

ANIMALS OF THE PAST 339 



tusks, necessitated the development of a prehensile upper lip 

 which gradually evolved into a proboscis for food gathering. 

 The elongation of the lower jaw implies a similar elongation 

 of this proboscis in order that the latter may reach beyond 

 the tusks. The trunk did not, however, reach maximum 

 utility until the shortening jaw, removing the support 

 from beneath, left it pendant as in the living elephant. 

 The change in the form of the skull developed pari passu 

 with the growth of the tusks and trunk as it is merely a 

 mechanical adaptation to give greater leverage in the 

 wielding of these organs. It may readily be seen that these 

 changes curiously interact upon one another; the result of 

 the evolution of its parts being the development of a most 

 marvelous whole." 



Though elephants passed most of their evolutionary 

 history in Africa, America can claim the distinction of 

 having been the chief field for the evolution of horses. 

 Lull says: " These horse-like animals, to which the name of 

 hyracotheres has been given ranged throughout the entire 

 Eocene period. They were of small size ranging upward 

 from eleven to fourteen inches at the shoulder. The hand 

 bore four digits, while in the foot but three out of the 

 primal five remained. Hyracotherium itself, the oldest of 

 its race, is known from a skull found in the London Clay, 

 while both in England and America is found the widespread 

 Dawn Horse, Eohippus. The scene of the evolutionary 

 drama being shifted to our land, we find Eohippus (Fig. 

 114, F) succeeded by the somewhat larger Orohippus, the 

 mountain horse (G), while Epihippus carries the race close 

 to the close of Eocene time, a duration of at least two million 

 years." During the Oligocene lived Anchiiherium with three 

 functional toes on each of its feet; the speedy Mesohippus 

 (H) was eighteen inches in height at the withers; and its 

 successor, Miohippus (I), stood twenty-four inches high. 

 "The Miocene period was the millenium of mammals, and 

 this was superlatively true of the horses." Though three- 

 toed horses lived in the early part of this period, they were 



