Champsosaurus Cope ED 1876

CHAMPSOSAURUS, Cope. Genus novum. Vertebrae of more than a hundred individuals referable to several species. which I obtained from the Judith River beds of the Upper Missouri region. present characters which demand the establishment of a new genus for their reception. The characters presented by the vertebral column are the following: The ribs have a single head, which articulates with a prominent tuberculum. excepting those of the cervical vertebra. On these there is a small capitular tubercle below the diapophysis. lt commences very small and inferior in position. being removed, in fact, but a short distance from the inferior middle line in the first vertebra in which it appears. It rises rapidly in the succecding centra until it is merged in the tuberculum of the diapophysis. The latter projects from the neural arch, which is free from lhe centrum, but in none does the base of the diapophysis rise from a point above the floor of the neural canal. On the dorsals it is vertically compressed. One of the anterior cervicais, probably the axis, is obliquely truncated below its anterior articular face, for a free hypopophysis or os odontoideum. This vertebra has no parapophysis, and the articular faces for the neuropophysis are superior. The few vertebrae in each of several series, probably from the sacral region. are more depressed than the others, and the facets fur the diapophyses present a greater antero-posterior extent, but none are coössified. The caudal vertebrae are distally quite compressed. In all, except the anterior ones, the neural arch is coössified with the centrum. and in such there are no diapophyses. In those with free neural arch, the facets for the neuropophyses turn down on the sides of the centrum. The articular extremities of the centra are plane, those of the caudal series slightly concave. There are no hypapophyses behind the axis, excepting a longitudinal carina, which ceases to exist on the dorsal vertebrae. The zygapophyses are simple. The chevron bones are free. The relations of the atlas and axis, though not fully elucidated by my specimens, are peculiar. The former has separate neurapophyses, which have nearly the shape of those of the Streptostylicate Reptilia, resembling much those of the Pythonomorpha. Although I procured numerous cervical vertebrae, there are but few which exhibit the antero-inferior facet for supposed hypapophysis, already described. The position of this vertebra was in front of the first cervical which displays: a parapophysis, and is, on this account, likely to be the axis or the third cervical vertebra. It is the more probably the axis, as there is no other among the large number of vertebrae in my collection which can he referred to that position. Its anterior articular face is smooth and like the posterior, showing that the odontoid bone was not coössified with it. Now in the Crocodilia the odontoid bone is united with the anterior extremity of the axis by suture, which may become coössified with age, while the free hypapophysis is wanting. In the streptostylicate orders the hypapophysis is present, and the odontoid is above it, but united to the axis by suture. On the other hand, in the Rhynchocephalia, the axis is coössified with both odontoid and hypapophysis, and a few succeeding vertebrae possess free hypapophyses. Thus it is possible that I am yet unacquainted with the axis of Champsosaurus. One entire rib and the heads of several others are all that were obtained. The former is from the anterior part of the dorsal series, and is stout and short. The head is truncate and compressed, its articular face is contracted, forming a narrow figure eight. The shaft is obliquely flattened. The extremities are separated from the lateral surfaces by a narrow angle, as though capped with cartilage in life, as in the Pythonomorpha. Bones of the extremities are very rare. One fragment resembles the proximal end of a crocodilian tibia, and another is like the distal half or more of the tibia of the same type. There is considerable resemblance between the vertebrae of this genus and those of Hyposaurus, Ow., from Cretaceous No. 5, of New Jersey, but the relations of the axis and atlas in that genus are as in other Crocodilia, and not like those seen iChampsosaurus . The absence of sacrum precludes the possibility of regarding this form as dinosaurian. It rather seems to share some rhynchocephalian characters with general amphiplatyan crocodilian resemblances. The shortness and robustness of the thoracic ribs is a feature quite unique, and reminds one of the Batrachia. The teeth are unknown in their true relations, but there are several types in the collections which may be found to belong here. These are of the rhizodont character. As a summary of the preceding, I propose to refer the genus Champsosaurus to the order Rhynchocephalia, provisionally. It differs very much from the typical genus of that order, Sphenodon, in the non-coössification of the sacral vertebrae, and non-union of the neural arches of the vertebra: with their centra, and the absence of the chordal perforation of the latter. It diifers from the extinet genera. Clepsydrops and Cricotus, Cope, in the last mentioned two characters. Ou these grounds it may constitute a distinct suborder, under the name of Choristodera. It is possible that the tooth, which I referred to anew genus and species, under the name of Paronychodon lacustris (Proeeedings Academy, 1876, October), may belong to one of those of the present genus. In that case the older generic name takes precedence of the later. I may add that some vertebrae of this genus have been figured and described by Dr. Leidy in the Transactions of the American Philos. Society, 1860, without name. I recognize four species among the vertebrae, chiefly by characters observed in the cervical region. There is a great discrepancy of size among them, and the small ones may be immature.Published as part of Cope, E. D., 1876, On some extinct reptiles and batrachia from the Judith River and Fox Hills beds of Montana, pp. 340-359 in Proceedings of the Academy of Natural Sciences of Philadelphia 28 on pages 348-350, DOI: 10.5281/zenodo.336836