No. 646] THE FOSSIL PROBOSCIDEANS 453 



now found to belong respectively to three distinct lines 

 of the Proboscidea, namely, the moeritheres, the true 

 mastodonts, the long-jawed bunomastodonts, as indicated 

 in black on the accompanying diagram. They point, 

 however, to a long antecedent origin and radiation. This 

 is part of the evidence for an ancient adaptive radia- 

 tion process by which it now appears that the probos- 

 cideans, like other hoofed mammals, were broken up into 

 several great primary stocks way back in Eocene times, 

 namely : 



An amphibious stock, adapted to rivers and swamps, of 

 limited migration {= Mceritherium, Dinotherium) . 

 A mastodont stock, adapted to forests and savannas, of 



wide migration mastodonts, trilophodonts). 

 A stegodon-elephant stock, adapted to southern forests, 

 to grassy plains, to savannas and steppes, of wide 

 migration { = Stegodon, Loxodon, Eleplias). 

 These primary stocks gave off from two to six 

 branches each, so that the Proboscidea as a whole are 

 not two branched {i.e., mastodonts and elephants), as 

 formerly supposed, but many branched or polyphyletic. 

 The forest and savanna browsers and the grazers of the 

 plains and steppes were the long distance travelers and 

 from an African or Asiatic center in Eocene times they 

 reached in the Middle and Upper Miocene all the conti- 

 nents of the world except Australia, while the amphibi- 

 ous forms remained in Africa and southern Eurasia. 

 Certain of these branches, like the true mastodons, are 

 of very great geologic antiquity. Intelligent, independ- 

 ent, well defended, resourceful, adaptive, w^e find eleven 

 very distinct branches of proboscideans persisting into 

 Upper Pliocene times, five of the least hardy of which 

 became extinct during the colder conditions of the Lower 

 Pleistocene. The known lines of evolution are shaded 

 on the accompanying diagram; the unknown are left in 

 white. The theoretic adaptive radiation may be ex- 

 pressed in a formal classification as follows : 



