File:Image from page 249 of "Water reptiles of the past and present" (1914) (14586635547).jpg

Identifier: waterreptilesofp1914will Title: Water reptiles of the past and present Year: 1914 (1910s) Authors: Williston, Samuel Wendell, 1851-1918 Subjects: Aquatic reptiles Publisher: Chicago, Ill., The University of Chicago Press Contributing Library: Boston Public Library Digitizing Sponsor: Boston Public Library

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Text Appearing Before Image: 238 WATER REPTILES OF THE PAST AND PRESENT row of large, median, supraneural elements render it quite certainthat there was a development of leathery hide comparable tothat of Dermochelys. The same may be said of Protostega gigas.But Archelon Marshii had a less reduced carapace, and the leatheryskin was probably less well developed; and Protostega Copei, inwhich no trace of supraneurals remains, must have made someapproach to the horn-shield condition. A more distinct suggestionof transition from the leathery to the horny shield covering may beseen in the very different contemporary Cretaceous form, Toxo-chelys Bauri, where ossified epi- or supraneurals occupy quite

Text Appearing After Image: Fig. 127.—Skull of Archelon ischyros: pa, parietal; /, frontal; pm, premaxilla;pf, prefrontal; ptf, postfrontal; m, maxilla,/, jugal; qj, quadratojugal; sur, surangu-lar; d, dentary; an, angular. (After Wieland.) exactly the nodal relation of the five vertebral horn shields of laterturtles, like Lytoloma, though there are not the slightest traces ofsulci. From a purely anatomical standpoint I have suggested thatArchelon had seven dorsal keels corresponding to those of Dermo-chelys. There is much excellent reason for regarding dermogeneossification as essentially double-layered throughout the Reptilia. In any restoration of Archelon ischyros only the mid-line shouldbe accentuated as a series of rather sharp supraneural crests. Theseare shown to have been present by the characteristic groove-likemedian pits with radiating striae, which are such a prominentfeature of epineurals. It is reasonable to believe that the pitsmark the attachment of horny crests developed in the leatheryhide.

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