Anthropoid 



1 2 4 5 



0 1 2 



i i I 



centimeters 



Lower ends of three humeri, or upper arm bones (shown 

 slightly larger than life size, front view at left, back view at 

 right), provide a basis for comparing three fossil primate 

 species: the notharctic Smilodectes mcgrewi (top), an 

 adapoid that lived about 45 million years ago in North Amer- 

 ica; Pondaungia (middle), one of the amphipithecids discov- 

 ered in 37-million-year-old deposits in Myanmar (formerly 

 known as Burma); and Aegyptopithecus zeuxis (bottom), one 

 of the early north African anthropoids, which dates from 

 about 32 million years ago. Points of comparison, such as the 

 numbered features highlighted in the drawings, suggest that 

 the amphipithecids were closely related to the adapoids. 



with earlier fossil anthropoids. A more enlightening 

 comparison comes from the fossils unearthed at the 

 Fayum site in Egypt, as well as elsewhere in North 

 Africa, where work has progressed in recent years. 



By the 1960s two main groups of Fayum anthro- 

 poids had been discovered. The more primitive of 



the two vaguely resembled modern South American 

 monkeys; the more advanced group looked much 

 like modern Old World monkeys and apes. All of 

 them were thought to date from a period older than 

 25 million years and perhaps as far back as 30 million 

 years. Thus the Fayum anthropoids appeared to be 

 younger, by at least 10 million years, than the am- 

 phipithecids, which at the time were thought to date 

 from about 40 million years ago. Both the Burmese 

 and African finds had deep jaws and large, flat teeth, 

 and individuals in both groups were relatively large 

 compared to the prosimians. It was quite plausible to 

 suggest that the amphipithecids could have been an- 

 cestors of the Fayum anthropoids. 



As work continued in the Fayum, however, along 

 with other work in Morocco and Algeria, several 

 things happened that led to a much more complete 

 picture of North African primate evolution. First, ad- 

 vances in dating technology proved that the primate- 

 bearing rocks in the Fayum spanned an earlier time 

 period than previously thought, between 37 million 

 and 31 million years ago. Second, better specimens 

 of previously known forms were discovered. And 

 third, new anthropoids from older rocks in the Fayum 

 and in Algeria and Morocco were discovered. 



The earliest known anthropoids from Algeria and 

 the earliest parts of the Fayum turned out to be as 

 small as, or even smaller than, their prosimian rela- 

 tives. They also proved to date from between 50 

 million and 37 million years ago, making them as 

 old as or older than the amphipithecids. Given that 

 the age of the Myanmar amphipithecids is now firm- 

 ly fixed at about 37 million years ago, it is difficult 

 to imagine how they could have been the ancestors 

 of older African anthropoids. If that were not evi- 

 dence enough, the teeth of the amphipithecids have 

 more in common with those of the later and larg- 

 er Fayum primates than they do with the teeth of 

 the earlier ones. It has also become clear that all the 

 African skulls, in contrast with the possible skull 

 fragments of the amphipithecids, shared the spe- 

 cialized features characteristic of living anthropoids. 



So how do the curious amphipithecid primates 

 from the Pondaung Hills fit into the primate 

 group as a whole? Are they the lone representatives 

 of an isolated and long-extinct primate line? Or do 

 they share features with some other, non-anthropoid 

 primate group? We favor the second hypothesis. 

 Nearly all the features of amphipithecids are also 

 characteristic of a group of lemurlike prosimians that 

 flourished across all of the northern continents be- 

 tween 55 million and 34 million years ago. 



Those latter prosimians, comprising the adapids 

 and the notharctids, form a group known as adapoids, 



58 



NATUKAl HISTORY March 2006 



