32 ELEPHANTS. 



Pier- where, in a succession of Pliocene and Pleistocene deposits, 

 39^49 there is a complete series of forms passing from the Mastodon 

 up to the recent Indian Elephant. How far these changes 

 may have gone on in the rest of the Northern Hemisphere is 

 not known, but the history of the Mastodons in America is 

 rather different from that of the Old World forms. The first 

 members of the group to appear in North America are found in 

 the Loup Fork (Upper Miocene) beds of Montana, Nebraska, 

 and Kansas, and include Tetrabelodonts and Mastodons, 

 with such species as T. campestris, T. euhyphodon, T. pro- 

 ductus, &c. Some of these species have simpler teeth than 

 T. longirostris, and in this respect approach T. angustidens. 

 The presence of these animals must be attributed to immigra- 

 tions probably from Asia, since no Proboscidean remains 

 occur in the earlier Tertiary beds of North America. The 

 great increase in the size of the lower teeth of T. (?) precursor, 

 just described, seems to show that some of these American 

 species at least had turned away from the main line of advance 

 and become changed in particular directions, so that it is uncer- 

 tain whether the later types, in which the lower tusks were 



Fig. 19. 



Vertical longitudinal section of a molar tooth of a Mastodon, showing the 

 low crown, the open valleys between the cross-ridges and the thick 

 enamel (b). c., dentine. | nat. size. 



reduced and finally lost, are descendants of these or represent 

 further invasions from outside. These later forms spread into 

 South America, where several peculiar species are found which 

 Stand B. persisted with little change till the Pleistocene. Probably the 

 reason why these Mastodons, as well as M. americanus of North 



