CONCLUSION. 



The order Cotylosauria, as defined in this paper, includes all the primitive 

 reptiles with a complete roof over the temporal region of the skull, single-headed ribs, 

 and the neural arches of the vertebrae broad and low, with swollen sides and short 

 spines. It has become increasingly apparent during these studies that the order 

 Cotylosauria, as defined by Cope, was very far from occupying the primitive position 

 assigned to it by him. The forms on which he based the order, now confined to 

 the suborder Diadectosauria, can only be considered as a very specialized branch of 

 the primitive stem. 



The order originated as early as middle Pennsylvanian time (Eosauravus 

 Case and Sauravus Thevinin) and spread over the world. By upper Pennsylvanian 

 time widely different suborders were established in North America, in Pennsylva- 

 nia (18), and perhaps Texas (17); in the Permian other suborders were established 

 in Germany, South Africa, and Northern Russia and a little later, in the Trias, they 

 had spread to Scotland and over Central Europe. The wide distribution of the 

 order in middle Permian time indicates very clearly its much earlier origin, unless 

 we resort to the improbable assumption of a diphyletic origin. 



It is impossible to point with any degree of confidence to the place of origin of the 

 order. Eosauravus, from the beds of Alleghany age in Linton, Ohio, is the oldest- 

 known reptile, but Sauravus of France is nearly as old. The Cotylosauria of North 

 America were of Pennsylvania or lower Permian age. A consideration of the follow- 

 ing table makes it apparent that most of those of the Old World were a little younger. 



Name. Loulitjr. Geological Horizon 



PareiasauTus South Africa Pareiasaurus Beds, Beaufort, Middle Permian. 



Antkodon South Africa Pareiasaurus Beds, Beaufort, Middle Permian. 



Propappus South Africa Endothiodon Beds, Beaufort, Upper Permian. 



Procolophon South Africa Procolophon Beds, Beaufort, Middle Trias. 



Thelegnathus South Africa Cynognathus Beds, Beaufort, Middle Trias. 



SauTosternon South Africa Endothiodon Beds, Beaufort, Upper Permian. 



PauiasauTus Russia Dwyna River, Upper Permian. 



Elginia Scotland Gordonia Beds, Bunter, Lower Trias. 



TeUrpeton Scotland Sugonolepis Beds, Keuper, Upper Trias. 



SclerosauTus Germany Ruhen near Basel, Upper Bunter, Lower Trias. 



PhanerosauTus Germany, near Zwickau . . Rothliegende, Middle Permian. 



Suphanospondylus Germany Rothliegende, Middle Permian. 



Sauravus France Upper Stephanien. 



This does not establish the origin of the group in North America, however, as 

 Sauravus indicates their early presence in Europe. One thing is certain, the Coty- 

 losauria of North America were isolated from the Old World during the Permian 

 and developed types peculiar to the continent; whether they gained access to Europe 

 in the Triassic is uncertain. The Pelycosauria, which developed with the Cotylo- 

 sauria, migrated as far as Bohemia in the Permian and existed in Europe after they 

 had died in America. This has not been shown conclusively for the Cotylosauria, 

 though evidence of certain foreign forms brought out in this paper point to the same 

 thing. It is possible that the group, indigenous to America, became extinct there, 



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