RHYNCHOCEPHALIA
In some of the small islands near the northeast coast of New Zealand
certain small and peculiar, lizard-like reptiles, known as tuateras,
have long been known. For many years they were supposed, even by
scientific men, to be real lizards, so much do they resemble in
external appearances and in habits the lizards of other parts of the
earth. It was early observed, however, that they presented certain
remarkable internal differences from the real lizards or Lacertilia,
though it was not till about twenty-five years ago that the importance
of these differences was recognized by the late Professor Cope, who
separated them into a distinct order quite co-ordinate with the
lizards, crocodiles, and turtles. These little reptiles, seldom
reaching a length of two feet, have now become so scarce that the New
Zealand government protects them by law from unnecessary destruction;
nevertheless it will probably be only a short time before they become
extinct, the end of a long genealogical line. No other living reptiles
have retained more of the old-fashioned or primitive characters than
this _Sphenodon_ or _Hatteria_, as the animal is called, and because
of them it is of peculiar interest to zoölogists, and especially
paleontologists.
The differences of these beaked lizards from the true lizards are
especially noticeable in the skull, and more especially in the
arrangement of the bones which give articulation to the lower jaws
(Fig. 8). In the lizards and snakes the quadrate bone is loosely
articulated at its upper end with the cranium, and has no inferior
bar or arch connecting its lower end with the jugal and the back part
of the upper jaw. _Sphenodon_, on the contrary, has the quadrate
bone firmly fixed to its adjacent bones at both ends, and is quite
immovable. The vertebrae are biconcave like those of all early
reptiles, not concavo-convex as are the vertebrae of most other living
reptiles. The intercentra or hypocentra, little wedge-shaped bones
between the centra below, are more persistent in _Sphenodon_ than
in any other living land animals except the gecko lizards. Upon the
whole the tuatera is the most old-fashioned of living reptiles, and in
consequence it has nearly lost out in competition with new things.
[Illustration: FIG. 85.—_Sphenodon punctatum_, or tuatera. (From
specimen in the Yale University museum.)]
With these living tuateras we have nothing further to do, since they
are land animals, living about the beaches of the New Zealand islands,
and only occasionally venturing into the water, hiding from their
enemies in the holes in the rocks. But, from some of their antecedents,
from some of their direct forbears perhaps, there have gone off at
different times various branches, whose descendants wandered into
foreign lands or into foreign places, and lived and flourished for a
brief time and then became extinct. Some of these went down into the
water and became more or less aquatic in habit; some, indeed, changed
their forms and habits so greatly that they are often, perhaps rightly,
segregated into different orders. Whether or not they should be called
Rhynchocephalia matters little, however. It is merely a matter of
opinion as to how great the changes should be in order to entitle the
offspring to a genealogical tree all its own. Of these branches there
are two, whose relationships seem to be definite, the Choristodera and
Thalattosauria, though there is more doubt about the latter than the
former. A third group, that included _Pleurosaurus_, seems, from more
recent discoveries, to belong to a different line of descent and has
been described under the Protorosauria.
In the direct line of ancestry there is no known form that was
distinctly aquatic. The oldest known of these, perhaps, is that shown
in Fig. 86, _Sapheosaurus_ from the Jurassic of Solenhofen. Its
resemblance to the modern tuatera is great, and doubtless its habits
were very similar, though its rather long tail and rather short neck
possibly indicate subaquatic habits.
[Illustration: FIG. 86.—_Sapheosaurus_, an Upper Jurassic
rhynchocephalian. (After Lortet.)]
CHORISTODERA
Among the many reptiles of the past which have sought a more congenial
or a safer home in the water few have had a more interesting history,
or a briefer one, than those to which the late Professor Cope gave
the name Choristodera in 1876. Many students of repute consider the
group an order, others a suborder of the Rhynchocephalia. The group,
whether order or suborder, are interesting because of their long and
devious migrations from western North America to Europe, or vice versa,
through rivers and ponds; interesting also because of the persistence
of certain old-fashioned traits that clung to them long after their
disappearance in other animals. Perhaps these traits were among the
causes of their merely moderate success as animals of the water, traits
that led to their early dissolution. Like the proganosaurs, which they
must have resembled in external appearance not a little, they wandered
from their birthplace in the western continent, to perish in the
eastern; and like them their span of existence was short.
Their history among mankind, too, is brief. The first known specimens,
from western North America, were described by Professor Cope in 1876,
under the name _Champsosaurus_. In the following year Professor
Gervais of Paris made known another form from Rheims, which he called
_Simoedosaurus_, so closely allied to the American that even yet
they have not been sharply distinguished. Some years later these
European specimens were more fully described by the well-known Belgian
paleontologist, Dr. Dollo, but it has been only within the past few
years that our knowledge of the animals has been made at all complete
by the discovery and description of several excellent skeletons of
_Champsosaurus_ by Mr. Barnum Brown of New York.
[Illustration: FIG. 87.—_Champsosaurus_; skeleton, as mounted in
American Museum. (Brown.)]
These semiaquatic reptiles never grew very large—not more than four
or five feet in length; nor did they ever succeed in becoming fully
at home in the water, certainly no more so than our modern alligators
and crocodiles. They remained to the end of their comparatively brief
existence essentially land animals, probably seeking their food in the
water but fleeing to the land for protection and for the breeding of
their young. Their chief water adaptations are seen in the elongate
face and flattened swimming tail. Their legs remained essentially
terrestrial, and could have been of but little use in the water for
propulsion; the feet even were doubtfully webbed, or if so, not more
than are those of the alligator. Singularly, like the proganosaurs,
their ribs were heavy and stout, also suggesting bottom-crawling
habits, like those of the living Galapagos lizards. The skull was
lightly built, and the face was long and slender, like that of the
gavials and proganosaurs; but, like those of the former and unlike
those of the latter, the nostrils were situated at the extreme tip.
The hind legs were firmly attached to the body by the sacrum; and no
sclerotic bones of the eyes have been discovered. The neck was neither
unusually long nor unusually short. The body was probably covered with
horny scales.
[Illustration: FIG. 88.—Restoration of _Champsosaurus_.]
[Illustration: FIG. 89.—_Champsosaurus_; skull from above. (After
Brown.)]
To the student of paleontology these animals are of interest because of
the retention of several primitive traits which had long disappeared in
other known reptiles. While the vertebrae had ceased to be perforated
by the notochord, as in the early reptiles, they were still shallowly
biconcave. The first bone of the neck, the atlas, had changed but
little from that of their very ancient forbears of Permian times, and
the bones of the palate still retained numerous teeth scattered over
it, like those of the same Paleozoic ancestors. Most primitive and
old fashioned of all was the pelvis, which was so unlike that of all
known contemporary or later reptiles that, were a paleontologist to
see it without knowing whence it came, he would be almost sure to say
that it belonged to a Paleozoic, or at least a Triassic, reptile, and
not only to an early reptile but a very primitive one at that. This
peculiarity consists in the absence of any opening between the ischium
and pubis, which is characteristic of every living vertebrate with
legs. And these and other old-fashioned characters could not possibly
have been new developments; they must have existed in all the ancestors
of the Choristodera from Paleozoic to early Tertiary times, though not
a single other reptile is known to have possessed them, for the greater
part of this time. Perhaps when Asia and northwestern America have
been more thoroughly explored for vertebrate fossils, some of their
ancestors which perished on their great migration from the western to
the eastern continent in late Cretaceous times will be discovered.
[Illustration: FIG. 90.—Pectoral girdle of _Champsosaurus_. (After
Brown.)]
[Illustration: FIG. 91.—_Champsosaurus_; pelvic bones. (After Brown.)]
The choristoderans began their existence, so far as is now known, in
North America in late Cretaceous times and died out in both Europe
and North America in early Tertiary times. That is, they were one
of the few branches of reptilian life which not only witnessed the
extinction of the great dinosaurs and plesiosaurs, but the advent also
of the early placental mammals. They lived millions of years after the
proganosaurs became extinct, and, similar as they are in form, there
is no relation between them. Moreover, in all probability they did not
migrate to the eastern continent over the same route.
The structure of the head and teeth of the Choristodera clearly
indicates a fish-eating habit, or at least a diet of soft-bodied, free
swimming invertebrates. The legs and ribs, as also the armor of ventral
ribs, like those of the plesiosaurs, point very insistently toward a
bottom-crawling habit while in the water.