182 WATER REPTILES OF THE PAST AND PRESENT 



Brown.) 



the atlas, had changed but little from that of their very ancient 



forbears of Permian times, and the bones of the palate still retained 



numerous teeth scattered over it, like those of the same Paleozoic 



ancestors. Most primitive and old fashioned of all was the pelvis, 



which was so unlike that of all known contemporary or later 



reptiles that, were a 



paleontologist to see 



it without knowing 



whence it came, he 



would be almost sure 



to say that it belonged 



to a Paleozoic, or at 



least a Triassic, reptile, 



and not only to an 



early reptile but a very 



primitive one at that. 



This peculiarity con- 

 Fig. 90.- -Pectoral girdle of Champsosaurus. (After gists Jn the absence f 



any opening between 

 the ischium and pubis, which is characteristic of every living verte- 

 brate with legs. And these and other old-fashioned characters 

 could not possibly have been new developments; they must have 

 existed in all the ancestors of the Choristodera from Paleozoic to 

 early Tertiary times, though not a single 

 other reptile is known to have pos- 

 sessed them, for the greater part of 

 this time. Perhaps when Asia and 

 northwestern America have been more 

 thoroughly explored for vertebrate fos- 

 sils, some of their ancestors which per- _ „. 



^ Fig. 91. — Champsosaurus; 



ished on their great migration from the pe ivic bones. (After Brown.) 

 western to the eastern continent in 

 late 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 both 

 Europe and North America in early Tertiary times. That is, they 

 were one of the few branches of reptilian life which not only wit- 



