CHORDATA — VERTEBRATA — MAMMALS 



387 



skull due to the development of air cavities and the acquire- 

 ment of the muscular trunk. 



According to present evidence the evolution of the elephant 

 (Fig. 169) began in northern Africa with the mid-Eocene swamp- 

 dweller, Mcerithe- 

 rium ; this seems to 

 have had a prehen- 

 sile upper lip, since 

 the nasal bones were 

 beginning to recede. 

 This recession of the 

 nasal bones became 

 more and more 

 marked, indicating 

 thus a longer and 

 larger trunk, in the 

 line ascending into 

 the modern elephant 

 (Elephas), i.e. Paleo- 

 mastodon, Gompho- 

 therium, Mammut, 

 Stegodon, Elephas. 

 The first of these, 



like its ancestor, Moeritherium, was confined to northern Africa, 

 the rest had migrated more or less fully over the entire Northern 

 Hemisphere. 



In North America the most conspicuous and abundant species 

 during the Pleistocene (Fig. 170) were {a) the American mastodon 

 {Mammut americanum) ranging from Alaska and California to 

 Prince Edward Island, Florida and Central America (Fig. 164, 

 4). The teeth were comparatively small so that two or three 

 could be in use simultaneously upon each side in each jaw. 

 {h) The mammoth {Elephas pr imi genius) , with height usually 

 less than 9 feet, and abundant throughout the Northern Hemi- 

 sphere. It is of this species that complete carcasses have been 



Fig. 168. — Molar tooth of an Indian elephant. A, 

 crown view much reduced in size. B, longitudinal 

 section. Black, portion enamel; dotted, cement; 

 cross-lined, dentine or ivory. Shows the deep in- 

 folding of the enamel and its projection as grinding 

 ridges. (After Lull.) 



