Samuel Wendell Williston

“ In the extreme elongation of the neck, Elasmosaurus exceeded all other vertebrated animals of the past or present, and was, if we assume a diphyletic origin of the short-necked forms, the most specialized of all plesiosaurs, since in no other genus do we know of any species having as many as fifty cervical vertebrae. ”

“ Elasmosaurus serpentinus Cope. Niobrara Cretaceous of Nebraska. This species was based upon much better material than was either of the foregoing ones, and it is both recognizable and distinct. Unfortunately, no figures have ever been given of the type specimen, and I have not had, so far, an opportunity to study the specimen. As in his other descriptions, Cope identified some of the vertebræ wrongly. The first dorsal vertebra, as he describes it, is in reality a posterior cervical, while his seventh is either the last pectoral or the first true dorsal. ”

“ The type of the genus and species Cimoliasaurus magnus Leidy is a number of dorsal and cervical vertebræ from Monmouth county, New Jersey, probably from rocks of an epoch corresponding with the Fort Pierre Cretaceous, and they have been, for the most part, well figured by Leidy in his "Cretaceous Reptiles." With the original specimens he later associated a series of fourteen vertebræ, or rather centra of vertebræ, from the same locality, and he speaks of such bones being common in the deposits of New Jersey. ”

“ That they pertain to a long-necked form is quite certain, and the general characters of the vertebræ are like those of Elasmosaurus.
The dorsal centra are nearly circular in outline, somewhat broader than high, with their sides gently concave. The diapophyses are stout, directed upward and outward to a plane above the zygapophyses. The zygapophyses are separated by a notch and are rather small. The spine is flattened and elongate. Figures of these vertebræ will be given in a later communication. ”

“ Unfortunately, the type specimen of Elasmosaurus no longer has the girdles described by Cope. What has become of them is not known. There are some parts of these, especially the clavicular arch, that are necessary for a correct understanding of the genus. However, from an attentive study of this type specimen and of several other specimens which can be with much probability, if not certainty, referred to the same species, I am enabled to give the following characters for the genus Elasmosaurus. Those characters derived from the type specimen or type species are given in italics ”

“ Professor Marsh had not definitely determined any of his species, and had only tentatively located some of them in genera, aside from the Jurassic species described by him as Pantosaurus striatus. Most of the observations of his notes have been anticipated by myself or others; others new to me I shall fully acknowledge in each case. The present paper will deal chiefly with this material, that especially belonging to the genus Elasmosaurus. Other material in the collection will be discussed in later papers, so far as the more important characters are concerned. ”

“ The ribs are of course single-headed; the spines are broad and not very high; the posterior dorsals are more flattened at their extremities, and their articular rims are sharp, with slight crenulations. ”

“ From drawing of articulated specimen, American Museum of Natural History. be distinguished from each other. Its relationships are nearest with the genus Cryptoclidus of Europe, a figure of the pectoral girdle of which, copied from a drawing kindly made for me from an articulated specimen in the American Museum of New York City, is given herewith (text-figure 1) . But the two genera are very distinct. ”

“ Coracoids broadly separated posteriorly to the interglenoid thickening, the posterior end not much dilated. Cervical ribs single-headed. Ischia short. Skull short; parietal crest much elevated; supraoccipital bones parial; palatines separated by pterygoids. Cervical vertebræ from sixty to seventy-six in number. ”