230 GEOLOGY. 



The main herbivorous line. — While the condylarths and creodonts 

 were structurally near one another at the opening of the period, it was 

 not long before a clear distinction arose between their respective deriv- 

 atives, the hoofed herbivores (ungulata) and the clawed carnivores (un- 

 guiculata). The condylarths were small generalized forms with five 

 toes and forty-four teeth, not yet developed into the true herbivorous 

 type, but displaying differentiation in that direction. The accompany- 

 ing figure shows the general features of the skeleton of one of the best- 



Fig. 427. — A primitive ungulate or condylarth from the second Eocene epoch 

 (Wasatch) Phenacodus primcevus Cope, about T V natural size (about the size of a 

 tapir), from Big Horn basin, Wyoming. (After Cope.) 



known genera (Phenacodus). Without radical change, the condylarths 

 have lived on till the present time, but a branch seems to have di- 

 verged early, and to have deployed rapidly into the ungulates. This 

 branch seems to have consisted of small five-toed forms adapted to for- 

 ests and marshes where succulent vegetation afforded an easy sustenance. 

 In the course of the period many of them became gradually fitted for 

 life on the grassy plains. To this end, hard hoofs and powerful grinding 

 teeth, capable of masticating coarse, dry herbage, were developed. The 

 canine teeth gradually disappeared, and the molar and pre-molar teeth 

 assumed flat, corrugated crowns seated on well-developed roots. The 

 frontal teeth were variously adapted to cropping vegetation. In the 

 foot there was a progressive abandonment of the flat heavy palmate 



