462 EVOLUTIONARY MORPHOLOGY 



The Catarrhinae must have emerged in the Eocene period 

 from Tarsioid ancestors related to those which gave rise to the 

 Platyrrhinae. In the Oligocene, Parapithecus is found, and 

 from forms related to it the ordinary monkeys or Cercopithe- 

 cidae must have been derived. These forms are again ruled 

 out from the main line of Primate evolution by specialisations 

 such as the development of two transverse ridges on the 

 molars. At the same time, the Cercopithecidae, which include 

 the baboons and mandrills, show a great development of the 

 brain, which must have undergone an evolution parallel to 

 that which went on in the stock leading to the apes and man. 



The main stem of the Primates leading to the anthropoid 

 apes and man was represented in the Oligocene by the little 

 Propliopithecus. The fact that it was small is important, for 

 so many divergent branches became specialised in the direction 

 of large size, and in the search for the ancestors of the apes 

 and man, choice is limited to forms considerably smaller than 

 those to which they might have given rise. The anthropoid 

 apes have lost the tail, they show a tendency to walk erect, 

 the mechanism of pronation and supination of the hand is 

 perfected, and the brain is greatly enlarged and developed. 



A descendant of Propliopithecus was the Pliocene form 

 Pliopithecus, which itself was an ancestor of the gibbon 

 (Hylobates), the smallest of the apes. Other lines of descent 

 from forms like Propliopithecus led to the Orang, and to the 

 chimpanzee and Gorilla, while the main stem culminated in 

 the Hominidae and man. The apes while having highly 

 developed brains and retaining the power to oppose the first 

 toe to the others, have not got brains large enough to enable 

 them to do otherwise than remain brutes, relying on their 

 strength and their long canines instead of on memory, skill, and 

 the neopallium. There are some characters possessed by adult 

 modern man which are present in the young but lost in the 

 adult apes. An example of these is the absence of large 

 brow-ridges in young apes and man. 



The fossil record of the Hominidae is not by any means as 

 complete as would be desired, but there is already sufficient 

 evidence to enable an outline to be given of the more important 



