214 INTRODUCTION TO EVOLUTION 



Eurasia and Africa, the last survivors being found in African Pleistocene 

 deposits. 



Gomphotherium 



One group of proboscideans specialized in elongation of the lower jaw. 

 Typical of this group is the Miocene form, Gomphotherium (Fig. 10.15). 

 The most extreme lower jaw recorded was six feet and seven inches in 

 length. While some of the jaws were very slender, approaching the 



FIG. 10.15. Skull of Gomphotherium. (From Rotner, Vertebrate Paleontology, University 

 of Chicago Press, 1945, p. 409.) 



mechanical limit, jaws of other species formed a shovel-like arrangement 

 which may have been of use in digging for food. The molar teeth were 

 large, but were low-crowned, with long roots. The largest species of 

 Gomphotherium had a height of about 7 feet and was massively built. 

 Gomphotherium is of interest as the first proboscidean to reach North 

 America, presumably as a migrant from Asia. 



Mastodons 



Another line of proboscideans culminated in the mastodons (Fig. 10.16). 

 These were creatures of elephantine size that roamed North America 

 until postglacial times, as judged by the fact that their bones are found 

 near the surface in bogs and swamps. The mastodon lower jaw was short 

 (Fig. 10.16), usually without tusks, although rudimentary lower tusks are 

 found in some specimens. The upper tusks were large, sometimes attaining 

 a length of 9 feet, and curved upward. The skull contained an extensive 



