Experts find jawbone of pre-human great ape in Kenya

By Katie Nguyen

NAIROBI (Reuters) - Researchers unveiled a 10-million-year-old jaw bone on Tuesday they believe belonged to a new species of great ape that could be the last common ancestor of gorillas, chimpanzees and humans.

The Kenyan and Japanese team found the fragment, dating back to between 9.8 and 9.88 million years, in 2005 along with 11 teeth. The fossils were unearthed in volcanic mud flow deposits in the northern Nakali region of Kenya.

The species -- somewhere between the size of a female gorilla and a female orangutan -- may prove to be the "missing link", the key step that split the evolutionary chains of humans and other primates, Kenyan scientists said.

"Based on this particular discovery, we can comfortably say we are approaching the point at which we can pin down the so-called missing link," Frederick Manthi, senior research scientist at the National Museums of Kenya, told reporters.

"We have to find more fossils from a cross-section of sites to sustain that particular theory," he added, speaking at a desk where the approximately four-inch sliver of bone was displayed alongside human and gorilla skulls.

It was the latest important finding in east Africa's Rift Valley -- a region long regarded as the "cradle of humankind".

"The teeth were covered in thick enamel and the caps were low and voluminous, suggesting that the diet of this ape consisted of a considerable amount of hard objects, like nuts or seeds, and fruit," Yutaka Kunimatsu at Kyoto University's Primate Research Institute said in a telephone interview.

"It could be positioned before the split between gorillas, chimps and humans," he added.