Crocodilus aptus, Leidy.
Contributions to Extinct vertebrate fauna of the Western Territories,
p. 126.
Henry's Fork.
Crocodilus Grinnelli, Marsh.
American Journal of Science and Arts, vol. i., p. 465.
From Cottonwood Creek.
Crocodilus Elliotii, Leidy.
Cont. to Ex. Vert. Fauna, p. 126.
Represented by a perfect skull, and several vertebræ.
This fossil exhibits a form of skull which shows characters of both
crocodile and alligator; the latter to a less marked degree. That it
properly belongs to the former genus is shown by the notch in the
upper jaw which receives the canine of the lower.
The entire skull is remarkably flat on its upper surface, the face
and cranium being nearly in the same plane without the descent at the
frontals usual in these reptiles. The jaw is deeply notched at the
sutures between the maxillaries and pre-maxillaries, and the second
maxillary notch is well marked. All the bones of the upper surface of
the head are deeply pitted.
The borders of the cranium are rounded as they approach the orbits;
the superior temporal orifices are almost perfectly circular,
the fore-and-aft diameter exceeding the transverse by only one
millimetre. This effect may, in some degree, be due to distortion.
To give a more detailed account of the several elements of the skull,
we take up first the _basioccipital_. This bone is remarkably long
and straight, tapers gradually downwards, and becomes quite narrow
at the distal end. It is smooth throughout, and exhibits no rugose
muscular attachments, such as are sometimes seen in other members of
the order. The condyle is large and nearly spherical, but with median
groove distinctly marked. In size and shape it is more like that of
the alligator than of the ordinary crocodile, but it is somewhat
different from either. It differs from the former, in not having so
long a neck distinctly marked by a constriction; and from the latter,
in not having additional articular faces on each side of the condyle
proper. As far as can be judged, no portion of it is formed by the
exoccipitals. Below the condyle the basioccipital is perforated by
two small vascular foramina; the spheno occipital canal occupies the
usual place, and is very large.
The _exoccipitals_ are large, of very great width, but rather low
from above downwards. The position of the foramina which perforate
these bones is peculiar; it resembles more the arrangement seen in
the skull of the alligator than in that of the crocodile, but it has
an additional foramen. There are, then, two small venous foramina
near the condyle; while along the lateral margin of the occiput,
are placed in a vertical line the foramina for the hypoglossal and
pneumogastric nerves, and the internal carotid artery. The foramen
for the facial nerve, etc., is situated in the usual place, and is of
the usual size. The foramen magnum is heart-shaped, low, wide above,
contracting below. The paroccipital processes are long and slender,
and project strongly backwards.
The _supra-occipital_ is very small. It shows to some extent on
the upper surface of the skull, wedged in between the parietals.
As a whole, the occiput is of remarkable shape: it is perfectly
vertical, as in all other crocodilians; is remarkably high from
above downwards, and is very broad at top, becoming extremely narrow
distally. This latter feature is owing to the peculiar shape of the
pterygoids; which, when viewed from behind, do not appear to reach
the basioccipital.
The _basisphenoid_ is so destroyed by crushing, that nothing can be
said of its shape or of its foramina. It was, however, evidently
very stout. The alisphenoid is large and smooth and is not ridged;
the _foramen ovale_ is small, and is not produced into an anterior
notch. The suture between the alisphenoid and the pro-otic are quite
distinct, but the latter is so firmly anchylosed to the quadrate that
its limits are indeterminable. None of the other periotic bones are
visible.
The _quadrate_ is very long and broad. In shape it resembles the
corresponding bone of the alligator, but is somewhat broader. The
lower surface is divided into two unequal parts by a conspicuous
ridge, which runs to within an inch of the articular surface. This
surface has a more decidedly grooved or trochlear appearance than in
the common crocodile; but not to the same degree as in the specimen
described by Dr. Leidy. It is more like the Mississippi alligator in
this respect than any living species of which we have specimens.
The _pterygoids_ are of peculiar shape; they are long, slender, and
pointed, and meeting the basioccipital on the median line in front,
they project downwards and backwards. Their posterior border is very
deeply emarginate, so that they seem to have no connection with
each other, or with the basioccipital; instead of having the broad,
plate-like appearance of these bones in recent species. The suture
between these on the palatal surface is long; and the processes of
the pterygoids, which bound the posterior nares, are long and stout.
The posterior nares have the position which they take in the recent
species; they are visible in the occipital surface, and are directed
backwards as well as downwards. They are rather small, and appear
to have no septum between them, but this cannot be said with any
certainty.
The _transpalatine_ is also somewhat peculiar in shape; the process
which joins the pterygoid is of great length, being nearly as long
as that bone. The other limbs are more normal in length. The three
processes are connected at the usual angle.
The _palatals_ are long and narrow, becoming wider anterior to the
foramina. The suture with the maxillaries is rounded, and there are
no forward processes as in the true crocodiles; but at the same time,
these bones are not of the shape exhibited in the alligators. The
palatal foramina are of immense length; they are more than one third
as long as the entire bony palate. Their width is also considerable.
The _maxillaries_ are long and very broad; the alveolar border is of
about the same shape as in the crocodile, but less decidedly sinuous;
and the posterior part passes in below the alveolus of the lower
jaw. The convexity of the upper surface of the maxillaries is not
so well marked as in the true crocodiles. It is nearly as flat as
in the alligator. The palatine plates of the maxillaries are short,
broad, and nearly flat, arching slightly to form the alveolus, and
perforated along this border by rows of foramina.
The _premaxillaries_ are very short; they curve strongly outwards
from the notch and enclose the large anterior narial opening, which
is distinctively crocodilian (as distinguished from other genera)
in shape. The muzzle ends quite sharply. The palatine processes are
short and convex in both directions, and the incisive foramen is
heart-shaped. The alveolus is quite regular in outline; it is pitted
in front for the first mandibular teeth, but there is no perforation
for them.
The teeth are short, stout, compressed so as to form cutting-edges,
and are somewhat obtuse. They are finely striated from base to tip.
The premaxillary held four teeth; these are all broken off, but from
their fangs it appears that they formed an uninterrupted row, and
were subequal in size. The maxillary accommodated fifteen teeth, of
which the fifth is the largest, and forms a very prominent canine.
The posterior maxillary teeth are proportionately larger, and more
equal than in either crocodile or alligator.
The _nasals_ are rather broad; they send processes into the
anterior narial opening, which tend to divide it, but this division
was probably not complete. The limits of the _prefrontals_ and
_lachrymals_ are so obscure as to preclude description.
The _frontals_ are long and very narrow, though wider than in the
alligator. They are smooth and flat, exhibiting no concavity on top.
They expand considerably at the posterior part of the orbit, at the
sutures with the post-frontals. These bones are long, stout, and
curved very strongly outwards.
The _mastoids_ are of remarkable size; they project far backward
along the tympanic, and encroach largely upon the occipital region.
It is partly owing to this that the occiput is so high.
The _parietals_ are short, and very narrow between the temporal
orifices, behind these they expand considerably. The orbits are large
and of irregular shape.
The _malar_ is long and rather slender.
_Measurements._
M.
Length from occipital border to end of muzzle ·455
Breadth of cranium at postorbital angles ·0935
Breadth of cranium between temporal orifices ·019
Breadth of forehead between orbits ·036
Breadth of temporal orifices ·037
Fore-and-aft diameter of the same ·038
Fore-and-aft diameter of the orbits ·073
Length of face in advance of the orbits ·3055
Breadth of face outside of the fifth maxillary tooth ·176
Breadth of muzzle as formed by premaxillaries (about) ·114
Breadth of muzzle at notch for canine ·093
Length of premaxillaries to notch ·080
Estimated length of entire alveolar border ·283
Breadth of articular surface of quadrate ·059
Vertical height of occiput ·124
Vertical diameter of foramen magnum ·016
Transverse diameter of foramen magnum ·025
Vertical diameter of condyle ·023
Transverse diameter of condyle ·028
Length from palatine foramen to end of pterygoid ·120
Length of palatals ·1295
Length of palatine foramen ·142
Greatest breadth of palatine foramen ·051
Length of bony palate from incisive foramen to
posterior nares ·350
The _mandible_ is long, rather shallow, but very thick. The symphysis
is very long, extending as far as the seventh tooth. The chin is
quite sharp, but becomes broad, as the rami diverge quite rapidly.
The alveolar border is rounded and comparatively straight, the median
enlargement of the dentary is in thickness rather than in height.
The two rami diverge at an angle which is more open than in the
true crocodiles, and less so than in the alligator. The mandibular
foramen is smaller than in the latter genus, but corresponds with it
in position; it has its long diameter parallel with, and not oblique
to, the alveolus. The mandibular fossa is extremely large and deep.
The splenial is long and stout, ends obtusely, and does not reach
the symphysis. The articular cavity is broad from side to side, but
rather shallow; it is not divided into two distinct facets as in the
alligator. The post-glenoid process is very stout; it projects but
slightly upwards, less so than in either crocodile or alligator. It
has no median ridge as in the former genus, and is tuberous at the
end.
The teeth are much like those of the upper jaw, but are somewhat
sharper and more conical; they are not recurved, and have no distinct
constriction, as is found in most of the recent species. There are
about eighteen teeth to each ramus; the first is large and sharp, and
is followed by two small ones and then by the canine. The remaining
teeth do not exhibit any great differences of size.
_Measurements._
M.
Length of rami (straight) ·618
Width of lower jaw outside of glenoid cavities ·316
Length of symphysis ·110
Width of jaw at second enlargement ·057
Depth at oval foramen ·073
Greatest width at symphysis ·110
Space occupied by teeth ·340
Breadth of glenoid cavity ·072
Length of post-glenoid ·065
_Vertebræ._
_Cervicals._--The centra are long and nearly cylindrical, expanding
slightly near the anterior face. The hypapophyses are short and
broad; they project forwards, and are somewhat compressed. The
vascular foramina correspond in size and position to those of
the alligator. The neural canal is small and subcircular, having
comparatively short but very stout neurapophyses, which are
perforated behind the diapophyses. These are short and stout, and are
developed from the neurapophyses alone. The zygapophyses are long
and flat; the anterior ones project almost vertically. The neural
spines are stout, and of greater antero-posterior extent than in the
alligator.
_Dorsals._--A few of the anterior dorsals have strong hypapophyses.
The centra of all are long and stout. The neural canal is smaller
than in the cervical region; it has strong neurapophyses, which
develop long and depressed diapophyses. The neural spines are low
and broad. The zygapophyses are developed on the laminæ, and do not
project upwards as in the cervical region.
The _lumbars_ are much like the dorsals, except that they are longer,
and have very large and depressed diapophyses, which project somewhat
upwards.
_Measurements._
M.
Length of centrum of a posterior cervical ·049
Height of neural canal ·015
Fore-and-aft diameter of neural spine ·023
Length of diapophysis ·023
_Dorsal._
M.
Length of centrum ·0555
Length of hypapophysis ·018
Fore-and-aft diameter of neural spine ·030
_Lumbar._
M.
Length of centrum ·057
Fore-and-aft diameter of neural spine ·0285
Diameter of diapophysis ·029
The dermal scutes are long ellipses, deeply pitted on one side, but
without a trace of a keel. Their edges show no signs of sutural union.
The bones described indicate a reptile about fifteen feet long. They
were found near Smith's Fork, Wyoming.