CLIDASTES VELOX.
A remarkably complete specimen, referred with considerable certainty to this species, was obtained by ourselves in western Kansas, (Butte Creek) in the summer of 1891. A brief preliminary description of the specimen was given by the senior author in Science, December 8, 1891. A more complete description is here given, which, it is believed, will be of service. The specimen is an unusually perfect one, being very nearly complete, and, as now mounted, shows the bones nearly all in the position in which they were found. The vertebral column is continuous, except in one place, where the tail had been bent up over the back; and complete, save at the very tip of the tail. The skull is complete, or very nearly complete, and has been restored nearly to the condition in life. Figures have been made of this portion of the skeleton, and will be given in a future communication. At present, it may be mentioned that the lacrymals are small, roughly irregular bones, and pointed at either extremity. There are no indications of transverse bones, as there are none in any other skull in the collection.
Cervical vertebrae.
Atlas. The intercentrum is a small bone with three sides of nearly equal extent. The two upper, articular surfaces are gently concave, and meet in a rounded margin; the inferior surface is convex, both antero-posteriorly and transversely, with a roughened prominence in the middle. The lateral pieces have indistinctly separated facets for articulation with the odontoid, the intercentrum and the occipital condyle. The rather short, flattened lamina extends upward, backward and inward, approaching, but not reaching its fellow of the opposite side; it is somewhat dilated distally. Directed outwards and forwards, there is a stout styliform process.
Axis. The neural spine of the axis is elongated antero-posteriorly. It is thin on the anterior portion, but stouter and longer at the posterior part. The large, stout odontoid process is united suturally, as is also the well-developed atlantar hypapophysis, which forms the anterior, inferior portion of the bone. The diapophyses are the smallest of the costiferous series, with only a small articular facet for the rib. The ball is strongly and evenly convex, with its greater diameter transversely. The hypapophysis is the largest of the series; it is suturally united with the stout, exogenous process of the centrum, and projects downward and backward; its distal extremity is roughened for ligamentous attachments.
The third cervical vertebra shows a well-developed zygosphenal articulation, and stout articular processes. The transverse process is small, only a little larger than that of the axis, though, unlike that, it is strengthened by a ridge continued from the anterior zygapophyses. The hypapophysis is smaller than that of the axis, but, like that, is directed downward and backward. The spine may be distinguished from that of any other vertebra by its stout, trihedral shape; it is directed rather more obliquely backward than in the following vertebrae.
The fourth cervical vertebra differs from the third in having stouter transverse processes; in the hypapophysis being directed more nearly downward, and in its smaller size; and in the spine being flattened antero-posteriorly toward the base.
The fifth cervical vertebra differs from the fourth in the broader spine, in the stouter transverse processes, and the smaller hypapophysis.
In the sixth cervical vertebra, the hypapophysis is reduced to a small ossification, scarcely longer than broad, directed downward. The spine has reached nearly the full width of those of the following vertebrae, though somewhat stouter above. The transverse processes are yet stouter.
In the seventh, or last, cervical vertebra the hypapophysis is wanting, or very rudimentary. The under part of the centrum shows a rounded ridge or carina, with a slight projection corresponding to the hypapophysis.
MEASUREMENTS OF THE CERVICAL VERTEBRAE.
Dorsal vertebrae.
There are thirty-five vertebrae between the cervicals and the first non-rib-bearing vertebra, to which the pelvis was, evidently, attached. The distinction between the cervicals and thoracics cannot be made from any characters they possess, as the seventh vertebra does not bear a distinct hypapophysis. Neither can it be said with certainty from this specimen which is the first thoracic vertebra, as the cervical ribs had, unfortunately, been displaced in the collection and preparation of the specimen. In another specimen, referred to C. pumilus, and which, as will be seen later, cannot be specifically distinguished from the present species, short cervical ribs were found attached to six vertebrae posterior to the atlas. That the eighth vertebra is a thoracic one is shown by the relation of the ribs in this specimen. Posteriorly there is no distinction, also, between the true thoracic vertebrae and those of the lumbar region. All the vertebrae anterior to the pelvis bear ribs, and will all be considered as dorsal vertebrae, the true thoracic vertebrae being restricted to those of which the ribs are elongated, and, probably, connected with the sternum.
In the anterior vertebrae of the series, the centra are subcarinate below, the obtuse, rounded ridge becoming less and less apparent until no indications of the keel can be seen, before the middle of the series. The transverse processes are stoutest, with a more elongated, sigmoid articular surface, with little or no constriction, and projecting only slightly beyond the stout articulating processes, in the anterior vertebrae. In the tenth or eleventh, the articular surface has become markedly smaller, more vertical, and less sigmoid in outline. Thence to the last, the articular surface for the ribs remains nearly the same. The process itself, however, becomes gradually more prominent and constricted, as the zygapophyses becomes smaller. The spinous processes increase slightly in length and breadth, and are only slightly oblique throughout. In length, the centra increase gradually. The vertical diameter of the ball increases gradually, while the transverse diameter remains more nearly the same.
MEASUREMENTS OF THE DORSAL VERTEBRAE.
| 1. | Length of centrum to rim of ball | 38 millim. |
| Transverse diameter of ball | 20 | |
| Vertical diameter of ball | 19 | |
| Height of spine above floor of neural canal | 48 | |
| Extent of articular surface of transverse process | 30 | |
| Width of spine | 28 | |
| 4. | Length of centrum to rim of ball | 41 |
| Transverse diameter of ball | 20 | |
| Vertical diameter of ball | 20 | |
| Height of spine above floor of neural canal | 48 | |
| 11. | Length of centrum to rim of ball | 41 |
| Vertical diameter of ball | 22 | |
| Extent of articular surface of transverse process | 16 | |
| Width of spine | 32 | |
| 15. | Length of centrum to rim of ball | 41 |
| Transverse diameter of ball | 21 | |
| Vertical diameter of ball | 24 | |
| 20. | Length of centrum to rim of ball | 42 |
| Vertical diameter of ball | 25 | |
| Height of spine above floor of neural canal | 58 | |
| 24. | Length to rim of ball | 41 |
| Transverse diameter of ball | 22 | |
| Vertical diameter of ball | 23 | |
| Height of spine | 49 | |
| 28. | Length to rim of ball | 40 |
| Vertical diameter of ball | 24 | |
| Transverse diameter of ball | 23 | |
| Height of spine | 54 | |
| 32. | Length to rim of ball | 38 |
| Vertical diameter of ball | 25 | |
| Transverse diameter of ball | 24 | |
| 35. | Length to rim of ball | 37 |
Caudal vertebrae.
Immediately following the thirty-fifth rib-bearing vertebra there is an abrupt change, the tubercular process for the rib giving place to an elongated transverse process. From the position of the pelvis, it is evident that the ilia were attached to the first pair of these. Precisely this relation of pelvis to the vertebrae is found in such lizards as the Monitor and Iguana, and it is probable that such is the relation in all the Pythonomorpha. It will thus be seen that there are no distinctively lumbar vertebrae, if by such are meant free, non-costiferous, pre-sacral vertebrae. The vertebrae of these animals that have been so designated by writers are in reality basal caudal. A distinctive term for them—those with transverse, non-costiferous processes and without chevrons—is needed, and we propose, provisionally, the term pygial. There are seven in the present series, all characterized by elongated transverse processes, and not differing much from each other. The vertebrae lie in the matrix with the ventral aspect uppermost, concealing the spine and upper parts. The under surface is somewhat flattened, and, as in the preceding vertebrae, is gently concave antero-posteriorly. The transverse processes are elongate, stout towards the base, apparently all of nearly equal length, and directed gently backwards and downwards. In the anterior vertebrae the processes spring from near the front part: as the centra become shorter they arise from near the middle. In the last one of the series there are minute indications of chevrons.
MEASUREMENTS OF THE PYGIAL CAUDAL VERTEBRAE.
| 1. | Length to rim of ball | 36 millim. |
| Width of ball | 25 | |
| Expanse of transverse processes | 130 | |
| Width of transverse process near base | 17 | |
| 2. | Length to rim of ball | 33 |
| 3. | Length to rim of ball | 31 |
| 4. | Length to rim of ball | 29 |
| 5. | Length to rim of ball | 28 |
| 6. | Length to rim of ball | 27 |
| Expanse of transverse processes | 130 | |
| Width of ball | 24 | |
| 7. | Length to rim of ball | 27 |
The centra of those caudal vertebrae which have chevrons do not differ much in shape. They become less constricted, and, back of the middle of the series, are smoothly cylindrical in shape. The transverse processes decrease gradually in length, disappearing entirely in the twenty-fifth or twenty-sixth. The spinous processes are more or less incompletely preserved in the anterior vertebrae. They increase only gradually in length for the first twenty of the series, and are markedly oblique, with the posterior border stout, and the anterior border alate. With the twenty-sixth they begin to increase more rapidly in length, and have become more nearly vertical in position, and are thinner at each margin. In the thirty-fifth or thirty-sixth they attain their greatest length, and are here directed slightly forwards. Thence to the end of the tail, the length decreases gradually, and, in position, they are directed more and more obliquely backward. The chevrons are strongly oblique throughout the series and are firmly co-ossified with the centrum.
The tail, it is thus seen, has a broad, vertical, fin-like extremity, which, doubtless, aided much in the propulsion of the animal through the water.
There are sixty-seven vertebrae with chevrons present in the specimen, all continuous, except in one place. The last one is less than one-fourth of an inch in diameter, and shows that there had been yet another, possibly several more. Toward the base of the series the tail has been bent forwards over the back, and it is possible that, where the break occurs, there has been a vertebra lost. The measurements, however, do not seem to indicate any loss. The entire series of vertebrae was not less than sixty-eight, and probably not more than seventy, making for the entire vertebral series one hundred and seventeen to twenty.
MEASUREMENTS OF THE CHEVRON-BEARING CAUDAL VERTEBRAE.
Ribs.
As has already been stated, the cervical ribs were displaced in the present specimen, and measurements of them cannot be given. In a smaller specimen, specifically indistinguishable from the present one, the entire cervical series is preserved with the ribs attached. The first, that articulating with the axis, is very short. The following ones are stouter, but increase only moderately in length, that of the sixth measuring only thirty-five millimeters, while that of the seventh is but a little longer. In the specimen of C. velox described, there is a detached cervical rib sixty-five millimeters in length; it probably belongs with the seventh.
The thoracic ribs are simple, somewhat flattened rods, moderately expanded at the proximal end. The greatest convexity is shown about the middle of the series, where the versedsine of the curvature is forty millimeters, the chord being one hundred and sixty. Posteriorly, the short ribs are only gently curved.
Lying by the side of the vertebral column, and between the ribs, as they have been pressed down, are a number of flattened, soft, punctulate bones, which are evidently the costal cartilages. Posteriorly four rows of them are seen, lying closely side by side, some of them eight or ten inches in length. The sternum, composed of the same material, has been so crushed and crumpled that its shape cannot be made out. The whole structure here, whether of ribs, cartilages or sternum, reminds one very strongly of such lizards as the Iguana or Monitor. There is no indication, however, in any specimen, of an episternum.
MEASUREMENTS OF RIBS.
| Length, first thoracic rib, (chord) | 200 | millim. |
| Length, eleventh thoracic rib, (chord) | 145 | |
| Length, thirteenth dorsal rib | 68 | |
| Length, eighteenth dorsal rib | 64 | |
| Length, thirty-fourth dorsal rib | 52 |
The lengths of the different regions, as they lie in their natural relations, are as follows:
| Skull | 0.420 | meters. | ||
| Neck | 0.225 | |||
| Trunk | 1.360 | |||
| Tail | 1.460 | |||
| Total | 3.465 | 11 ft. 7 in. |
The measurements of an excellent specimen of C. tortor are as follows:
| Skull | 0.630 | meters. |
| Neck | 0.360 | |
| Trunk, (thirty-three vertebrae preserved) | 2.370 |
A very complete specimen of a Liodon in the Museum, in which the complete vertebral column is present, numbering one hundred and seventeen vertebrae, gives the following measurements. The skull is complete, save the most anterior portion.
| Skull (approximated within narrow limits) | 0.700 | meters. | |
| Neck | 0.430 | ||
| Trunk | 1.760 | ||
| Tail | 3.420 | ||
| Total | 6.310 | 20 ft. 8 in. |
The vertebral series in this specimen is composed of seven cervicals, twenty-three dorsals, seven pygials, and eighty chevron-caudals.
The relative proportions of the different regions in the two genera, as shown by the two specimens of Clidastes and Liodon, may be represented as follows. The first column is for Clidastes.
| Skull | 12.1 | 11.1 |
| Neck | 6.5 | 6.8 |
| Trunk | 39.2 | 28.0 |
| Tail | 42.3 | 54.1 |
Limbs.
The figures in plates II and III will give a sufficiently good idea of the limbs in this specimen. They are figured as they were lying, showing the outer sides of the coracoid, scapula and pelvic bones, and the palmar or plantar surface of the remaining bones.
Coracoid.
It will be observed in plates II and IV that there are two very different types of coracoid, one with a deep emargination, the other without the slightest indication of such. The same non-emarginate form occurs in C. tortor, as specimens in our Museum show, in C. propython Cope (Ext. Batr. etc. pl. xii, f. 16,) and in C. dispar, as figured by Marsh[7], and as stated by him in the same paper (“There is certainly no emargination in the coracoid of Clidastes, Edestosaurus and Baptosaurus, as specimens in the Yale Museum conclusively prove.”) It is true that Marsh in a later paper[8] figured a specimen with emarginate coracoid under the name of Edestosaurus dispar, but it is certain that his identification of his own species was wrong, as will be seen by comparing his figures. From the senior author’s memory of the specimen with the emarginate coracoid figured, and from the figure itself he feels confident that the second specimen is C. velox.
That the emargination was overlooked by the author seems strange, as in the same paper in which this figure is given occurs the description of Holosaurus, founded upon that very character. If the emargination is sufficiently important to base a genus in the one case, then it should be in the other, and the character could not be applied to Edestosaurus, based upon characters which it hardly seems possible that the author himself could seriously consider, for E. dispar was the type of Edestosaurus.
It will be observed, further, that the figured coracoids differ very materially in size, those with the emargination pertaining to a small species, while C. dispar is one of the largest. In our Museum there are three specimens with the emarginate coracoid, all of them small or very small, the described specimen of C. velox being the largest.
The point of chief interest in this relation is the value that can be given to this character. Is it individual, specific or generic? Marsh has called it generic, but we think an examination of the two very complete specimens of C. tortor and C. velox in our Museum will convince any unprejudiced student that he is in error.
A comparison of the figures herewith given of the paddles will show their great resemblance, and these two forms of paddles have been figured because the species are the most unlike of any that we know in the genus. As all the small specimens seem to possess this character, and as they cannot be called immature specimens, we believe the character is a specific one. As Marsh says, typically both Clidastes and Edestosaurus have a non-emarginate coracoid, so that neither name could apply to the emarginate form, were it generically distinct.
Our Museum also contains both forms of the coracoid pertaining to the genus Platecarpus, of which Holosaurus is a synonym.
While studying the specimen above described, a striking similarity was observed to several other specimens already determined with confidence as C. pumilus Marsh. A more careful comparison failed to bring out any real differences beyond size, and even this was shown to be very inconstant.
The following comparison of the descriptions given by Marsh will be of interest.
The description, otherwise, shows no discrepancies of importance. The chief difference given by the author is the size, and this character we think our specimens show to be of little specific value. “It is a question of some importance how far difference in size among the Mosasauroids may be a test of difference in species. Among the numerous remains of these animals which have been discovered I have never yet observed any which presented any evidence relative to age. * * * In this view of the case, some of the many described species of Mosasauroids may have been founded on different sizes of the same.”[9]
The length of the cervical vertebrae in the specimen above described is thirty-seven or thirty-eight millimeters. The cervical vertebrae in two specimens referred to C. pumilus have lengths respectively of twenty-two and thirty millimeters. In the type specimen of C. velox they must have had a length of at least forty-two millimeters.
It thus appears that, between the smallest specimen, which, in life, could have hardly exceeded eight feet in length, our specimens, indistinguishable anatomically, represent forms of ten and twelve feet, while the type itself was about fifteen feet in length.
Of the material originally referred to C. pumilus, there are in the collection five or more specimens, which, altogether, furnish nearly every part of the skeleton. They present no tangible differences from the skeleton of C. velox described above. There can be, hence, little or no doubt but that the name C. pumilus is a synonym.
It is hardly possible to say with certainty that C. affinis Leidy is or is not the same as C. velox, but, so far as the description goes, we can find few differences. The type is of about the same size as the type of C. velox, and the figures agree well with the bones of the skeleton described. Although the description was not published till 1873, the author makes no mention of the species of Marsh’s. Leidy describes the back teeth as having the enamel strongly striated, with the surface presenting evidences of subdivision into narrow planes. In this respect, only, it disagrees with the specimen.
Plioplatecarpus Dollo is described by its author as having a sacrum of two conjoined vertebrae,[10] by reason of which it is placed in a separate family from the rest of the Pythonomorpha. It may be presumptuous to express a doubt of the genuineness of the sacrum, and yet, save from the fact that the author found two specimens quite alike, one might doubt it strongly. It is not very rare that two, or even three vertebrae are found united from injury in these animals, and such would readily account for the consolidation as figured and described by Dollo, except for the coincidence of the second specimen. A stronger reason for doubt is the statement that the consolidated vertebrae belong to the posterior “lumbar” region, and that the last vertebrae had small tubercles indicative of chevrons. In the reptiles which we have examined, the chevrons do not begin immediately behind the pelvis, but are separated by a longer or shorter region in which the vertebrae bear elongated diapophyses alone. If the conjoined vertebrae figured by Dollo are in reality sacral, it would appear that the animal is an exception to Clidastes and such lizards as we have examined. Furthermore, the pelvis must have been of a different structure from that in the Kansas genera of the Pythonomorpha, for, in these, it is evident that the ilium had an oblique position, and could have been attached to but a single diapophysis.