90 THE WHITE RIVER BADLANDS 



St eneo fiber fossor in close association with the Devil's Cork- 

 screws of the Harrison beds and, as referred to elsewhere, 

 suggests the reason for the association. This animal was 

 smaller generally than the present day beaver. Its skull is 

 comparatively large, the lower jaws heavy, neck short, limbs 

 and feet powerful, tail round, rather heavy and of moderate 

 length. Peterson states that the limb presents a striking 

 similiarity to that of other burrowing rodents and ap- 

 proaches that of the mole in its position. The elongated and 

 narrow scapula of the mole, the heavy clavicle, the strongly 

 built humerus, and the broad foot with the long and power- 

 ful unguals, is rather suggestive of the habits of this animal, 

 which was probably burrowing to a considerable degree. The 

 animal is related to the beaver, but is evidently not in the 

 direct line of ancestry. 



UNGULATES 



The order Ungulata (Herbivores) as now constituted in- 

 cludes the mammals once loosely classed as Kuminants, and 

 Pachyderms. The earliest known forms much resemble the 

 primitive Carnivores. The ancestors of both seem to have 

 been omnivorous. 



For some reason there appeared very early among the 

 Ungulates a tendency to develop the herbivorous type of 

 tooth and the digitigrade foot (walking upon the tips of the 

 toes ) . The change in the foot from the five toed plantigrade 

 form progressed along two different lines and thus there 

 were produced two very different types, ,namely, the odd-toed 

 type and the even-toed type. In the odd-toed type the axis 

 of the foot is in the third or middle digit (mesaxonic). 

 Animals of this type are known as Perissodactyls. In the 

 even-toed types the axis of the foot is between the third and 

 fourth digits (paraxonic). Animals of this type are known 

 as Artiodactyls. The horse, the tapir, and the rhinoceros 

 are well known representatives of the perissodactyls. Among 

 Artiodactyls are the camel, lama, deer, giraffe, antelope, ox, 

 sheep, goat, and bison. 



PEKISSODACTYLS 



Perissodactyls, as above stated, have the axis of the foot 

 in the third or middle digit. They are generally odd toed, 

 the third toe being the largest and sometimes the only func- 



