. Water reptiles of the past and present . 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 a
. Water reptiles of the past and present . 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 general appearance of the. Fig. 125.—Archelon; skeleton from below: hy, hyoplastron; hpp, hypoplastron.(From Wieland.) turtle when alive, Dr. Wieland has kindly given the writer hisviews, as follows: After direct study or fairly close examination of all the fossilmaterial of importance thus far collected representing the Pro-tostegidae, it seems certain that in all the members of the groupan external leathery layer was well developed. In no instance isthere the slightest trace of horny shield sulci, or grooves; thoughit seems probable that there was some gradation toward a thin andperhaps even slightly horny hide. In Archelon ischyros the re-duced condition of the carapace and the presence of the continuous CHELONIA 237
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