. Water reptiles of the past and present . e but a veryprimitive one at peculiarity con-sists in the absence ofany opening betweenthe ischium and pubis, which is characteristic of every living verte-brate with legs. And these and other old-fashioned characterscould not possibly have been new developments; they must haveexisted in all the ancestors of the Choristodera from Paleozoic toearly Tertiary times, though not a singleother reptile is known to have pos-sessed them, for the greater part ofthis time. Perhaps when Asia andnorthwestern America have been morethoroughly explored for
. Water reptiles of the past and present . e but a veryprimitive one at peculiarity con-sists in the absence ofany opening betweenthe ischium and pubis, which is characteristic of every living verte-brate with legs. And these and other old-fashioned characterscould not possibly have been new developments; they must haveexisted in all the ancestors of the Choristodera from Paleozoic toearly Tertiary times, though not a singleother reptile is known to have pos-sessed them, for the greater part ofthis time. Perhaps when Asia andnorthwestern America have been morethoroughly explored for vertebrate fos-sils, some of their ancestors which per-ished on their great migration from the peivic bones,western to the eastern continent inlate Cretaceous times will be discovered. The choristoderans began their existence, so far as is now known,in North America in late Cretaceous times and died out in bothEurope and North America, in early Tertiary times. That is, theywere one of the few branches of reptilian life which not only wit-. Fig. 91. Champsosauriis;(After Brown.) RHYNCHOCEPHALIA 183 nessed the extinction of the great dinosaurs and plesiosaurs, butthe advent also of the early placental mammals. They lived mil-lions of years after the proganosaurs became extinct, and, similaras they are in form, there is no relation between them. Moreover,in all probability they did not migrate to the eastern continent overthe same route. The structure of the head and teeth of the Choristodera clearlyindicates a fish-eating habit, or at least a diet of soft-bodied, free-swimming invertebrates. The legs and ribs, as also the armor ofventral ribs, like those of the plesiosaurs, point very insistentlytoward a bottom-crawling habit while in the water. CHAPTER XIVPARASUCHIA The first known specimen of the order of reptiles now generallyknown as the Parasuchia was found in Wiirtemberg, Germany, in1826 and very briefly and inadequately described1 two years laterby Professor George Jaeger.
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