Structure mid Affinities of the Endothiodont Beptilcs. 279 



the Dicynodontidse, and the other Anomodonts, which have molars, 

 in a separate family — the Endothiodontidse. 



With regard to the origin of the Endothiodonts little is known. 

 There is no doubt that there is some affinity between the Anomo- 

 donts and the Theriodonts, and though neither can be descended 

 from the other, both doubtless had a common ancestor. There is 

 strong probability that this common ancestor was one of the Thero- 

 cephalians, but at present unknown. The cranial characters are 

 strikingly similar in the Anomodonts and Therocephalians, and the 

 other skeletal characters also point to a close relationship. When a 

 Therocephalian is discovered which shows a degeneration of the 

 incisor teeth we shall probably have a form allied to the ancestor 

 of the Anomodonts. 



The known Endothiodonts may be arranged phylogenetically 

 thus : — 



Therocephalian Ancestor 



Cryptocynodon, Seeley 

 Esoterodon, Seeley 



Prodicynodon, Broom 



Chelyoposaurus, Broom 



Dicynodon, Owen 



Endothiodon, Owen 



Pristerodon, Huxley 



Opisthoctenodon, Broom 



Oudenodon, Owen 

 Lystrosaurus, Cope Kistecephalus, Owen 



