126 THE WHITE RIVER BADLANDS 



have ranged in great herds over the Oligocene and Mio- 

 cene lands of South Dakota, Nebraska, Colorado, Wyoming, 

 Montana and North Dakota. It is interesting in this con- 

 nection to note that the Oreodontidae, in addition to 

 giving their name to the Oreodon beds of the Middle Oligo- 

 cene furnished names also for three of the zones above the 

 Middle Oligocene, namely, the Laptauchenia zone, the 

 Promerychocrus zone, and the Merycochoerus zone. 



Leptauchenia was founded on fossil remains obtained by 

 Prof. Hayden in 1855 from near Eagle Nest butte. This ani- 

 mal is of interest in that its structure seems to indicate an 

 acquatic habit. (Plate 42). The teeth resemble somewhat 

 those of the llama (Auchenia) hence the name Leptauchenia. 

 Agriochoerus, is remarkable in that its toes were apparently 

 armed with claws instead of hoofs and the first toe (thumb) 

 of the fore foot seems to have been opposable. Aside from 

 its foot structure the animal was much like the Oreodon. 

 (Plate 42). It was approximately three feet long not includ- 

 ing the rather long tail. Mesoreodon is likewise remarkable 

 in that the thyroid cartilage of the larynx was ossified much 

 as in the howling monkey and according to Prof. Scott it 

 must have had most unusual powers of voice. 



Promerycochoerus, a larger and heavier animal than 

 those of the earlier genera, has been found in considerable 

 numbers in northwestern Nebraska and eastern Wyoming. 

 The restored skeleton of Promerycochoerus carrikeri is 

 more than five and one-half feet long and evidently indicates 

 a large bodied slow moving animal, the habits of which as 

 has been suggested were perhaps somewhat the same as 

 those of the hippopotamus. Peterson described the animal 

 briefly as having a massive head, a short, robust neck, dorsal 

 vertebrae, provided with prominent spines, lumbar vertebrae 

 heavy, thoracic cavity capacious, and the feet large. (Plate 

 38). 



The Oreodons are found in the Lower and Middle Oli- 

 gocene and are particularly common in what is known as 

 the "lower nodular layer" (red layer) of the Middle Oligo- 

 cene fifteen or twenty feet above the Titanotherium beds. 

 It is on account of the abundance of these fossils and their 

 early discovery in the Middle Oligocene that this division 

 of the badland formations was by Hayden given the name 

 of Oreodon beds. Leidy tells us that as early as 1869 he 



