Samuel Wendell Williston.

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or nearly all of the original skeleton has been preserved together
in its natural relations. After days, perhaps weeks, of labor, the
specimen is secured and shipped to the laboratory. Those parts
which have been washed out of the chalky rock before the dis-
covery of the specimen are always more or less injured and for the
most part lost, their fragments strewn down the hillside, for erosion
is always slow and many years may have elapsed since first the
specimen had appeared at the surface. More frequently, perhaps,
a few strokes of the pick and shovel disclose but one, two, or three
bones remaining in the rocks. The specimen, if large, or composed
of many bones, is carefully uncovered sufficiently to show its extent,
and then, so far as possible, removed in large blocks of the rock.
The bones themselves, notwithstanding their petrifaction, are
usually soft and easily broken, and their separate removal from the
matrix may require weeks or even months of labor, work which
cannot be done prudently in the field.

Of many specimens the rock matrix is so hard that the task of
removing it from the bones is slow and difficult, indeed well-nigh
impossible, for the bones are usually softer than their surrounding
matrix. On the other hand, the matrix may be so soft and friable
that it cannot be quarried out in blocks. In such cases the separate
divisions, as large as they can be excavated and safely handled,
are carefully covered with thick bandages of burlap and plaster-of-
paris, often strengthened with rods of iron or boards. The skeleton
of a single animal treated in this way may require weeks and even
months to collect, prepare, and mount in the museum.

From what has been said the reader will understand how it is
possible to make an approximately accurate picture of extinct
animals as they appeared in life — approximately accurate, never
absolutely so. The flesh and other soft parts of an animal are
never petrified, though it is a common belief that they may be.
Petrified men and women are still occasionally shown in cheap
museums, but they are always frauds. Many times has the writer
been called upon to express an opinion as to the nature of seme con-
cretion which the discoverer was sure was a petrified snake, turtle,



INTRODUCTION



II



or even some part of the human body, because of fancied resem-
blances in shape and size. Not too emphatically can it be said
that anything dug. from the earth having the shape of a living ani-
mal and alleged to be petrified is either an accidental resemblance
or a deliberate humbug — if we except such extraordinary casts as
those of Pompeii. The Cardiff Giant and the Muldoon are still
fresh in the memory of some of us. There have been a few instances
where flesh has been preserved in the North, frozen for thousands




Fig. 2. — Removing a specimen of fish in a block from the chalk of western Kansas



of years, but frozen fossils are very different from petrified fossils.
Flesh decays before it possibly can be petrified, and only rarely
is the residue of flesh, tendons, and skin, that is, the carbon and
mineral matters, preserved.

One may sometimes restore extinct animals as in life, knowing
fully the shape and structure of the skeleton, and still be far from
the real truth. All elephants. of the present time have a bare or
nearly bare skin. If all that we knew of the extinct mammoth
were derived from the skeleton we should never have suspected



12 WATER REPTILES OF THE PAST AND PRESENT

that the creature was clothed during life with long and abundant
hair, such as has been found with the frozen bodies in Siberia.
Nor should we suspect that the dromedary and Bactrian camels of
today have large masses of fat on their backs, if we knew only their
skeletons. It must therefore be remembered that all restorations
of extinct animals, representing them as in life, are merely the sum
of our knowledge concerning them, as close approximations to the
real truth as it is possible to make. Or, rather, they should be
such approximations; unfortunately many such restorations have
been made by artists wholly unacquainted with the anatomy of the
creatures they attempt to represent, often adorned with appendages
drawn from a too vivid imagination.



CHAPTER II
CLASSIFICATION OF REPTILES

There is very much doubt, very much uncertainty, among
paleontologists about the classification of reptiles. No two writers
agree on the number of orders, or the rank of many forms. Some
recognize twenty or more orders, others but eight or nine. And
this doubt and uncertainty are due chiefly to the many discoveries
of early forms that have been made during the past twenty
years. The many strange and unclassifiable types which have
come to light in North America, South Africa, and Europe have
thrown doubt on all previous classificatory schemes, have weakened
our faith in all attempts to trace out the genealogies of the reptil-
ian orders; and classification is merely genealogy. It is only the
paleontologist who is competent to express opinions concerning the
larger principles of classification of organisms, and especially of
the classification of reptiles. The neozoologist, ignorant of extinct
forms, can only hazard guesses and conjectures as to the relation-
ships of the larger groups, for he has only the specialized or decadent
remnants of past faunas upon which to base his opinions. About
some things we can be quite confident; about some groups opin-
ions have crystallized, and we all agree, except perhaps on trifles.
The dinosaurs, the pterodactyls, the crocodiles, for instance, offer
only minor problems to perplex the systematist, but the origin
and the relations, not only of these, but also of nearly all the others,
are still involved in obscurity. The question, whence came the
ichthyosaurs, the plesiosaurs, the turtles, etc., seems almost as far
from solution as it did fifty years ago. With every problem solved
a dozen more intrude themselves upon us. Hence, classification
simply represents the present condition of our knowledge, our
present opinions as to genealogies. It was the fashion a dozen
years ago to draw all sorts of genealogical trees on the slightest
pretext, to trace in beautifully clear lines the precise descent of all
kinds of animals; and very few have been worth the paper on

13



14 WATER REPTILES OF THE PAST AND PRESENT

which they were printed. When facts are numerous enough, con-
clusions are patent even to the novice; when facts are few and
obscure, one can guess about as well as another. In general, it may
be said that the older a group of animals is the more abstruse are
the problems presented; first, because of the lack of abundant
material; second, because the forms speak to us in an unfamiliar
language that we cannot easily interpret. The classification of the
mammals approaches more nearly the ultimate truth than does that
of any other group of organisms, because we know more about the
extinct forms than we do of any other class, and also because we
know more about the living forms than we do about any other
living animals.

Species of reptiles are, for the most part, vague quantities in
paleontology; they can be determined with assurance only by the
comparison of abundant material. Adult characters in mammals
are apparent in the ossification of the skeleton, and size can be used
within moderate limits in the determination of species; but size
in reptiles means but little; no one could possibly say that the
skeleton of an alligator six feet in length is not that of an adult
animal if he knew nothing else about the Crocodilia. So also the
compression and malformations of bones from the processes of
fossilization obliterate specific characters in great part. Nor are
specific characters easily distinguishable in the skeletons of living
reptiles. The genus, therefore, among fossil reptiles is practically
the unit, and we may be sure that for every well-defined genus we
discover there existed numerous minor variations, which, had we
the living animals to study, we should call species. We classify
the living Crocodilia into two families, about four well-defined
genera — perhaps even five or six — and about twenty-five species.
Of the living lizards there are about eighteen hundred species,
twenty families, and four larger groups or suborders. In all
probability the lizards have never been more abundant and more
varied than they are at the present time. Possibly these propor-
tions of species, genera, families, and suborders may represent
approximately the proportions that have existed at some time or
other in most of the other groups which we call orders — approxi-
mately only, for we can never be quite sure that we evaluate the



CLA SSIFICA TION OF REPTILES 1 5

structural characters of different groups of organisms quite equally.
The absence of a molar tooth in a mammal would ordinarily indicate
a genus, the absence of a tooth in a reptile might not indicate even a
variety or a race. Whence it follows that classification of organ-
isms is not and never will be an exact science. The value of char-
acters used in classification is very unequal, as we have seen. No
two persons see these characters from the same viewpoints, and in
consequence no two persons whose opinions are worth while ever
wholly agree as to classification.

The following scheme differs only in minor details from the
more conservative of the generally accepted views, and those
differences are, for the most part, the writer's own opinions, to be
taken for what they are worth. It may be said decisively that
no classification of the reptiles into major groups, into super-
families or subclasses that has so far been proposed is worthy of
acceptance; there is no such subclass as the Diapsida or Synapsida,
for instance. And we have very much more to learn about the
early reptiles before any general classification of the reptiles can be
securely founded. It is very probable that the primary radiation of
the reptiles into the various lines of descent, into its main branches,
occurred much earlier than we have been disposed to believe; that
before the close of Paleozoic time, perhaps before the close of the
Carboniferous, all the great groups of reptiles had gone off from the
main stem, and that since then only smaller and smaller branches
have appeared. There have been no new orders of reptiles in all
probability since Triassic times, and perhaps none since Permian.

Taxonomists are often disposed to cut the Gordian knots of
relationships by raising the ranks of the animals they study to
independent positions. More than thirty independent orders of
reptiles have been proposed by different students, and quite as
many of mammals and of birds; possibly after more forms have
been discovered there will be as many proposed for the amphibians.
Sometimes, indeed, it is better to make such independent groups
than to unite lesser ones on doubtful evidence. But the writer,
for one, believes that it is more worthy of the thoughtful scientific
student to seek for relationships than for differences. It is far
easier to destroy than to construct, to make new genera, families,



16 WATER REPTILES OF THE PAST AND PRESENT

and orders than to unite those already proposed. To raise every
proposed suborder of reptiles to an order, as has been proposed
by various writers, and the orders to subclasses, only leaves classi-
fication where it was; nothing has been added to taxonomy save
a lot of new names to perplex and annoy the student.

In the following scheme of classification three groups provision-
ally called orders are prefixed by an asterisk.

CLASS REPTILIA

. Order COTYLOSAURIA

Primitive reptiles with notochordal vertebrae, imperforate temporal region,
persistent intercentra; two coracoids; plate-like pelvis, with all or most
of the amphibian skull elements; short legs and short neck; phalangeal
formula primarily 2, 3, 4, 5, 3(4).
Suborder Diadectosauria Permocarboniferous, North America.

Pantylosauria Permocarboniferous, North America.

Labidosauria Lower Permian, North America.

Pareiasauria Upper Permian, Europe, Africa.

Procolophonia Triassic, Europe, Africa.

Order CHELONIA

Temporal region imperforate. Head and limbs more or less retractile
within a box formed chiefly by the exoskeleton.
Suborder Pleurodira Triassic to recent.

Cryptodira Jurassic to recent.

Trionychoidea Cretaceous to recent.

Order THEROMORPHA

Primitive reptiles with notochordal vertebrae, perforate temporal region,
persistent intercentra; two coracoids; plate-like pelvis with median vacu-
ity; no free dermosupraoccipitals in skull ; longer legs and neck; phalangeal
formula 2, 3, 4, 5, 3(4).

Suborder Pelycosauria (sens, lat.) Permocarboniferous, North America,

Europe.
Dromasauria Upper Permian, Africa.

Dinocephalia Middle and Upper Permian, Africa.

Order THERAPSIDA

Reptiles with a single temporal perforation on each side; vertebrae not
notochordal; intercentra not persistent; pelvis with vacuity; skull bones
reduced; teeth heterodont; phalangeal formula, 2, 3, 3, 3, 3.
Suborder Anomodontia Permo-Trias, Africa, North America.

Therocephalia Upper Permian, Africa.

Theriodontia Trias, Africa.



CLASSIFICATION OF REPTILES 17

Order SAUROPTERYGIA

Aquatic reptiles with a single temporal vacuity; no supratemporal bone,
or quadratojugal; ribs single-headed, diapophysial ; coracoids large, meet-
ing in middle line, single; neck long, tail short.

Suborder Nothosauria Triassic, Europe.

Plesiosauria Triassic to close of Cretaceous, cosmopolitan.

*Order PROGANOSAURIA

Primitive aquatic reptiles; single (? upper) temporal perforation; neck
elongate; nares posterior; vertebrae notochordal; intercentra persistent;
pelvis plate-like; phalangeal formula 2, 3, 4, 5, 4(6). Permocarboniferous,
. Africa, South America.

Order ICHTHYOSAURIA

Reptiles with all aquatic adaptations; a single, upper temporal perfora-
tion; both supratemporal and squamosal present; a single coracoid.
Middle Triassic to Benton Cretaceous, cosmopolitan.

*Order PROTOROSAURIA

A single, upper temporal vacuity, quadrate fixed (neck vertebrae elongate) ;
bones hollow; cervical ribs single-headed, articulating with centrum;
pelvis plate-like. Permian, North America, Europe.

Order SQUAMATA

A single, upper temporal vacuity, or, secondarily none; quadrate loosely
articulated with cranium; teeth on palate; intercentra more or less per-
sistent; a single coracoid; ribs single-headed, central.

Suborder Lacertilia Trias to recent.

Mosasauria Upper Cretaceous, cosmopolitan.
Ophidia Upper Cretaceous to recent.

*Order THALATTOSAURIA

Aquatic reptiles; two (?) temporal vacuities; ribs single-headed, attached
to centrum; single coracoid; no intercentra. Trias, California.

Order RHYNCHOCEPHALIA

Two temporal vacuities on each side; palate with teeth; intercentra
persistent; a single coracoid; teeth acrodont; ribs articulating with
centrum and arch.

Suborder Rhynchosauria Triassic, Europe.
Sphenodontia Triassic to recent.

Choristodera Uppermost Cretaceous, lowermost Eocene,
North America, Europe.



18 WATER REPTILES OF THE PAST AND PRESENT

Order PARASUCHIA

Subaquatic reptiles, with two temporal vacuities; an antorbital vacuity;

no false palate; pubis entering acetabulum; ribs double-headed, diapo-

physial.

Suborder Phytosauria Upper Trias, cosmopolitan.

Pelycosimia Trias, Africa.

Pseudosuchia Trias, Europe, North America.

Order CROCODILIA

Two temporal vacuities; teeth thecodont; a false palate; pubis excluded
from acetabulum; single coracoid; ribs double-headed, diapophysial;
subaquatic or aquatic.
Suborder Eusuchia Jurassic to recent.

Thalattosuchia Upper Jurassic, Europe.

Order DINOSAURIA

Ambulatory reptiles, with two temporal vacuities; no false palate; pubis

entering acetabulum; ribs double-headed, diapophysial.

Suborder Theropoda Upper Trias to close of Cretaceous, cosmopolitan.

Orthopoda Close of Trias to close of Cretaceous, cosmopolitan.

Sauropoda Upper Jurassic, Lower Cretaceous, cosmopolitan.

Order PTEROSAURIA

Volant reptiles; fourth finger greatly elongated to support patagium;
neck vertebrae elongated; bones hollow; ribs double-headed, diapo-
physial; a single coracoid; no clavicles or interclavicle ; two temporal
vacuities.
Suborder Pterodermata Jurassic, Europe.

Pterodactyloidea Upper Jurassic to Upper Cretaceous, Europe,
North America.



CHAPTER III
THE SKELETON OF REPTILES

The bony framework, or skeleton, that which gives form and
stature to the body, and which serves for the support of the soft
parts and the attachment of muscles, is, with rare exceptions, all
that is ever preserved of fossil animals. Because, therefore,
students of extinct animals must rely so much, if not exclusively,
upon the skeleton much attention has been given to the study of
comparative osteology, the science of bones. Not only are most
of the bones of the skeleton characteristic of the genus to which
they belong, but the more general plan of the skeleton, or parts
of the skeleton, is likewise characteristic of the larger groups. The
paleontologist may become so expert in deciphering the characters
of single bones, or even parts of bones— often all that are known
of animals new to science — that he is able to hazard guesses as to
the general structure of the skeleton to which they belong. But
such guesses usually will approximate the real truth only in the
degree that the bones upon which they are based approximate
like bones of other animals that are better known. Not all parts
of the skeleton are equally characteristic of the type of animal which
possessed them. A tooth of a mammal may positively determine
the species to which it belongs, while the toe bone of the same
animal might not enable one to guess at its family, even. As a
rule one can seldom be quite sure of the species of a reptile unless
the larger part of the skeleton, or at least the skull, is available,
although almost any bone of the skeleton, if one is expert, will
permit a decision as to the family, if not the genus.

One must often depend upon the positions and relations of the
bones, as found in the rocky matrix, for the final determination
of many characters. One can, for instance, never be sure of the
number of bones in the neck, trunk, tail, or feet of a reptile, until
specimens have been found with all such bones in position. It
is for this reason that much care is exercised in the collection of

19



20



WATER REPTILES OF THE PAST AND PRESENT



PL|



specimens of fossil animals, and especially
of fossil reptiles, to preserve all parts of
the skeleton, so far as possible, in the
relations they occupied in the rocks until
they can be studied in the laboratory.
Many grievous errors have been made in
the past by hasty inferences from fragmen-
tary and poorly collected specimens.

Because of the reliance which must be
placed upon the skeleton it will be neces-
sary to speak somewhat in detail of its
structure in the reptiles, and to use not
a few terms in its description that are
unfamiliar to the general reader. So far as
possible technical terms will be avoided,
though some must be used, as there are
no equivalents in the English language
for them. The reader may use this
chapter as a sort of explanatory index
or glossary for the better elucidation of
the necessary details of the following
chapters.

It is needless to say that the skeleton of
a reptile is arranged on essentially the
same plan as that of our own; the bones
have the same names that they have in
our own skeleton, but there are more of
them, and the individual bones, as a
general rule, are less highly specialized,
that is, are not so well adapted for special
functions. In a word, the skeleton of a
reptile for the mcst part is generalized,
though particular parts may be highly
specialized for particular uses. As a rule,
if not as a law, the course of evolution
has been to reduce the number of parts
and to adapt those which remain more



THE SKELETON OF REPTILES



21



closely to their special uses, either by increase in size, or by modifi-
cations of their shape and structure.

SKULL AND TEETH

The skull of reptiles is much more primitive or generalized in
structure than is that of mammals, to such an extent, indeed, that
there is yet much doubt as to the precise homologies of some of the
bones composing it; and, inasmuch as the names were originally
given, for the most part, to the bones of the human skull, there is
still some confusion among students as to the proper names in

all cases, a confusion that doubt-
less will not be wholly dissipated
until we know much more about
the early or more primitive
reptiles than we do at present.





Fig. 4



Fig. s



Fig. 4. — Seymouria, a primitive cotylosaurian. Skull, from above: pm, pre-
maxilla; n, nasal; /, lacrimal; p, prefrontal; /, frontal; pf, postfrontal; it, inter-
temporal; st, supratemporal; sq, squamosal; ds, dermosupraoccipital; t, tabulare;
j, jugal; po, postorbital; m, maxilla; s, surangular; ang, angular; pa, parietal.

Fig. 5. — -Seymouria, skull from the side. Explanations as in fig. 4.

As in other parts of the skeleton, there has been a reduction
in the number of parts of the reptile skull from that of the more
primitive forms, and a better adaptation of those which remain
for the special uses they subserve. This reduction in number has
been caused in part by the actual loss of bones, in part by the fusion
of contiguous ones. The most primitive reptiles had no less than
seventy-two separate bones in the skull; 1 the human skull has

1 Paired maxillae, premaxillae, nasals, prefrontals, lacrimals, frontals, parietals,
dermosupraoccipitals, tabularia, supratemporals, intertemporals, squamosals, jugals,
quadratojugals, postorbitals, postfrontals, quadrates, exoccipitals, paroccipitals,
vomers, palatines, pterygoids, sphenomaxillae, stapes, transverse, alisphenoids or
orbitosphenoids, epipterygoids, articulars, prearticulars, angulars, surangulars, coro-
noids, splenials, dentaries, one supraoccipital, one basioccipital, one basisphenoid,
one ethmoid.



22



WATER REPTILES OF THE PAST AND PRESENT



but twenty-eight inclusive of the ear bones. There is but little
variation, either in the number or in the relations of bones, in the
mammalian skull. If one knows the human skull thoroughly he
can easily understand the structure of the skull of any mammal.
The same cannot be said of the skulls of reptiles; one would be
greatly puzzled in the comparison of the skulls of turtles and croco-
diles, if he knew nothing about other forms. And it is safe to
formulate another general law in evolution here : Characters which

have been longest inherited are
least liable to change. The earliest
reptiles had at least four pairs of
bones which have disappeared in
all later reptiles; and they had
some bones in pairs which have
fused in later reptiles, either with
their mates or with contiguous
bones. The crocodile has at least
two pairs of bones which have
disappeared in turtles. On the
other hand, the turtle has at least
one pair of free bones which have
been fused with adjacent bones in
the crocodiles, and one pair that
is fused which is free in the latter.
The lizard has one pair of bones
that has been wholly wanting in
other reptiles for millions of years,
while on the other hand it has lost
some bones that are present in all other modern reptiles. The
four parts of the occipital bone of mammals, basioccipital, exoccipi-
tals, and supraoccipital, are almost invariably free and there is a
single occipital condyle, except in the Theriodontia.

In this reduction or fusion of parts, or in addition thereto, there
has been a general lightening-up of the whole skull-structure in
reptiles from the rather massive and protected form of the older
to the lighter, less protected, and more fragile type of the
later ones, since speed, greater agility, better sense organs, and




Fig. 6. — Labidosaurus , a cotylosaur.
Skull from above: pm, premaxilla; n,
nasal; m, maxilla; /, lacrimal; p, pre-
frontal; fr, frontal; pf, postfrontal;
po, postorbital; j, jiigal; pa, parietal;
sq, squamosal; ds, dermosupraoccipi-
tal; pf, parietal foramen.



THE SKELETON OF REPTILES



23



doubtless greater brain power have rendered unnecessary or useless
trie older kinds, just as modern methods and modern arms have
rendered useless the coat of mail of the Middle Ages.

The old reptiles had a continuous covering or roof for the skull ,
pierced only by the openings for the nostrils in front — the nares —


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Online LibrarySamuel Wendell WillistonWater reptiles of the past and present → online text (page 2 of 19)