450 LAND MAMMALS IN THE WESTERN HEMISPHERE 



therium and its skull might be described as a preliminary sketch 

 for that of the latter ; the nasal horns were extremely small, or, 

 more probably, entirely absent; the median pair were mere 

 low knobs, hardly an inch in height, and the posterior pair 

 were simply thickenings of the crest which enclosed the top of 

 the cranium on three sides, scarcely rising above it. This 

 crest itself was much less prominent than in fUintatherium 

 and the basin-like top of the skull, in consequence, very much 

 shallower. The upper incisors and the first premolar had 

 already been lost and the upper canine enlarged into a sabre- 

 like tusk, which, however, was relatively smaller than in the 

 succeeding genera. The grinding teeth were quite the same 

 as in the latter. Unfortunately, the skull of \Elachoceras 

 is the only part of the animal which is known, but, so far as 

 that is concerned, it is precisely, what we should expect the 

 forerunner of \Uintatherium to be ; an ajic^stor made to order 

 could hardly be more diagrammatic. It might, of course, be 

 objected that no such relation as that of ancestor and de- 

 scendant could obtain between these two genera, because they 

 were contemporaries, but the case is like that of the ancestral 

 elephants described in the preceding chapter. \M(£ritherium 

 and ^PaloBomastodon are found together in the Egyptian 

 Oligocene, the former surviving for a considerable time after 

 it had given rise to the latter, and in the upper Eocene only 

 \M(Britherium occurs. Many similar instances might be 

 given, just as grandfathers often live long with their grand- 

 children. 



In the Wind River stage, or upper division of the lower 

 Eocene, lived the still incompletely known ^Bathyopsis, of 

 which, however, sufl&cient material has been obtained to show 

 that it was much less specialized than any of the Bridger genera. 

 This genus comprised animals much smaller than its successor, 

 ^Elachoceras of the middle Eocene, being smaller than a tapir ; 

 it stood in much the same relation to ^Elachoceras as the latter 

 did to \Umtatherium. In the American Museum of Natural 



