THE ELEPHANTS AND SEA COWS 225 



that the forerunner of these animals was a terrestrial Mammal 

 not very different from the Egyptian Eocene Ungulate Moeri- 

 therium the relationship of which to the ancestor of the Ele- 

 phants has already been pointed out. We infer that this 

 Oligocene predecessor early assumed an aquatic existence and 

 that some members migrated from the Mediterranean to the 

 Atlantic basin finally evolving into the Manatees while others 

 entered the Indian Ocean to give origin to the Dugong. Why 

 tooth reduction occurred finally in the latter and tooth in- 

 crease in the former we do not know. 



The number of genera of Sirenia, so far as we have evidence, 

 was never very large but from such fossil forms as are known it 

 is accepted that the primitive Ungulate ancestor of the order 

 was a terrestrial, five toed, short legged animal with the usual 

 primitive dental formula, brachyodont bunodont molars, hinder 

 premolars molariform, anterior ones simple, small canines 

 and a tendency to the tusk-like elongation of one upper and 

 one lower incisor on each side. 



