226 GEOLOGY. 



beaver (Pal&caster Nebrascensis) , was also abundant at this time. 

 The squirrels of that time were large, as is indicated by the remains 

 of Ischyromys typus, whose' head was larger than that of a musk- 

 rat. The rabbit of the Nebraska Miocene was smaller than the 

 common species of the State at the present time 



The horse family (Solidunguld), which is now represented by one 

 genus (Equus), whose characteristic species are the horse and the 

 ass, was rich in genera and species during the Miocene. We have 

 already seen that the family came into being in the early Eocene, 

 the first known characteristic form being the Eohippus. In the 

 early Miocene we already have the Mesohippus, represented by 

 several species whose distinctive peculiarity was that the fourth toe 

 had become a rudimentary useless splint. Next in the Miocene 

 came the Anchitheriums, which were represented in Nebraska by 

 one species, with three additional forms in Colorado. The peculiar 

 feature of these horses was that they had three toes, all of which 

 touched the ground, the two lateral, Jiowever, being comparative- 

 ly small and weak. Closely allied to these were the Hyperions, 

 several species of which lived during Nebraska Miocene times. 

 They also had three toes, but only the middle one touched the 

 ground, the two lateral swinging not much unlike the two side 

 toes of the hog, being, however, comparatively much smaller. 

 Another genus, Merychippus, was closely related to the preceding. 

 These Miocene horses ranged in size from an animal much smaller 

 than the ass to animals about the size of a small modern horse. It 

 is seen, therefore, that at least four genera of horses existed in Mio- 

 cene times, each genus, however, being represented by from one 

 to several species. They must have been exceedingly numerous, 

 and doubtless roamed over our plains in countless numbers. 



Another peculiar family of odd-toed animals that existed in Mio- 

 cene times were the Titanotheriums. Leidy first described and 

 named them. So abundant are their remains at one horizon in the 

 lower Miocene that it has given it the name of Titanotherium bed. 

 Marsh afterwards described a closely related animal by the name of 

 Brontotherium. Subsequently Cope described another of the same 

 family by the name ofSymborodon. Megaceratops Coloradoensis, 

 of Leidy, belongs to the same group. These animals had the same 

 bulk of body of the elephants, and united the characters of the rhi- 

 noceros and elephants with more distant affinities to the Dinocer- 

 ata of the Eocene. The head was extremely elongated, and be 



