30 EVOLUTION OF THE HORSE 



Parallel Evolution in (3ther Races. 



It is interesting to observe that while the evolution of the 

 Horse was progressing during the Tertiary period in North 

 America another group of hoofed animals, the Litopterna, now 

 extinct, in South America evoh'ed a race adapted to the broad 

 plains of Argentina and Patagonia and singularly like the Horse 

 in many ways (see exhibit in A-case in centre of hall). These 

 animals likewise lost the lateral toes one after another, and con- 

 centrated the step on the central toe ; they also changed the form 

 of the joint-surfaces from ball-and-socket to pulley-wheel joints; 

 they also lengthened the limbs and the neck; and they also 

 lengthened the teeth, and complicated their pattern. Unlike the 

 true Horse, they did not form cement on the tooth, so that it was 

 by no means so efficient a grinder. This group of animals native 

 to South America became totally extinct, and were succeeded by 

 the horses, immigrants from North America, which in their turn 

 became extinct before the appearance of civilized man. 



Many of the contemporaries of the Horse in the northern 

 hemisphere were likewise lengthening the limbs, lightening and 

 strengthening the feet, elongating the tooth-crowns to adapt 

 themselves to the changing conditions around them, but none 

 paralleled the Horse Evolution quite so closely as did the pseudo- 

 horses of South America. But the camels in America, the deer, 

 antelope, sheep and cattle in the Old World progressed on much 

 the same lines of evolution, although their adaptation was not to 

 just the same conditions of life. 



