A fossil unearthed in Kenya belongs to a new species of ape that lived around the same time as the last common ancestor of gorillas and humans.
The 10-million-year-old jawbone and 11 teeth were discovered in volcanic mud flow deposits in Kenya's Nakali region.
Dubbed Nakalipithecus nakayamai, the new species supports the idea that the ancestors of gorillas, chimpanzees and humans evolved exclusively in Africa, the researchers say.
[The human-gorilla split is thought to have occurred about 2 million years earlier than the human-chimp split, though exactly how long ago each took place is fairly fuzzy. Genetically, chimps are closer to humans than they are to gorillas.]
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A competing hypothesis states that the last common ancestor of both groups descended from a repatriated hominid that left Africa around 16.5 million years ago for Europe or Asia, but then returned about 9.5 million years ago after one branch split off to give rise to the orangutans of southeast Asia.
Todd Disotell, an anthropologist at New York University who was not involved in the recent discovery, called the new fossil a "great find," but said it is too inconclusive to draw major conclusions from.
"It could well be a Eurasian immigrant," Disotell told LiveScience.
The new fossil is detailed in the Nov. 12 issue of the journal Proceedings of the National Academy of Sciences.
N. nakayamai is estimated to have lived around 9.9 million to 9.8 million years ago.
Its dental features resemble those of Ouranopithecus macedoniensis, an ape that lived in what is now Greece between 9.6 million and 8.7 million years ago and which some scientists think is the last known common ancestor of African great apes, including humans.
Because both N. nakayamai and O. macedoniensis are only known from jawbone fragments and teeth, scientists can say little more about their appearance or behaviors than that they likely ate hard foods.
"Imagine that you are given some human teeth and asked to tell what the person with those teeth looked like," said study team member Yutaka Kunimatsu of Kyoto University in Japan. "Is the skin of the person black or white or intermediate in color? Is the person tall or short? Fat or slim? Did they have blue eyes or black eyes?"
Back to Africa
David Begun, an anthropologist at the University of Toronto who was also not involved in the study, called N. nakayamai a "very interesting and important discovery," but said it doesn't change his view that the ancestors of African great apes and humans spent some of their time evolving outside of Africa.
"Both these researchers and I agree that the last common ancestor of African great apes and humans came from Africa," Begun said in an e-mail interview.
According to Begun's hypothesis, the early ancestors of African apes and humans initially left Africa for Europe in search of more seasonal fruits, but some 7 million years later their descendants returned.
Back in Africa, the hominids continued their evolution, where they eventually gave rise to gorillas, chimpanzees and humans.
"But the events that led to the divergence of Asian and African ape lineages happened in Europe at least 2 million years before the [N. nakayamai] came into existence," Begun said.
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