CHORDATA — VERTEBRATA — I\IA:M:MALS 



391 



Fig. 171. — Above: Typical scene in western North America during the Lower 

 Oligocene time, showing a small herd of titanotheres of the genus Brontotherium. 

 The individual in the foreground is a male. Below : A skeleton of a female 

 Brontotherium gigas from South Dakota. Note the small nasal horns in compari- 

 son with their tremendous development in the male above. (From Osborn.) 



