THE HISTORY OF THE PRIMATES 



tions of the teeth which characterize modern lemurs. Of somewhat later 

 date ( Oligocene ) , is the tree shrew Anagale, of especial interest because 

 it is in many respects intermediate between tree shrews and lemurs. While 

 its general features are those of the tree shrews, certain features of the 

 skull and of the molar teeth are lemuroid. Also, the digits were capped 

 by nails rather than claws. While this animal could not be ancestral to 

 Adapts (because it occurred later), it indicates the probability that simi- 

 lar tree shrews of an earlier time may have been ancestral to lemurs. 



Tarsiers were present in great abundance in the Eocene, for no less 

 than twenty-five genera are known from Europe and America. Some of 

 these were quite similar to the modern tarsier (Figure 64). Others were 

 decidedly more primitive in skull pattern, brain, and limbs. Some retained 

 the primitive insectivore dentition of forty-four teeth, while others had 

 the dentition reduced to thirty-two, the number characteristic of the 

 higher Primates. Other changes in the teeth of these Eocene tarsiers also 

 tended in the direction of the higher Primates. Thus they were the first 

 Primates to develop bicuspid premolars. The molars of the tree shrews 

 and insectivores have three cusps, but some of the Eocene tarsiers, in 

 common with all of the higher Primates, have molars with four cusps. 

 Thus many of these primitive tarsiers had decidedly monkey-like features. 

 It is a much debated question whether the tarsiers were derived directly 

 from the tree shrews or whether they were derived from very primitive 

 lemurs. 



APES IN THE FOSSIL RECORD 



Parapithecus and Propliopithecus. Anthropoid apes first appear in 

 the fossil record in the Oligocene epoch, but these remains are very scant 

 indeed, being known only from two lower jaws found in Egypt, The first 

 of these was described under the name Parapithecus. A single jaw gives 

 a very scant basis for judgment, but some conclusions can be drawn. The 

 first of these is the fact that anthropoids did exist as long ago as the Oligo- 

 cene (although the anthropoid and even primate status of Parapithecus 

 has been seriously contested ) . Parapithecus was a small animal, about the 

 size of the little squirrel monkey, and it was very primitive. It had the 

 dental formula characteristic of Old World monkeys and anthropoids, that 

 is, there were in each half jaw two incisors, one canine, two premolars, 

 and three molars. The canines were no larger than the adjacent incisors 

 and premolars, unlike the modern apes in which the canines form power- 

 ful tusks. Also, there was no simian shelf, the shelf of bone connecting the 

 two sides of the lower jaw of modern apes. The premolars were tarsioid in 

 character, a fact wliich has been interpreted to mean that the apes were 

 derived from tarsiers independent of the monkeys. In other words, the 

 three superfamilies of the suborder Anthropoidea may have been separate 

 since their origin in the late Eocene or early Oligocene. The molars, how- 

 ever, are anthropoid in character. The second genus, Propliopithecus, was 

 larger, and more specialized. It is regarded as being already on a collateral 

 line of descent leading toward the gibbons and siamangs of today. 



183 



