INTRODUCTION 



THE PRIMITIVE SKELETON OF REPTILES 



That the reptiles were evolved from the Amphibia, and more spe- 

 cifically from that order known as the Temnospondyli, seems now 

 assured. The earliest as also the most primitive reptiles that we 

 know belong to the order called the Cotylosauria. With the excep- 

 tion of Eosauravus from the middle Pennsylvanian of Ohio, of which, 

 unfortunately, the skull is unknown, our knowledge of them goes no 

 further back than the late Carboniferous and early Permian. At 

 that time there was a considerable diversity of known forms, belong- 

 ing to at least four well-differentiated groups and twenty or more 

 families; from which we may very properly conclude that their earli- 

 est ancestors, the beginning of their stock, lived much earlier, cer- 

 tainly at the beginning of the Upper Carboniferous, and very prob- 

 ably in Lower Carboniferous times. We therefore never can expect 

 to find in the rocks of the Permian any real connecting link between 

 the two classes. 



Both the reptiles and the amphibians had changed in this interval, 

 an interval perhaps of millions of years, retaining in varying degrees 

 their ancestral characters, while losing or adding others in various 

 ways. The reptiles, by the acquirement of a new mode of life, the 

 loss of gills in their youth and entire emancipation from the water, 

 became more progressive than the amphibians, and their evolution 

 was more rapid. Characters that are common to many amphibians 

 became more and more rare among the reptiles, and the amphibians, 

 handicapped by inherited habits, were restricted more and more to 

 subordinate roles, and only a few of the more progressive continued 

 to develop. They, for the most part, lost those characters and adap- 

 tations that brought them into immediate competition with the rep- 

 tiles, and by the close of Triassic times had become restricted to 

 habits and habitats no longer invaded by them. The modern toads, 

 frogs, salamanders, and blindworms differ far more from the higher 

 amphibians of Paleozoic times than did the latter from their con- 

 temporary reptiles. 



