THE COTYLOSAURIA 



S. W. WILLISTON 

 The University of Chicago 



The studies of Broili, and especially of Case, have furnished much 

 welcome information concerning the Permian reptiles of America 

 within recent years. But our knowledge of many of them is yet 

 meager, and much obscurity yet prevails as to their rank and affinities, 

 and especially as to their relationships with the known European and 

 African types. The ordinal name Cotylosauria has, within the past 

 few years, come into rather general use for many of the early stegocro- 

 taphous reptiles to the exclusion of other terms which had previously 

 been applied to them. A brief historical review of the origin and use 

 of the term will be of interest. 



Cope early introduced and made use of the term Theromorpha, 

 afterward changed to Theromera, to include many of the older 

 reptiles now recognized as quite diverse, and which he later so recog- 

 nized, abandoning it. In 1880^ he proposed the subordinal term 

 Cotylosauria for a division of this group, founded exclusively on the 

 Diadectidae of Texas, and based upon a real or apparent dicondylar 

 structure of the skull. Later, ^ he expressed doubt of its validity 

 as follows: 



I am still inclined to question whether the extraordinary characters of the 

 cranio-vertebral articulation I have described justify the separation of the Diadec- 

 tidae as a third suborder of the Theromorpha, which I have called the Cotylo- 

 sauria, or whether they are not due to the loss of a loosely articulated basioccipital 

 bone. 



The two other suborders of his Theromorpha to which he refers 

 were the Pelycosauria and Anomodontia — this latter of course in its 

 wide sense. In 1889^ he included in his order Theromera the follow- 

 ing six suborders : Placodontia, Proganosauria, Parasuchia, Anomo- 

 dontia, Pelycosauria and Cotylosauria. His Pelycosauria included 



1 American Naturalist, p. 334. 



2 Proceedings of the American Philosophical Society, 1882, p. 448. 



3 American Naturalist, p. 886. 



139 



