Epoch 



Holocene 

 Pleistocene 

 Pliocene 



Miocene 



Millions 

 of Years 

 Ago 



Oligocene 



Eocene 



Paleocene 



Prosimians 



Tarsiers 



Anthropoids 



"i r 



0.01 



1.8 



5.3 



i 



4fs & 



lemurs 



23 



34 



galagos, 

 lorises, 

 and pottos 



55 



66 



adapoids 

 (adapids and 

 notharctids) 



omomyids 



amphipithecids 



New World 

 monkeys 



orangutans humans 

 chimpanzees 

 and gorillas 



eosimiids 



-- ? 



Old World 

 monkeys 



early North 



African 

 anthropoids 



Evidence 



mmm Living forms and 

 related fossils 



— Fossils only 

 ~~ Conjectural 



Primate family tree, based on living species and fossils, leaves much room for conjecture. The 

 amphipithecids, whose fossils have been discovered in Southeast Asia, no longer appear to be 

 closely related to the earliest anthropoids. The origin of the anthropoids remains obscure. 



past three years the two of us have examined near- 

 ly all these amphipithecid specimens. 



Of the forty specimens, two are parts of skeletal 

 bones and another two may be skull fragments; the 

 rest are teeth and jaws. The two skeletal specimens 

 are parts of the arm and the foot; in size, shape, and 

 muscle attachments, both show a close resemblance 

 to the bones of prosimians. 



Some paleontologists have questioned whether the 

 two skull fragments are those of primates — or even 

 skull bones at all. But if they are, they indicate an an- 

 imal that lacked an enclosed eye socket (a bony cup 

 that protects the eye) and had a pair of unfused frontal, 

 or forehead, bones — one on the right and one on the 

 left side of the face, meeting in the so-called metopic 

 suture line. In those respects it contrasts with living 

 anthropoids, which have an enclosed eye socket and 

 a single frontal bone [see illustration on opposite page]. 

 Those two anthropoid features are part of a suite of 

 evolutionary changes in the skull that reflect a reor- 



ganization and enlargement of the brain and an in- 

 creased reliance on stereoscopic vision. 



What about the amphipithecids' teeth? The mo- 

 lars are flat and bulbous, with thick enamel, not un- 

 like the teeth of those living anthropoids whose diet 

 is made up primarily of fruits and seeds. The teeth 

 tend to be crowded together toward the front of the 

 jaws. The canine teeth are robust but not particular- 

 ly tall; in living anthropoids they often differ in size 

 according to sex: the male canines are much larger 

 than the female. At the front of the jaws, the incisors 

 look like small, flat shovels, similar to our own in- 

 cisors. The lower jaws are relatively deep and heavy. 

 On the basis of similar features in living primates, one 

 can inter that the four amphipithecids weighed be- 

 tween three and eighteen pounds and w ere relative- 

 ly slow-moving animals that lived in trees. 



Although the amphipithecids shared only some fea- 

 tures in common with living anthropoids, a more im- 

 portant point is how close they seem when compared 



March 2006 NATURAL HISTORY 



5 7 



