EVOLUTION OF MAN 221 



Primates are also characterized by many other features, such as posses- 

 sion of a single pair of mammary glands, usually pectoral (on the chest) 

 in position, complete separation of the eye orbit from the temporal fossa 

 by a partition of bone, and so on. The sample given is sufficient to 

 emphasize the many features shared by man with his fellow primates. 



Beginnings of Primate Evolution 



The Order Primates is conveniently divided into two suborders: 

 Suborder Prosimii (tree shrews, lemurs, tarsiers) and Suborder Anthro- 

 poidea (monkeys, apes, men) (Simpson, 1945). Among the prosimians the 

 tree shrews ( Fig. 11.1) are the most primitive, resembling both insectivores 

 and primates in structure. Indeed they were formerly classed as members 

 of Order Insectivora. It seems highly probable that tree shrews living in 

 early Cenozoic times were at once the descendants of true insectivores 

 and the ancestors of higher primates. 



The immediate descendants of these tree shrews were lemurs and 

 tarsiers, both represented by numerous forms in early periods of the 

 Cenozoic era. Lemurs are small animals resembling monkeys in many 

 ways, as, for example, in having hands tipped with flattened nails instead 

 of claws. Even so, some lemurs have a specialized claw on one digit of 

 each hand. The faces of lemurs project into unmonkeylike muzzles, 

 however, suggesting the faces of little dogs (Fig. 11.1). Tarsiers are 

 represented today by only one form, the spectacled tarsier, found in 

 some islands of the East Indies. This animal is remarkable for its enormous 

 eyes and concomitant development of the visual regions of the brain 

 (Fig. 11.1). 



Did tarsiers evolve from lemurs or did they arise directly from tree 

 shrews? Authorities differ on this question. But significantly, in the case 

 of some of these early Eocene prosimians "it is a matter of great 

 difficulty to decide whether they should be classified as lemurs or tarsiers" 

 (Le Gros Clark, 1949-1957). This suggests their close relationship. On the 

 other hand, some of the Eocene tarsiers resembled monkeys in dentition 

 and skull characteristics and hence may well have been ancestral to 

 higher members of the order. At any rate it is clear that early Cenozoic 

 prosimians were the ancestors of higher primates. 



Monkeys, Apes, and Men 



Suborder Anthropoidea is divided into two groups: (1) New World 

 monkeys, and (2) Old World monkeys, apes, and men. Man resembles 



