffe. To this must be added that the fish-fauna
of Oenlngen contains a number of species usually belonging
to genera of warmer lands. The genus Lehias, represented
by four small species, now Inhabits Italy, the East, and
America. Poecilia occurs only In the swamps of Carolina
and South America, and Cychiriis Is extinct. Thus side by
side with those genera which still occur In Switzerland, but
the greater part of which extend their range Into warm and
even torrid zones, other fishes are found which now ex-
clusively belong to hot countries."

Further on he says: "The fishes of Oenlngen belong to
six families. The richest in species Is that of the Carps
(Cyprinoidei) which Includes 21 species. Five of these

From Eocene to Recent Time 247

belong to the genus Leuciscus This genus was al-
ready widely diffused in Miocene times, and it is at present
to be met with in the rivers and lakes of all parts of the
world."

A highly suggestive feature in some of the strata is the
apparently seasonal succession of the deposited material,
alike inorganic and organic. Thus it is said: "The insect-
bed consists of about 250 lamellae or layers, the formation
of which probably occupied a long series of years, during
which plants and animals were deposited at all seasons
of the year in this book of nature. The layers that contain
the flowers of the camphor trees and poplars were probably
produced in the spring time, those which furnish winged
ants and the fruits of elms, poplars, and willows in the
summer, and those containing the fruits of the Camphor
trees, the Diospyros, the Clematis, and the Synantheriae
in the autumn. The deposits must have been formed in
quiet water, and at a distance from the mouth of any river.
Probably poisonous gases or vapors rose from this spot
into the air, and killed the insects flying over the water.
The prodigious number of species of insects here met with
shows us that not only the animals of the neighboring
shores, but those of a large area, must in the lapse of time
have here found their graves."

Of the rocks and their contents belonging to the upper
quarry he says: "The compact indigo-blue marl which
covered the bottom of the lake, is overlaid by a hard bitumi-
nous limestone, which has received the name of Kettlestone.
It is the chief source of the fossil plants of Oeningen." This
Kettlestone also contained land and freshwater insects and
crustaceans, while higher up he says it is covered by a thick
white bed with large pike, a gigantic frog, a tortoise, and
a large salamander. He considers that the ground then
became dry, and later was submerged, when a deposit of
four feet of a hard limestone ("mocken,") was formed
in which were tench, other fishes, and aquatic plants. Next
"a period of perfectly still water succeeded, in which a
great quantity of larvae of dragon flies swam about." From
the fact also "that dragon fly larvae of all ages lie inter-
twined in certain slabs, it would appear that these insects

248 Evolution and Distribution of Fishes

had been suddenly killed, and that they were subsequently
enveloped by snow-white limestone. Had there been no
violent action it would be difficult to explain how such quanti-
ties of these larvae could have been buried in the rock, some
in a running, others in a resting position, with the mask,
extended or retracted." In the next higher bed the dragon-
flies disappear, but numerous remains of the white-fish
Leuciscus are now found.

Heer then considers that "a rising and sinking of the
ground," which might be due to volcanic agency, probably
took place, since a volcanic rock occurs "that resembles
the phonolitic and basaltic tuffs of the neighboring Hohgau.
Further "it is manifest that the volcanoes of the Hohgau
were in activity at the same time with those of Oeningen."

While agreeing with much of the valuable and original
information contained in these volumes, not least that
quoted above, the writer nevertheless would give a different
interpretation to some of the phenomena presented. As
to the origin of much of the richly fossiliferous rock-
substance, and specially the numerous thin lamellae noted,
he would regard such as intermittently successive deposits
of volcanic lime-dust laid down in the course at most of
a few years. The source of this dust Heer sufficiently
accounts for in his mention of the not far-distant volcanoes.
In conjunction with this we must bear in mind that huge
thicknesses of limestone strata were on every side and had
to be broken through, caught up periodically in the volcanic
vents, and ground to powder there before being extruded
(p. 44) as a