Researchers have discovered a 10-million-year-old jaw bone in Kenya 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 in 2005 along with 11 teeth in volcanic mud flow deposits in Kenya's northern Nakali region.
The species -- somewhere between the size of a female gorilla and a female orangutan -- may prove to be the "missing link" in the evolution theory, 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," said Frederick Manthi, Senior Research Scientist at the National Museums of Kenya.
"We have to find more fossils from a cross-section of sites to sustain that particular theory," he told a news conference.
Christened Nakalipithecus nakayamai, the new species fed on nuts, seeds and fruit.
"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.
Kunimatsu said it was hard to determine what Nakalipithecus nakayamai looked like.
"We only have some jaw fragments and some teeth ... but we hope to find other body parts in our future research. We plan to go back next year. We will try to find bones below the neck to tell us how the animal moved," he said.
Published in the latest issue of the Proceedings of the National Academy of Sciences, the finding is significant as it gives credence to the theory that the evolution from ape to man may have taken place entirely in Africa.
Prior to this finding, there had been so little fossil evidence in Africa dating between 7 to 13 million years ago that some experts began to surmise that the last common ancestor left Africa for Europe and Asia, and then returned later.
But Kunimatsu said the findings suggested that the ancestor of African great apes and humans likely evolved in Africa.
"Now, we have a good candidate in Africa. We do not need to think the common ancestor came back from Eurasia to Africa. I think it is more likely the common ancestor evolved from the apes in the Miocene in Africa," he said.
The Miocene is a period of time extending from 23.03 million to 5.33 million years ago.
"Some apes (then) left Africa and migrated to Eurasia. They then became orangutans in Southeast Asia. Today's orangutan evolved from the apes that left Africa," he said.