316 LAND MAMMALS IN THE WESTERN HEMISPHERE 



With the Wind River the history of the ftitanotheres breaks 

 off short, and from present information, can be carried no 

 farther back. Possibly, there was a Wasatch ancestor, which 

 only awaits discovery, but it seems more likely that these 

 earliest known genera were belated immigrants from the same 

 as yet unknown region, whence came the modernized and pro- 

 gressive elements of the Wasatch fauna. Except for its ob- 

 scure beginning, the family was pre-eminently characteristic 

 of North America, and only two representatives of it have been 

 found outside of that continent, one in Hungary and one in 

 Bulgaria. No doubt others will yet be found in Asia. 



Both in its resemblances and its differences, as compared 

 with the far longer and more complex story of the horses, the 

 history of the ftitanotheres has instructive bearings upon 

 evolutionary theory. 



(1) Starting with two phyla, one of which speedily died 

 out, the other ramified into four or five, which continued until 

 the disastrous end, pursuing a nearly parallel course of develop- 

 ment. 



(2) There was a great increase in size and especially in bulk 

 and massiveness from species no bigger than a sheep in the 

 Wind River stage to those which rivalled small elephants in 

 the lower White River. 



(3) The teeth underwent comparatively little change ; the 

 incisors dwindled and lost functional importance and the ca- 

 nines were reduced, horn-like growths taking their place as 

 weapons; the premolars grew larger and more compUcated, 

 but never attained the full size and complexity of the molars, 

 as they did in other perissodactyl families. 



(4) Horn-like, bony protuberances appeared first as small 

 humps and knobs over the eyes and steadily enlarged, at the 

 same time shifting their position forward, until they finally 

 attained great size and were on the nose. 



(5) The skull was modified so as to support these weapons 

 and endure the shock of impact when they were put to use. 



