Williston, S. W. 1890.
Structure of the Plesiosaurian skull.
Science 16(405):262 and 16(407):290.
Copyright © 2002-2010 by Mike Everhart
Created 01/15/2003 - Updated 03/09/2010
Wherein, S.W. Williston describes, for the first time, an intact skull of an American plesiosaur (Styxosaurus snowii, KUVP 1301, currently in the exhibits of the University of Kansas Museum of Natural History), including the first evidence of a sclerotic ring. To date, this is the only known skull of an elasmosaur from Kansas.
Structure of the Plesiosaurian Skull.
IT is somewhat remarkable, that, in a group of fossil reptiles like the plesiosaurs, the nature and structure of the skull should have remained for so long a time practically unknown. Fragmentary remains of this very important part of the skeleton are not rare in collections, but none sufficiently complete to make out any thing at all satisfactory of its anatomy have hitherto been described. Very fortunately the museum of the Kansas University has recently been enriched by the skull and a large part of the neck of one of these animals, in most remarkably perfect preservation, collected from the Kansas Niobrara cretaceous by Judge E. P. West, assistant in paleontology at the State University. Recognizing the value and rarity of the specimen, Dr. West used the most scrupulous care in removing and shipping the specimen, and, as now cleaned from its matrix in the museum, it permits most of its structure to be made out with certainty and ease. I have in preparation a full description of the specimen, with illustrations, which will shortly be published in the "Transactions of the Kansas Academy of Sciences." Meanwhile, however, the very great importance of the find renders a brief description of its chief characters at the present time very desirable. The species I refer provisionally to the genus Cimoliasaurus [sic], though certain characters, as will be seen, do not accord with those given by Lydekker in his recent "Catalogue of Fossil Reptilia," The specimen lies upon its side, with twenty-six vertebrę in position; and all, save some of the posterior vertebrę, which were exposed, are in perfect preservation. The cervical vertebrę have the arches and riblets fully co-ossified with no or but very slight traces of their sutural attachments. There is but a single rib attachment, and the zygosphene is rudimentary, The spines are short; the anterior centra, gently cupped; the posterior ones, which increase gradually in slenderness, more deeply so. The parietal bone forms a roof- shaped covering, ascending into a high, thin sagittal crest two or three inches above the brain-case: there is no parietal foramen. There is but one temporal arcade, a broad bar passing directly backward, on a line with the maxilla, to unite with the lower part of the quadrate, The limits of the quadrato-jugal have not yet been satisfactorily made out. The post-orbital is a slender bone uniting broadly with the jugal below, and has no connection with the slender squamosal. There is apparently no post-frontal. Lying within the comparatively small orbit are eleven or twelve sclerotic plates, touching each other at their edges, and forming the larger part of a ring, a few having been misplaced. The mandibular symphysis is short, and the two sides' are so firmly co-ossified that I have found no trace of the suture. There are about twenty teeth in each jaw, extending far back, the anterior ones very much larger than the posterior ones; in the locked jaws the upper ones reaching nearly to the lower margin of the stout mandible. A part of a single bone was found between the jaws, which I believe to pertain to a hyoid.
I need not point out the importance of the foregoing characters. Others scarcely less interesting will he given later. The ones here given, however, are nearly all in conflict with generic, family, ordinal, or even super-ordinal characters hitherto accepted, The sclerotic plates are the first ones described for any of the Synaptosauria, a branch comprising the Chelonia and Sauropterygia.
The species can be located with neither Polycotylus or Elasmosaurus, the two genera of the American cretaceous hitherto described as having co-ossified neural arches. I place it, however, under Cimoliasaurus [sic], in Lydekker's acceptation, and shall describe and figure it under the name C. Snowii, in honor of Chancellor F. H. Snow, who has done so much for the development of the natural-history department of our university, I append a few measurements: length of skull from occipital condyle to top of premaxilla, 18 inches; greatest height of skull to top of parietal crest, 9 inches; length of centrum of second cervical vertebra, 1 3/8 inches; height of centrum of second cervical vertebra, 1 3/8 inches; height of spine above centrum. same vertebra, 2½ inches; length of centrum of eighteenth cervical vertebra, 2¾ inches; height of centrum, same vertebra, 2 inches; length of centrum of twenty-fifth cervical vertebra, 3 5/8 inches. S. W. WILLISTON.
University of Kansas, Oct. 25.
[VOL. XVI. No. 407
Structure of the Plesiosaurian Skull.
IN his recently published "Manual of Paleontology" (p. 1067) Lydekker makes the statement, in his definition of the Lynapto- saurian branch, that there are "no ossifications in the sclerotic of the eye," and repeats it in his yet more recent "Catalogue of Fossil Reptilia." Upon this authority, I stated in my recent letter to Science that sclerotic plate's had not been previously described for this branch, including the Chelonia and Sauropterygia. This is not correct, as Dr: Baur kindly informs me. He says, "Sclerotic plates are present in the Testudinata, as mentioned by Huxley and Hoffmann. I have found them in Pleurodira, Cryptodira, and Trionycha."
I do not wish to say that this character, and certain other ones, such as the co-ossification of the jaws, absence of parietal foramen, etc. , are of high classificatory value, but rather that their discovery will require a revision of definitions hitherto given.
S. W. WILLISTON. Lawrence, Kan., Nov. 12.
Nicholson, H. A., and Richard Lydekker. 1889. A manual of palaeontology for the use of students, with a general introduction on the principles of palaeontology. 3d ed., London, vol. II xi + 889-1624, figs. 813-1354. 1st and 2nd eds.
Lydekker, Richard 1890. Catalogue of the fossil Reptilia and Amphibia in the British Museum. Part IV. Containing the orders Anomodontia, Ecaudata, Caudata, and Labyrinthodontia; and supplement. London. xxiii + 295 pp., 66 figs.
Williston, S. W., 1890. A new plesiosaur from the Niobrara Cretaceous of Kansas. Trans. Kansas Acad. Sci. xii pp. 174-178, with 2 fig.