CHORDATA — VERTEBRATA — MAMMALS 



385 



especially during the Oligocene, Miocene and Pliocene, there 

 is a reduction in the number of browsing and ambulatory ani- 

 mals and an increase in the grazing and cursorial types. The 



Fig. 166. — A primitive light-limbed, omnivorous, hoofed mammal. Phenacodus 

 primcevus Cope, one of the Condylarthra, from the Wasatch (Lower Eocene) of 

 Wyoming. This animal, somewhat larger than a sheep, was in this case excep- 

 tionally well preserved. It is shown here, laterally crushed, just as it occurred in 

 the rocks, ca., carpal (wrist) bones; ca/. , calcaneum ; fe., femur; fi., fibula; 

 hu., humerus; il., ilium; m.ca., metacarpal (palm) bones; m.ta., metatarsals; 

 ob., orbit of eye; pa., patella; ph., phalanges (toes); ra., radius; s., scapula; 

 ta., tarsal bones; ti., tibia ; uL, ulna; /, //, ///, IV, V, digits, ist (corresponding 

 to thumb and great toe), 2d, etc. (After Cope.) 



principal advance in the mammals lay, however, in the enlarge- 

 ment of the brain (Fig. 162). 



The Ungulata include the following ten sub-orders : — 

 (i) The most primitive of the Ungulata are the extinct Con- 

 dylarthra (Eocene), difficult of separation from the early Car- 

 nivora, — the Creodonta. They are light-limbed animals 

 with a small brain and usually with forty-four short-crowned 

 and tuberculate teeth. The best-known example is Phenacodus 

 from the Lower Eocene (Figs. 165, 166). 



(2) The Hyracoidea (Lower Oligocene to present) are probably 

 but slightly modified descendants of the Condylarthra; these 



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