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 ma.stodons and elephants. 

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

 D, D', Trilophodori , Miocene; E, E', Paliromastodon, Oligocene; F, F', Mcerithervmn, 

 Eocene. (From Lull.) 



