FOSSIL ANIMALS 



33: 



the .skull was distinctly higher {E') with a greater development of 

 cancellate bone, and the neck was somewhat shortened. The upper 

 incisors of the second pair were more elongated as tusks; the lower 

 second incisors were present, but not enlarged; while all other incisors 

 and the canines had disappeared. The molar teeth {E) resembled those 

 of Moeritherium but were larger. The lower jaw was considerably 

 elongated, and the number of permanent teeth was reduced to 26. The 

 nasal openings had receded until they were just in front of the eyes, 

 which is believed to indicate the existence of a short proboscis extending 

 at least to the tips of the tusks. 



Trilophodon, a great migrant and consequently widespread over 

 several continents in Miocene time, Avas a huge animal, nearly as large 

 as modern Indian elephants. The tusks were considerably longer (-D')- 

 The molar teeth were large and greatly 

 reduced in number, so that only two were 

 present at any one time on each side of 

 each jaw. The surface of these teeth 

 bore a somewhat larger number of trans- 

 verse crests {D) than were present in the 

 earlier forms. The lower jaw was enor- 

 mously elongated, so that it projected as 

 far forward as the tusks. There was a 

 considerable development of cancellate 

 bone in the skull, to which the supporting 

 muscles of the neck were attached. The 

 long lower jaw, which was not continued 

 in later forms, has led paleontologists to 

 conclude that Trilophodon was not in the 

 direct line of descent, but that it was an 

 offshoot. Dinotherium (Fig. 286, upper left), a contemporary of 

 Trilophodon but with a strongly recurved lower jaw, is likewise 

 regarded as a lateral branch. 



The mastodons were somewhat larger than Trilophodon, being about 

 the size of the Indian elephant. The tusks {€') were much elongated 

 (9 feet or more), but the lower jaw was greatly shortened and the lower 

 incisor teeth were reduced or wanting. The molar teeth (Figs. 283C, 

 284) were scarcely more complex than earlier forms and numbered 18 to 

 20 in the permanent set. They were still crushing teeth, and the food 

 must have been tender twigs and succulent plants; indeed, remains of 

 such objects have been found in the region of the stomach of some of 

 the fossil mastodons. 



Apparently arising from the primitive mastodons was Stegodon, 

 knoAvn only from Asiatic Pliocene. Its molar teeth (Fig. 283 i?) had 



Fig. 284. — Mastodon tooth, 

 showing the enormous cusps on the 

 upper surface. {From a California 

 specimen in the Museum of Geology, 

 University of Michigan.) 



