116 MAMMALIAN DENTITION 



of the hinder ends of the upper dental arch and the extension 

 of the palate as far back as the last molar are of course ac- 

 counted for by the narrowing of the entire palate and the 

 small size of the degenerate cheek teeth. The milk dentition 

 of this animal is much more lemurine than the permanent set. 

 The Aye-aye in fact is a remarkable instance of convergence 

 in evolution. In Madagascar as in Australia there are prac- 

 tically no Rodents. In the one island the Aye-aye and in the 

 other the Wombat takes their place and presents similar modi- 

 fications in its dentition. 



In general the Lemurs are a most interesting suborder for 

 they show excellently many variations possible in dentition 

 following changes in life habits and in diet but all originating 

 from a single central type. The modern representatives of the 

 suborder though widely distributed from Africa through India 

 to the Malay Archipelago are very definitely divided into two 

 groups, the Malagasy and non-Malagasy. These two groups 

 have evolved along parallel lines but have been separated 

 from each other ever since Madagascar was cut off from Africa 

 at the base of the Tertiary. Existing forms are very specialized 

 and largely decadent as already stated. 



In the evolution of the Lemurs there has been a gradual 

 loss of premolars until only the third and fourth of the orig- 

 inal series remain for whereas the extinct Adapidae possessed 

 four premolars, the majority of living Lemurs have but three 

 and the Indrisinae only two. There is no doubt that a similar 

 process of reduction has occurred in the Monkeys and Apes. 



It is instructive to note that among the Indrisinae there has 

 been a type iioav extinct but represented during the Pleistocene 

 by the species Paleopropithecus in which the dentition was 

 adapted for a purely herbivorous diet and which considerably 

 resembled in consequence that of modern Baboons. This is 

 another instance of parallel evolution. 



In the Primates reduction in the number of incisors took 

 place very early; reduction in the premolar series occurred 

 later and probably more slowly. Among the Anthropoidea 



