THE THEORY OF ORGANIC EVOLUTION 183 



Mastodon 



HIDOLE M/OCENE 



North America 



LOMR MIOCENE 

 UPPfROUGOCENE 



Gompholherium 

 wsfidens 

 \Jono chin, 



anousfidens sfaye 

 (/ono cA/'/ 



LOWttOUGOCENE 



PoloeotnasTodonfr UPPER EOCENE ( 



Hoe nf her/urn ft 



fo/oeomasfodoh 



MIDDLE EOCENt \ 



FIG. 24. Evolution of the Elephant. (From Scott, "Land Mammals of West- 

 ern Hemisphere," published by the Macmillan Co. Reprinted by per- 

 mission.) 



