When Primates Went Ape

From a chaotic prehistoric world teaming with 30 different kinds of apes, a single lineage survived to give rise to modern apes and humans. Now, thanks to new fossil finds, two African primates are claiming prime ancestral spots on the ape family tree. These discoveries, reported at a recent scientific meeting and in tomorrow's issue of Science,* may push the emergence of a modern apelike body plan back by 5 million years.

New fossils of one contender, the 14-million-year-old Kenyapithecus, were presented earlier this month at the annual meeting of the American Association of Physical Anthropologists. Working with 135 excavators at their site on Maboko Island in Kenya's Lake Victoria last summer, paleoanthropologists Monte McCrossin and Brenda Benefit of Southern Illinois University found new fossils of this ape to add to the existing collection of Kenyapithecus specimens. Modern features of the new fossils, including the straightness of an upper arm bone and an unusually shaped ankle bone, tie this ape to living ones and make Kenyapithecus "the best, most likely ancestor of humans, chimps, and gorillas," claims McCrossin.

But Northern Illinois University anthropologist Daniel Gebo and colleagues propose in Science that a larger, tree-dwelling ape called Morotopithecus is an even older ancestor. Morotopithecus was also previously known from fragmentary fossils at a site called Moroto in Uganda, but now Gebo and Laura MacLatchy of the State University of New York, Stony Brook, and colleagues have found an additional partial shoulder bone and parts of two leg bones. Not only did precision dating show these fossils to be at least 20.6 million years old--5 million years older than had been thought--but they were unexpectedly modern. The shoulder socket, for example, was round, suggesting that Morotopithecus could hang by its arms in trees like living chimpanzees and orangutans. "Given these traits, we think it was a sister species to living apes," says MacLatchy.

The findings will force researchers to "rethink all of the relationships of apes in the Miocene," a period from 5 million to 23 million years ago, says University of Missouri paleoanthropologist Carol Ward. But not everyone is convinced that either Morotopithecus or Kenyapithecus is such close kin to living apes and humans, noting that the recent conclusions are based on fragmentary fossils. "I think we can expect continuing clouds of discomfort as to how to handle all this new material," says paleoanthropologist John Kappelman of the University of Texas, Austin. "But it's the beginning of a great research enterprise."

* For more details, Science Online subscribers can link to the full text of the Report.