94 THE WHITE RIVER BADLANDS 



that of Metamynodon planifrons in the American Museum of 

 Natural History, measures nine and one-half feet long and 

 four and one-half feet high at the shoulders. The true rhin- 

 oceroses began as light limbed, hornless animals, interme- 

 diate in proportion between the two just mentioned, and in 

 size and structure were not greatly unlike modern tapirs. 

 During much of their early life history they, like the more 

 primitive Hyracodonts and Amynodonts, were entirely with- 

 out horns. 



Figure 37 — Skeleton of the heavy, marsh loving Oligocene rhinoceros, 

 Metamynodon planifrons. Osborn, 1898. 



The true rhinoceroses constitute in many respects the 

 most important of the three subdivisions and to the paleonto- 

 logist are of profound interest. They lived in great num- 

 bers in the region of the Black Hills during Oligocene and 

 Miocene time, and their skeletons in certain favored local- 

 ities, particularly in the Big Badlands and in Sioux County, 

 northwestern Nebraska, have been collected in abundance. 

 The Oligocene forms are especially characterized as being 

 without horns, hence the old name Acerathere. ( Plate 15 ) . 

 The Miocene forms have generally, but not always, a rudi- 

 mentary or fairly 'well developed pair of horns placed 

 transversely across the anterior part of the head, hence 

 the name Dicerathere. (Plate 26). Present day rhino- 

 ceroses, it should be remembered, have either no horn or 

 one or two horns, but the arrangement when horns are 

 present is always medial, never transverse. It is of in- 



