CHANGES OF PROPORTION 



269 



demonstrated by the universal law that the limb proportions 

 of mammals are closely adjusted to provide for escape from 

 enemies at each stage of development. 



Africa as a Great Theatre of Radiation 



The part which Africa has played in the early stages of 

 mammalian evolution is a matter of comparatively recent dis- 

 covery, and we are not yet 



. i 

 positive whether the great life 



centre of North Africa was not 

 closely related to that of south- 

 ern Asia in Eocene and early 

 Oligocene time, as the most re- 

 cent discoveries appear to indi- 

 cate. At all stages of geologic 

 history Africa was, as it is to- 

 day, a great theatre of evolu- 

 tion of terrestrial life. Accord- 

 ing to present knowledge. North 

 Africa developed a highly varied 

 fauna, including three chief ele- 

 ments: first, types which are 

 closely ancestral to the higher 

 monkeys and apes, and which 

 may thus be related to man him- 

 self; second, a series of forms 

 which attained gigantic size and 

 never migrated from the con- 

 tinent of Africa, but became 

 extinct; and, thirdly, a series of forms, such as the zeuglodons, 

 ancestral whales, sirenians, manatees, and dugongs, which 

 emerged from this African home and enjoyed a very wide dis- 



FiG. 131. Epitome of Proportion Evo- 

 lution IN THE PrOBOSCIDEA. 



These animals originated in the Palcco- 

 niastodon (lower), frequenting the an- 

 cient borders of the Nile in Egypt dur- 

 ing Oligocene time, which developed 

 during a period of 1,500,000 years into 

 the existing types of the Indian and 

 African elephants and into the ancient 

 type of the Elephas (upper). 



Restoration in the American Museum of 

 Natural History under the direction of 

 the author, painted by Charles R. 

 Knight. 



