SUCCESSIVE MAMMALIAN FAUNAS 273 



Bridger perissodactyls had four toes in the front foot and three 

 in the hind, while in the White River beds above the lowest 

 substage the number three in both fore and hind feet was 

 almost equally universal. 



One of the most radical and striking differences between 

 the Uinta and Bridger faunas was the rarity of Artiodactyla 

 in the latter, which is in almost equally strong contrast with 

 their abundance in the middle Eocene of Europe. Most 

 significant of these rare Bridger artiodactyls were the little 

 creatures (^Homacodon), hardly so large as a domestic cat, 

 which may fairly be regarded as a very early stage, if not the 

 actual beginning, of the great camel family, which was destined 

 to play so conspicuous a part in the life of America, North 

 and South. Small pig-like animals {^Helohyus) which were 

 no doubt ancestral to the peccaries, were fairly common and 

 there were, in addition, relatively large animals i^AchcFnodon) 

 allied, but not ancestral, to the fgiant-pigs of the Oligocene ; 

 some of these were considerably larger than a full-grown Wild 

 Boar {Sus scrofa). 



Among all the many hoofed mammals of the Uinta and 

 Bridger there was not a single one that had the high-crowned, 

 persistently growing teeth of the grazers ; all of them must have 

 had browsing habits and have fed upon such soft vegetable 

 tissue as did not rapidly abrade the teeth. The same state- 

 ment applies, d fortiori, to the stages antecedent to the Bridger 

 and therefore to the entire Eocene and Paleocene. From these 

 facts it may be inferred that the grasses had not yet taken 

 possession of wide areas. Concerning the Bridger fauna. 

 Professor Osborn, who has done so much to elucidate it, says : 

 ''On the whole, it is a very imposing, diversified and well- 

 balanced fauna, with an equal distribution of arboreal, cur- 

 sorial, aquatic, fossorial, carnivorous and herbivorous types." 



The lower Eocene is divisible into two stages, in descending 

 order, the Wind River and Wasatch, both extensively exposed 

 in central Wyoming. As would be expected from its strati- 



