120 MAMMALIAN DENTITION 



also to be noted. In Alouatta the lower molars are subequal in 

 size and elongated from the presence of a large talonid. The 

 protoconid and hypoconid are well-developed cnsps which by 

 continuation into the anterior and posterior bounding ridges 

 respectively of the tooth become crescentic, the concavity of 

 the crescent being directed inward. As in Ateleus the para- 

 conid is lost and the metaconid has extended forward. An- 

 other feature associated in Alouatta with the purely herbiv- 

 orous diet is the upward extension of the mandibular ramus 

 which brings the condyle to a level far above that of the molar 

 teeth. 



If reference now be made to the marsupial dentitions of the 

 Phalanger (page 82) and the Koala (page 83), it will be seen 

 that in their cheek teeth patterns these resemble in general 

 the dentitions of Ateleus and Alouatta respectively, since simi- 

 lar food habits tend to call forth corresponding modifications 

 in dentition, especially in the molar series, of animals belong- 

 ing to widely different orders. 



THE OLD-WORLD MONKEYS AND APES 



All existing Old-World Monkeys are specialized. Hence to 

 render the successive adaptation more intelligible the earliest 

 and most primitive species yet discovered, namely Parapithe- 

 cus, is introduced (Fig. 41). This animal lived in Egypt dur- 

 ing the Oligocene and is known from the mandible alone. The 

 jaw presents a superficial resemblance to that of Tarsius. In- 

 deed the same dental formula has been given to both though 

 it now appears that the formula for Parapithecus should read: 



The resemblance alluded to is not confirmed on closer investi- 

 gation and this is scarcely remarkable for Tarsius is a modern 

 type specialized in many respects whereas Parapithecus is an 

 early and more generalized form. 



M^m 



