112 The Badftand; Formations of the Black Hill© Region 



They are distinguished from all other American ruminants 

 by the combination of functionally tetradactyl front feet with 

 didactyl hind feet. Of the seven genera thus far recognized 

 from the Black Hills region, Protoceras is the most interesting 

 and the best known. It is found only in the Upper Oligocene 

 and because of its importance the strata containing it are known 

 as the Protoceras beds. Of the other genera Leptomeryx has 

 been most carefully described but the materials available have 

 not been so abundant nor so complete as in the case of 

 Protoceras. 



The first Protoceras specimen was obtained by Mr. J. B. 

 Hatcher in 1890. It, like all subsequent material of this kind, 

 was' found near the highest part of the Big Badlands, where the 

 Protoceras beds are well exposed. In January 1891 Prof. 

 Marsh described the animal in the American Journal of Science 

 under the name Protoceras celer in allusion to the early appear 

 aiice of horns in this fleet-footed group of artiodactyls. Before 

 this discovery no horned artiodactyls were known to have lived 

 earlier than Pliocene time. Marsh states it as an important fact 

 that while all existing mammals with horns in pairs are 

 artiodactyls and none of the recent perissodactyls are thus 

 provided, the reverse of this was true among the early forms of 

 these groups. 



The head is especially unique (see Plate 46). It displays in 

 many ways the modernized type of structure and shows sexual 

 differences unparalelled among the ancient artiodactyls. The most 

 obvious characters are the bony protuberances from various 

 j. arts of the head in the male. In the female these are only 

 faintly indicated. In the male a pair of protuberances project 

 upward from the rear part of the head in much the same posi- 

 tion as the horns of the present day pronghorn antelope. Near 

 the anterior end of the face there is a second pair, laterally 

 compressed and more prominent than the first pair. Over the 

 eyes there is a third pair serving as a sort of protective awning 

 for the eyes. In front of these and slightly nearer the median 

 line of the face there is a fourth pair. These are much less 

 prominent than the others mentioned but their presence is 

 clearly indicated. Finally a fifth pair, slightly more prominent 

 than the last, but less prominent and especially less hornlike 

 than the others, is placed at the side of the face nearly above the 

 anterior molar tooth. 



The head is long and narrow, tapering rapidly toward the 



