476 



THE CHANGING GENERATIONS 



like the lemurs in appearance. They are squirrel-like forms with short fur 

 and bushy tails; the first toes have flat nails and are not opposable, while 

 the other toes have claws. The remaining platyrrhines (Cebidae) are 

 more familiar types of monkeys, such as the capuchins ("hand-organ 



monkeys"), howlers, squirrel mon- 

 keys, woolly monkeys, etc., which 

 have flat nails on all digits, and 

 most of which have prehensile tails. 

 The cata r rhines. This Old World 

 group includes the African and 

 Asian monkeys, the manlike apes, 

 and man. In all of these the 

 nostrils are placed rather close 

 together and open forward and 

 downward. The tooth formula is 

 the same as in man — two incisors, 

 one canine, two premolars, and three 

 molars in each tooth row. All the 

 digits have flattened nails, and the 

 tail (which may be long, short, or 

 rudimentary) is never prehensile. 

 The catarrhines show a general tend- 

 ency toward increased size, which 

 among living forms culminates in 

 the chimpanzee, man, and the 

 gorilla. Most members of the group 

 are arboreal, but a few, such as the 

 baboons and man, have become 

 ground dwellers. From the original 

 quadrupedal climbing and jumping 

 mode of locomotion some lines have 

 progressed to brachiation, with 

 elongation of the arms and assump- 

 tion of partially erect posture. In 

 man alone the posture has become 

 fully erect. 



The Old World monkeys. The 

 earliest known member of this group 

 is a tiny monkey called Parapithecus, from the lower Oligocene of Egypt. 

 Judging from the characters of its jaw and teeth (Fig. 29.14), it may well 

 have been the ancestor of all the later catarrhines. Today the Old World 

 monkeys comprise many genera and species, all placed in the family 

 Cercopithecidae. They are easily distinguished from the American 



Fig. 29.6. A langur monkey, Semnopithe- 

 cus, from the Nilgiri Hills of India. These 

 monkeys, of the family Cercopithecidae, 

 lack cheek pouches and have a complicated 

 stomach for food storage. (Courtesy Amer- 

 ican Museum of Natural History.) 



