THE ANIMAL ANCESTRY OF MAN 75 



known, was closely related to the existing opossums, which 

 are arboreal. 



THE PRIMATES ASCEND INTO THE TREES 



The high grade of vitahty, the relatively advanced 

 methods of reproduction and a progressive improvement 

 in brains and intelligence, all led to the final triumph of the 

 placental mammals over their competitors the marsupial 

 mammals, which were for the most part crowded into far- 

 away corners of the world auch as Patagonia and Australia. 

 Possibly this higher vitahty of the primitive insectivorous 

 placentals, joined to a high degree of variabihty and plas- 

 ticity in hereditary characters, early enabled them to 

 branch out and adapt themselves for many methods of 

 locomotion and of feeding, according to the w^ell-estabhshed 

 principle of adaptive radiation. Unfortunately the fossil 

 history of the placentals during the later aeons of the Age 

 of Reptiles is extremely meager but early in the Eocene 

 epoch, or first division of the Tertiary period or Age of 

 Mammals, the placental stock had already branched out 

 into insectivores, carnivores, various herbivorous hoofed 

 mammals, rodents and so forth. The direct ancestors of the 

 Primates during this period also are still undiscovered but 

 the fossils from early Eocene times show that even at this 

 immensely remote time (estimated by geologists as perhaps 

 fifty or sixty milhon years ago)(BarreII) the order of Pri- 

 mates had already begun to separate into several of its 

 grand divisions as we know them today: first, there were 

 forerunners of the modern tree-shrews, classed by many 

 authors under the more ancient and primitive order Insec- 

 tivora, but foreshadowing the Primates in many features; 

 secondly, there were primitive lemuroids, structurally 

 at least related to the ancestors of the varied modern 

 lemurs of Madagascar; thirdly, there were the tarsioids, 

 small forms with much enlarged orbits, related to the 

 existing spectral tarsier of the East Indies. 



The higher primates (including the platyrrhine, or New 

 World monkeys, and the catarrhine, or Old World series 

 of tailed monkeys, anthropoid apes and man) do not begin 



