HISTORY OF THE CARNIVORA 



567 



all over the northern hemisphere, but it is not yet possible 

 to select from the crowd of allied genera those which formed 

 the actual steps of descent. These small animals were numer- 

 ous and varied and are far better known in North America 

 than in Europe and it is not at all improbable that some of 

 the lower Eocene genera migrated to the Old World and 

 there gave rise, among other forms, to ^Hycenodon and 



1 



^^"^, y 



^ ' -.1 V/ . 



""-*:!i>s/^.^<Ov-''^''" 



'?'^^'^^ i<M 



^v 



Fig. 281. - 



-tTritemnodon agilis, a primitive thyaenodont, Bridger stage. Restored 

 from a skeleton in the American Museum. 



fPterodon, which eventually returned to the land of their 

 earlier ancestry. If confirmed, this will be an exceptionally 

 interesting case of back and forth migration. However that 

 may be, the American Eocene genera, \Sinopa and ^Tritem- 

 nodon, illustrate very well the ancestry of the Oligocene genera, 

 as they must have been similar to the actual progenitors. 



The first and most obvious difference from the Oligocene 

 genera was the very much smaller size of the animals, few of 

 the Eocene forms equalling a fox in height. The teeth were 



