MASTODON. 33 



MASTODON. 



In Tetrabelodon longirostris the main characteristics of the 

 modern elephants are already established, and the later changes 

 of importance include, (1) the still further reduction of the 

 inandibular symphysis and the loss of the lower incisors, and 

 (2) the great increase in the size and complication of the 

 cheek-teeth. It will be convenient to consider these changes 

 separately. 



In the shortening of the chin the next stage is found in 

 Pliocene forms like Mastodon atticus ( Pier-case 37) from the 

 Lower Pliocene of Pikermi. In this the symphysis, though 

 much shortened, is still more or less spout-like, and in very 

 young individuals the incisors may be present, though they are 

 soon shed ; .the absence of these teeth in the adult is the chief 

 character distinguishing the genus Mastodon (fig. 19) from 

 Tetrabelodon. One of the best-known species belonging to this 

 stage of development is Mastodon arvernensis (Pier-cases 3740), 

 which is found in Europe in Pliocene deposits; in it the lower 

 incisors seem to be entirely wanting and the anterior molars 

 have four transverse ridges. A nearly allied species, M . sivalensis 

 (fig. 21), from the Pliocene of India, is notable as showing a 

 tendency to acquire five ridges to its molars. 



The region in which the passage from the Mastodons to the 

 true elephants occurred seems to have been Southern Asia, 

 where, in a succession of Pliocene and Pleistocene deposits, 

 there is a complete series of forms passing from the Mastodon 

 up to the recent Indian Elephant (Pier-cases 34-37). 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 Proboscidea make their first appearance in North 

 America in the Miocene, and are there represented by a great 

 variety of forms. Some (see pages 2930) have the lower tusks 

 much enlarged and borne in a down-turned symphysis ; these 

 are regarded by Professor Osborn as belonging to a distinct 

 genus Uhynchotherium ; one of them is shown in figure 17. 

 Others are straigl it-jawed Tetiabelodonts, some with compara- 

 tively short symphyses (e. g., T. productus\ some with the 



