LIFE 



567 



cxistrd then. In general, the mammalian faunas of the Eocene 

 of North America were closely similar to those of western Europe, 

 \\hiU- during the Middle and Late Eocene there seems to have 

 been faunal separation between these continents. 1 



Main herbivore line. While the condylarths and creodonts 

 were near each other at the beginning of the period, the hoofed 

 herbivores and the clawed carnivores developed from them soon 

 became distinct. The condylarths (Fig. 476) were small generalized 



Fig. 476. A primitive ungulate or condylarth of the Wasatch epoch; Phenaco- 

 dtis primiK'u* : Tcipe. about 1/13 natural size (about the size of a tapir), from Big 

 Horn basin, Wyoming. (Cope.) 



forms with five toes and forty-four teeth, not yet developed into true 

 herbivores. Condylarths did not live beyond the Eocene, but one 

 branch adapted to forests and marshes seems to have diverged early, 

 and perhaps to have given rise later to the ungulates. In the course 

 of the period many of them became fitted for life on grassy plains. 

 To this end, the flat, heavy, palmate form of foot adapted to marshes, 

 gave place gradually to the light, springy, digitate form, adapted to 

 a quick start and swift flight. At the same time hard hoofs, and 

 grinding teeth were developed. The evolution of hoofs and grind- 

 ing teeth has been thought to be connected with the prevalence of 

 grassy plains, the firm turf of which is in contrast with the soft soil 

 1 For references to important literature on the American Tertiary Mammalia, 

 see the authors' larger work, Vol. Ill, p. 228. See also Osborn, Bull. 361, U. S. 

 Geol. Surv., and The Age of Mammals; and Scott, A History of Land Mam- 

 mals in the Western Hemisphere. 



