CREATION BY EVOLUTION 



America, however, they flourished, and they continued to 

 multiply and to grow larger during the following epoch, the 

 Oligocene. 



The Oligocene horses were larger than their predecessors, 

 and each of their feet bore three toes. This three-toed horse 

 is called Mesohippus. It appears to have been confined to 

 the American continent, a fact suggesting the temporary sev- 

 erance of land connection between North America and Asia. 

 The later Oligocene horses (M/ob/ppus) were larger and 

 had longer teeth and smaller side toes than the earlier forms. 



During the Miocene epoch, which followed the Oligocene, 

 Western North America was inhabited by many kinds of 

 horses, among them one that has been called the "forest 

 horse." The Miocene horses were also three toed and had 

 low-crowned teeth. The forest horses spread from America 

 to Asia and Europe, where their remains are found ; but they 

 appear to have died out in America in mid-Miocene time 

 and later in Europe. The main line of the horses, however, 

 continued to exist and underwent great changes, all originat- 

 ing in America. These changes appear to have been deter- 

 mined by environment. The teeth became longer and harder 

 to adapt them better to grazing; the feet, which in the earlier 

 horses were first five-toed, then four-toed, and then three- 

 toed, advanced toward a single-toed form, the side toes 

 becoming useless (Fig. 2). These changes indicate growing 

 adaptation to life on grassy plains. The grass of these plains 

 is harsher than that in or near forests, containing more silica, 

 and horses that feed on it must have hard teeth. A hard, 

 small hoof is also peculiar to plains horses, as well as long 

 legs, for the horse must be able to escape from enemies, such 

 as wolves and other carnivorous animals. 



In their adaptation to life on plains in Miocene time the 

 horses differentiated into three groups, the types of which 



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