e^i^';'r>^ 



JXJtULJlStSt . mlOl£_t.U«J-El-IIJ 



B 



TUttl LPJJi—l^ oust 



11 



Fig. 130. Stages in the Evolution of the Horse. 



(Left.) An ascending series of Oligocene three-toed horses {A, B, C), showing their evolu- 

 tion in size, form, and dental structure, which involved continuous change in thousands 

 of distinct characters and occupied a period of time estimated at 100,000 to 200,000 years. 



(Right.) Two Upper IMiocene American types of horses, Hipparion {F), with limbs pro- 

 portioned like those of the deer, representing the climax of the swift-moving, grassy 

 plains type, in contrast with Hypohippus {D, E), a conservative forest and browsing 

 type. This is an instance of the survival of an ancient browsing type in an ancient 

 forested environment {D, £), while in the adjacent grassy plains there exists contem- 

 poraneously the fleet Hipparion (F). 



Skeletons mounted in the American Museum of Natural History. Restoration under 

 the direction of the author, painted by Charles R. Knight. 



267 



