File:Image from page 246 of "Water reptiles of the past and present" (1914) (14750104566).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: and.) About a half-dozen species and two genera of the family haveso far been described, all coming from the Upper Cretaceousdeposit of Kansas and South Dakota, the genus Archelon from laterrocks than those which have yielded Protostega. The general form and structure of Archelon will best be under-stood from the accompanying figures after Wieland (Figs. 123,124, 125) and the restoration of the living animal as interpretedby the writer (Fig. 126). If the leather-back turtle, described CHELONIA 235 farther on, is really the descendant of these or allied turtles, as many-authors believe, it of course represents the very highest aquaticspecialization of all Chelonians. If, on the other hand, as somebelieve, the leather-back is the end of a long and independent lineof descent, then Archelon represents the highest aquatic specializa-tion of all other turtles. In size, at least, Archelon attained the maximum of the order,reaching a length of more than twelve feet, and a weight of more ^S^ ^

Text Appearing After Image: Fig. 124.—Archelon from below, without plastron: h, humerus; r, radius; u, ulna;sc, scapula; c, coracoid; p, pubis; i, ischium. (From Wieland.) than three tons. Except that the shell was not heart-shaped orelongated as in all modern sea-turtles, but nearly circular in out-line, it had all the aquatic adaptations of the sea-turtle in a yethigher degree. The shell was depressed; the dermal plates covering the ribshad almost entirely disappeared, remnants only of their upperends remaining; the skull (Fig. 127) had the temporal regionwholly roofed over; the neck was short and not retractile. The 236 WATER REPTILES OF THE PAST AND PRESENT front legs were strong flippers, the humerus was long and stout,with the crest for the attachment of muscles far down on theshaft; the digits were greatly elongated and clawless, etc. Theplastron only was less reduced than in the case of the modern sea-turtles. No traces of horny shields have been discovered. As tothe nature of the covering and the gene

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