Rare great ape fossil challenges theory of primate evolution

From physorg.com: Archaeologists have discovered the ancient jawbone of what appears to be a new species of ape that was very close to the last common ancestor of gorillas, chimpanzees and humans, a study released Monday said. The 10-million year-old fossil, complete with 11 teeth, was recovered from volcanic mud deposits in Kenya’s Nakali region on the eastern edge of the Rift Valley in 2005 by a team of Japanese and Kenyan researchers. The researchers say the fossil fills what was until recently something of a void in the fossil record, and challenges one of the working assumptions of primate evolution.

Genetic studies suggest that humans and great apes split from a common ancestor about eight million years ago, but paleontologists have struggled to find fossils for the ancestors of modern African great apes for the past 13 million years. However scientists found plenty of fossil evidence for great apes in Europe and Asia during that period and they also noted some similarities between some of those apes and contemporary African apes.

That led some paleontologists to speculate that the common ancestor of apes and humans had left Africa, and evolved into several different species, and that one of those species later returned to the continent to become the missing link between man and his closest primate relatives.

But the new evidence appears to undercut that theory, and it doesn’t stand alone.

In addition to the new Kenyan species of ancient ape, (dubbed Nakalipithecus nakayamai,), evidence recently emerged of another ancient African ape.

In August, a team of Japanese and Ethiopian paleontologists announced that they had uncovered 10-million year-old teeth fossils in Ethiopia’s Afar region in 2006 and 2007. The scientists said the teeth probably belonged to a “proto-gorilla” species which they named Chororapithecus abyssinicus.

Prior to this, the last time a hominoid fossil of this period was found in Africa was in Kenya in 1982.

The evidence that Africa was home to a number of ape ancestors in the middle to late Miocene period casts doubt on the theory that the ancestors of contemporary African apes were extinguished completely on the continent and were re-introduced from Europe or Asia, the authors wrote in the paper in the journal, Proceedings of the National Academy of Sciences.

And while it will require further fossil discovery to flesh out the family tree of modern African apes, “it is likely that these early Late Miocene African hominoids are more or less close to the last common ancestor of the African great apes and humans,” the authors said.