CIIELONIA 217 



cotylosaurs, which have no holes in the temporal roof of the skull, 

 and as the cotylosaurs were the most primitive and the oldest of 

 reptiles, this fact incontestably proves that the turtles had a very 

 ancient origin, though we know them no farther back than the 

 later Triassic. They are the only order of reptiles of which not 

 a single member is known to have teeth, or even vestiges of 

 them. Until recently only a single specimen has been known 

 from the Trias, and of that only the casts of the shell; but the 

 shell was as fully developed and as complete as that of a modern 

 alligator snapper, which it resembled much in form and in size. 

 And doubtless the habits of this ancient Proganochelys were similar 

 to those of the alligator snapper. The early cotylosaurian reptiles 

 were all littoral- or marsh-loving animals, and more or less aquatic, 

 and doubtless the early turtles continued in the same environments 

 and with the same habits after acquiring a shell for protection and 

 losing their teeth, which for some inexplicable reason they seemed 

 no longer to need. Until near the close of the Jurassic period 

 probably all turtles were amphibious animals of the marshes, 

 spending much, perhaps the larger part, of the time in the water, 

 good swimmers, and yet good crawlers. With the beginning of 

 the Cretaceous, however, some of them became ambitious for new 

 and untried modes of life. Various ones went down into the sea 

 and became marine animals, reaching the zenith of their prosperity 

 and the maximum of size before the close of the period, but con- 

 tinuing in diminished size and numbers to the present time, if 

 we may consider the leather-back turtle as really their descendant. 

 Others in the Cretaceous took to the rivers and ponds, and became 

 almost as thoroughly aquatic in their thin shape and soft covering; 

 and their lineal descendants still continue in the rivers of the 

 Northern Hemisphere. Still others, in the Age of Mammals, took 

 to the upland, and competed with the mammals in the open places 

 and prairies, reaching their maximum in Miocene-Pliocene times, 

 when for some unknown reason the giants among them were driven , 

 from the mainlands to continue a precarious existence to the present 

 time in some of the larger islands. 



Were there no turtles living we should look upon the fossil 

 forms as among the strangest of all vertebrate animals — animals 



