84 UNDERHILL : 



we have only the upper incisors retained, and these are con- 

 stantly growing and fully developed into tusks. 



As before mentioned, the forerunners of the Hoofed Ani- 

 mals, the Condylartha, of which the Phcnacodiis is the best 

 studied genus, have many carnivorous characters, and it is 

 difficult, among these earliest Eocene mammals, to differenti- 

 ate between the beginnings of the hoof-bearing and claw- 

 bearing groups. Specialization progressed during this period, 

 however, and before its close Ungulata and Carnivora had 

 become well defined both in America and Europe. The most 

 primitive Carnivora of the Eocene are usually placed in the 

 sub-order Creodonta, an extinct group of especial interest in 

 possessing characters almost identical with those of the Con- 

 dylartha. Their dentition differs from that of the true Car- 

 nivora in the complete absence of the carnassial tooth, or in 

 its development from other teeth of the series. In the modern 

 flesh eaters the carnassials are the fourth upper premolar and 

 the first lower true molar, which have high, strong crests, 

 working against each other and adapted for cutting. At the 

 beginning of the Mammalian Age the Creodonts are already 

 numerous, and, increasing in variety throughout the Eocene 

 period, seem to represent more than any other fossils thus far 

 discovered the central stem from which most all of our mod- 

 ern mammals have branched. But during the Eocene this 

 ancient stock became more and more crowded in the struggle 

 for existence by the increasing and more formidable true car- 

 nivores until by the close of that period they had gone down 

 under the law of survival and entirely disappeared. The 

 seven families of the living land Carnivora include the bears, 

 raccoons, dogs, civets, the mustelines, cats and hyccnas. Of 

 these the raccoons are peculiar to America, and the civets and 

 hyaenas are found only in the Old World, while the four 

 remaining families are found in all the continents except 

 Australia, in which continent Carnivora are not native. The 

 earliest known ancestors of these families were of a veiy gen- 

 eralized type, but most of the fossil true Carnivora can be 



