116 A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



Still it would occasion no surprise to find American Cotylosaurs in the European 

 deposits of Permian age or younger ; for if such specialized types as Naosaurus 

 could migrate from Texas to Bohemia, even such slow-moving forms as Diadectes 

 and Captorhinus could do the same. 



As in the case of the Pelycosauria, it is probable that the Cotylosauria endured 

 longer in the Old World than the new. They occur through the Permian and into 

 the Triassic. Specialization did not progress so far in America as in Europe, for 

 we have in Chilonyx only the beginning of the development of prominent tubercles 

 and spines in the skull, such as marks the extreme types, Elginia from the Trias of 

 Scotland and Pareiasaurus from the Upper Permian of North Russia. Moreover, 

 there is no cenainty of any defensive dorsal armor in the American Cotylosauria, 

 while it was well developed in the European and African forms. The peculiar 

 development and posterior inclination of the incisor teeth in Labidosaurus and Cap- 

 torhinus is also not found outside of North America. 



Broom (lOa) has recently expressed the idea that there is a distinct genetic 

 relationship between the American and South African Permian reptiles. He con- 

 siders that the groups had a common origin somewhere in the northern part of South 

 America, and from there spread to North America and were there isolated, and later 

 to South Africa across the Antarctic Continent. He says: 



"Taking all the facts into consideration, it seems to me probable that in Upper 

 Carboniferous times there appeared in the northern part of South America a primi- 

 tive land vertebrate fauna comprising, among other types, temnospondylous am- 

 phibians, primitive Cotylosaurians, and primitive ancestral Pelycosaurs. Before 

 the conclusion of the Carboniferous period this South American fauna invaded 

 North America and almost immediately afterwards the northern group became 

 isolated. The isolation continued during at least the whole of the Lower Permian 

 time, and these isolated types became greatly specialized in their struggle with some 

 adverse conditions. What the conditions were, we do not know; and no satisfac- 

 tory explanation has, I think, been given of the development of the enormous spines 

 of the vertebrae in the Pelycosaurs. Nor do we know what caused the extinction 

 of the whole fauna about Middle Permian times, but most likely some change in 

 climatic conditions. 



"In South Africa the first Karroo reptile to appear is Mesosaurus, which is 

 found in beds a little above the Dwyka tillite. It is certainly generically similar to the 

 Mesosaurus of Brazil and closely allied specifically This occurrence of Mesosaurus 

 on both sides of the Atlantic, as well as a series of plants which are specifically 

 identical in Brazil and South Africa, renders it practically certain that there was a 

 land connection between South America and South Africa in Lower Permian times, 

 and that animals might have migrated from what is now the one continent to the 

 other. There is, however, no evidence that any reptiles other than Mesosaurus 

 arrived in South Africa till some considerable time after the origin of the Permian. 

 Perhaps the reason for this may be that about the beginning of the Permian period 

 South Africa and probably much of South America, Australia, and India was, from 

 some cause or other, largely covered by glaciers, and possibly for long afterwards the 

 climate was too severe to allow the more northern or equatorial types to invade the 

 south. In beds which are called Ecca we get the earliest immigrants — a large car- 

 nivorous reptile called Archccosuchus, which may have been a Dinocephalian, and 

 evidence from a tooth of a large undoubted Dinocephalian which was a herbivore. 

 It is, however, not till Middle Permian times that the fauna becomes rich. Then 



