MAMMALIA 



397 



these aquatic mammals has always been alongside the Cetacea 

 (whales), but the resemblances between these two aquatic groups 



FIG. 203. Evolution of head and molar teeth of mastodons and elephants. 

 A, A', Elephas, Pleistocene; B, Stegodon, Pliocene; C, C', Mastodon, Pleistocene; 

 D, D', Trilophodon, Miocene; E, E', Palcp.omastodon, Oligocene; F, F', Mcerithwium, 

 Eocene. (From Lull.) 



