Original Document
Original Document
Joseph Leidy, "Remarks on Elasmosaurus platyurus," 1870.

[Wherein Dr. Leidy reported that E. D. Cope had restored Elasmosaurus platyurus with the head on the wrong end, and admits his own error in the earlier identification of vertebrae from Cimoliasaurus magnus Leidy 1851.]

March 8

Dr. Carson, Vice-President, in the Chair.

Twenty-five members present.

PROF. LEIDY made the following remarks: The reptilian remains from the cretaceous formation near Fort Wallace, Kansas, presented to the Academy by Dr. T. H. Turner, and described by Prof. Cope under the name of Elasmosaurus platyurus, belong to an Enaliosaurian, as originally suggested by Prof. Cope. The anatomical characters of the different regions of the vertebral column, those of the shoulder and pelvic girdles, and of the preserved portions of the skull and teeth, are decidedly Plesiosaurian.

Prof. Cope has described the skeleton in a reversed position to the true one, and in that view has represented it in a restored condition in fig. I, pl. ii. of his "Synopsis of the Extinct Batrachia and Reptilia," Pt. I, August, 1869, published in advance for fourteenth volume of the Transactions of the American Philosophical Society. To explain the apparently anomalous and reversed arrangement of the articular processes (zygapophyses) of the vertebrae, he has supposed that those as ordinarily existing are substituted by the second set of articular processes (zygophene and zygantrum), as found in serpents and iguanians (Proc. Bost Nat. Hist. Soc. xii, 265; Syn, Ext. Bat. and Rept. 42).

The finding of a portion of the jaws, as reported by Dr. Turner, in the vicinity of what Prof. Cope has supposed to be the cervical portion of the skeleton, and which he considers as confirmatory of the view he has taken of its position, without further consideration, is more than compensated in the opposite end of the column terminating in a c??ssified axis and atlas, as is the case also in the mature Plesiosaurus. The cup of the atlas still retains the hemispherical occipital condyle.

The Kansas saurian was wonderful for the length of its neck, far exceeding in this respect the Plesiosaurus. The vertebrae in the specimen form a nearly unbroken series to the seventy-sixth inclusive. If we regard all as cervical until the transverse processes begin to spring in part from the spinal arch, it will comprise the extraordinary number of seventy-two. In the different species of Plesiosaurus, so far as known, the number ranges from twenty-four to forty-one. The length of the neck, independent of the head, was about twenty-two feet.

The cervical vertebrae successively increase in length to about the forty- fourth, then remain nearly the same to the sixtieth, and afterwards gradually decrease. The atlo-axis is about 2 1/4 inches long; the third cervical is 1 1/2 inches; the tenth nearly 2 inches; the twentieth 2 3/4 inches; the thirtieth 3 1/2 inches; the fortieth 4 inches; the forty-fourth 4 1/2 inches, and so to the sixtieth; and the sixty-eighth to the last one about 3 3/4 inches, which is also about the length of the succeeding four dorsals.

The imperfections in the remainder of the vertebral column of the Kansas saurian do not permit a positive estimate to be made of the comparative extent of the trunk and tail.

A comparison of the caudal vertebrae of isolated specimens from the cretaceous formation of Alabama, Mississippi and New Jersey, leaves but little doubt that Elasmosaurus is identical with Discosaurus. Such also appears originally to have been the opinion held by Prof. Cope in regard to a portion of the same skeleton, which he referred to a species with the name of Discosaurus carinatus (LeConte's Notes on the Geology of the Survey of the Union Pacific Railroad, 1868, p. 68).

Specimens of vertebral bodies from the New Jersey green sand, referred to Cimoliasaurus (Cret. Rept. of the United States, pls. v, vi), and supposed by me to belong to the posterior part of the column, are seen by comparison with the Kansas skeleton to be cervical and perhaps anterior dorsals. The difference in the proportions of the corresponding vertebrae; appear to indicate the genus to be distinct from Discosaurus.

The imperfect vertebral specimens from Arkansas, originally referred to Brimosaurus (r. Acad. Nat. Sci. 1854, 72, pl. ii, figs. 1-3) are probably posterior cervicals of Discosaurus.

In the true view of Discosaurus and its allies, the so-called order of Streptosauria (Proc. Bost. Nat. Hist. Soc. 1869, 265; Synopsis Ext. Batr. and Rept., 40) fails to maintain its position.

The extensive shoulder and pelvic girdles of the Kansas saurian, so much like those of Plesiosaurus, were most probably provided with limbs constructed like those of the latter animal.

In its restored condition Discosaurus would appear to have resembled Plesiosaurus in its form as ordinarily represented, excepting that it possessed a much longer neck, –one indeed that exceeded that of all known animals. We may imagine this extraordinary creature, with its turtle-like body, paddling about, at one moment darting its head a distance of upwards of twenty feet into the depths of the sea after its fish prey, at another into the air after some feathered or other winged reptile, or perhaps when near shore, even reaching so far as to seize by the throat some biped dinosaur.

Credit: Proceedings of the Academy of Natural Sciences of Philadelphia vol. 22, (1870), 9-10.
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