204 R. S. Lull— Evolution of the Elephant. 



gave rise to a remarkable group of four-tusked mastodons 

 which ranged from Nebraska to Florida. From some of the 

 later species arose the Dibelodon race with upper, enamel 

 banded tusks, but lacking those of the lower jaw. This genus is 

 reported from the Pliocene (Blanco) of Texas and Mexico and 

 ranges as far south as Buenos Aires in the southern hemisphere. 

 Two South American species are known to us, one, D. andium, 

 following the chain of the Andes as far south as Chili. This 

 type is often found at great altitudes, a specimen from the 

 Quito valley in Ecuador, now in the Yale collection, having 

 been found 10,000 feet above the level of the sea. 



Dibelodon humboldii was a dweller on the plains, being 

 found ih the pampas formation near Buenos Aires, while 

 Darwin records it along the banks of the Parana river in 

 Argentine, and Wallace reports the same species among other 

 remains in a limestone cavern near the headwaters of the San 

 Francisco river in southern Brazil. D. humholdii, like 

 D. andiu?n, has its origin in the Texas Pliocene, the line 

 of migrations nearly paralleling, the one along the tropical 

 plains, the other along the Andine plateau as far south as 

 northern Chili. With the exception of a lone specimen of 

 Elephas reported from French Guiana and the mastodon of 

 Honduras, Dibelodon is the only proboscidian of the Neotropical 

 realm. The migration of these great forms occurred in the late 

 Pliocene, and for some reason, evidently climatic and vegetative, 

 the route has been closed ever since. Otherwise it is reason- 

 able to suppose that the elephants and mastodons of the Pleis- 

 tocene would have spread into South America as well. 



In Europe Teirabelodon angustidens had successors in T. 

 longirostris and arvemensis, the latter ranging over western 

 Europe into England. It did not, however, cross the Pyrenees 

 into Spain. T. longirostris and a late mutation of T. angusti- 

 dens, palceindicus, made the long journey to the Orient, trans- 

 ferring the evolution from Europe to India. The path of this 

 migration is as yet unknown, as little or no paleontological ex- 

 ploration has been made in the region lying between Armenia 

 on the west across Persia, Afghanistan, and Beluchistan to the 

 Indus river. This oriental migration must have occurred 

 during the Upper Miocene and was followed by a relatively 

 rapid evolution involving a number of species of mastodons 

 and elephants. Tetrabelodon longirostris seems to have given 

 rise to Mammut* cautleyi with a shortened lower jaw, thence 

 through 31. latidens to Stegodon clifti, the transitional form 

 between the mastodons and the elephants. 3. clifti was followed 



* These Indian forms agree probably with the American mastodon in 

 having but one pair of enamelless tusks. They may represent the Mammut 

 stage but in an entirely different phyluni, hence should not bear the same 

 generic name. 



