South Dakota School of Mines 77 



CREODONTA. 



The Creodonts were particularly abundant and well dif- 

 ferentiated in the earliest American Tertiary. They were evi- 

 dently the predatory flesh eaters of that time, occupying much 

 the position relative to other animals that the true carnivores 

 have held since the extinction of these their more primitive 

 ancestors. Of all their numerous families only two or three so 

 far as known survived the Eocene and continued into the 

 Oligocene. One of these, the Hyaenodontidae, the latest and 

 most specialized, is found in South Dakota and neighboring 

 states. The individual fossils are not abundant here although 

 several species are represented. Professor W. B. Scott of 

 Princeto'n University who has written a very full account of 

 the Osteology of Hyaenodon tabulates the following:* 



Hyaenodon. crucians Leidy 

 Hyaenodon cruentus Leidy 

 Hyaenodon horridus Leidy 

 Hyaenodon leptocephalus Scott 

 Hyaenodon mustelinus Scott ■ 

 Hyaenodon paucidens Osborn and Wormian. 



These are all from the Middle Oligocene. Some poorly 

 preserved remains have been found in the Lower Oligocene, but 

 little is known of these except that, like the Middle Oligocene 

 species, they belong to the genus Hyaenodon. The size of the 

 individuals varies considerably but the specific differences are 

 not great. According to Scott there is much constancy in the 

 more important structures. 



The skull of the largest, Hyaenodon horridus, according 1 

 to Leidy, reached the size of that of the largest black bear, 

 Ursus americanus, but, as pointed out by Scott, the head of the 

 animal appears large out of all proportion to body and iimbs. 

 It is quite different in shape from that of any of the true car- 

 nivores, due in large measure to the length of the cranial region 

 with its very lofty sagittal crest and to the extreme straightness 

 and slenderness of the zygomatic arches, the position of which 

 is very low down on the sides of the skull. In general the brain 

 case is small. Other characteristic features are the great length 

 of the lower jaw, its slenderness and the regular curvature of 



*Scott, W. B. The Osteology of Hyaenodon. Jour. Acad. Nat. 

 Sci., Phila., Vol. 9, 1894, pp. 499-535. 



