MIOCENE AND PLIOCENE HORSES 
which its short simple teeth sufficed. This horse lived under 
the favorable conditions of the Upper Miocene period, when 
this country had an almost tropical climate, vegetation was 
luxuriant, and the continent teemed with fine animals, great 
and small, as did Africa and India a century ago. 
With it lived the ‘‘deer horse” (Neohipparion), which was 
‘proportioned like the Virginia deer, — delicate and extremely 
en Ge ee OL 
By permission of the American Museum of Natural History. 
EOCENE FOUR-TOED HorsE (Protorohippus). 
Restoration by Charles R. Knight, under direction of Professor H. F. Osborn. 
fleet-footed, surpassing the most highly bred modern race horse 
in its speed mechanism.’ Nevertheless both races became 
extinct and left no visible progeny. Protohippus was succeeded 
in the Pliocene by Pliohippus, about the size of a Shetland 
pony, in which the side toes no longer come near the ground; 
and this is confidently regarded as the lineal American ancestor 
of the modern horse, though the fossil connection is not yet 
complete. These Miocene and Pliocene horses were probably 
striped, like zebras, while the earlier, forest-running sorts were 
355 
