174 



EVOLUTION AND GENETICS 



The chief features of the direct line of evolution of the elephants 

 are graphically illustrated in Figure 100. Here the steps leading 

 gradually from teeth with distinct cusps to those with fine trans- 



Fig. 100. — Evolution of the head and molar teeth of proboscideans. A, A'; 

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

 D, D', Trilophodon, Miocene; E, E', Palaeoviastodon, Oligocene; F, F,' 

 Moeritherium, Eocene. (From Lull.) 



