EVOLUTION OF THE ELEPHANT LULL. 



659 



Fig. 17. — Skull of the American mastodon. 



the only proboscidians to cross into the southern hemisphere of the 

 New "World. Some of these animals lived in the high Andes at an 

 elevation of 12,350 feet above the level of the sea at a time when the 

 region had a greater rainfall than now and therefore a richer vege- 

 tation. 



Mammut. 



This genus reaches its culmination in the American mastodon, a 

 creature of great bulk, though about the height of the Indian ele- 

 phant. It was, however, 

 much more robust, a fea- 

 ture especially noticeable 

 in the immense breadth of 

 the pelvis and the massive- 

 ness of the limb bones. 

 The feet were more spread- 

 ing than in the true ele- 

 phants, which, together 



with the character of the teeth and the conditions under which the re- 

 mains are found, points to different habits of life from those of the 

 mammoth, the mastodons being more distinctively forest-dwelling 

 types. The skull differs from that of the true elephants in its lower, 

 more primitive contour, for while there is a large development of air 

 cells in the cranial walls the brain cavity is relatively larger- The 

 tusks are well-developed, powerful weapons, not so sharply curved 

 as in the elephants, though in this respect individuals vary. The 



tusks are very heavy at the base 

 and taper rapidh^, curving inward 

 at the tips. In the lower jaw the 

 tusks are vestigial, being apparently 

 present only in the male. Usually 

 they are soon shed, and the sockets 

 may entirely disappear, as in the 

 Otis vi lie mastodon at Yale, whereas 

 the Warren mastodon now in the 

 American Museum, a fully adult animal, retained the left lower tusk, 

 which is about 11 inches in length. The socket of the right tusk 

 is also still distinct. 



The grinding teeth Avere of large size, two in each half of either 

 jaw, as in the Tetrahelodon, but the crests are simpler Avith but few 

 accessory cusps. The crown of the tooth is covered with thick enamel, 

 which in turn is overlain by a thin layer of cement before it cuts the 

 gum. This is soon removed by wear. These teeth are admirably 

 adapted for crushing succulent herbage such as leaves and tender 

 twigs and shoots, but not for grinding the siliceous grasses which 

 form a necessar}- part of the food of the true elephants. '' Broken 



Fig. 18. — Tooth of mastodon (X J). 



