Fossil hunters exploring the eastern edge of the Rift Valley of Kenya have found the jawbone of a 10-million-year-old ape that appears to be a close relative of the last ancestor of humans, chimpanzees, and gorillas. The discovery of this ancient ape strikes a new blow against a theory that apes in Africa died out millions of years ago only to be replaced by other apes that had migrated to Europe and Asia and then returned.
The ancestors of humans and chimpanzees split about 5 million to 7 million years ago, according to recent genetic studies. Verifying that date in the fossil record has been difficult, however, because the trail of old bones for apes goes cold in Africa right at the time when the African apes were diverging 7 million to 12 million years ago in the middle-to-late Miocene epoch. Given the paucity of data, some researchers have proposed that apes originated in Africa but went extinct there. According to the theory, today's African apes descended instead from those that migrated to Europe or Asia and eventually wandered back to Africa. Now, an international team of researchers is reporting the discovery of a new species of extinct ape in Kenya, making it the second large-bodied ape discovered recently in Africa from this critical time. Its existence casts more doubt on the "Out-of-Europe" theory of ape evolution.
Yutaka Kunimatsu, a paleoanthropologist at Kyoto University in Japan, and colleagues discovered the new species in Nakali, Kenya, in 2005. The researchers recovered the partial lower jaw and 11 teeth of an ape, dubbed Nakalipithecus nakayamai, which lived almost 10 million years ago, they report online today in the Proceedings of the National Academy of Sciences. They found the new species less than 30 kilometers from the Samburu Hills where another large-bodied ape, Samburupithecus kiptalami, which lived 9.6 million years ago, was discovered years ago. "The discovery of Nakalipithecus shows that there were two different large hominoids even within a very narrow range of time and space in the early late Miocene of Kenya," says Kunimatsu. Unlike S. kiptalami, which many researchers think was not directly related to humans or chimps, the new fossil has traits that suggest it was a close relative of the last common ancestor of humans, chimps, and gorillas. It also comes hot on the heels of the discovery of another ape that lived at about the same time in Ethiopia, Chororapithecus abyssinicus, whose teeth closely resemble those of modern gorillas (Science , 24 August, p. 1016).
Taken together, these finds suggest that once apes originated in Africa at least 22 million years ago, they never left--although some did migrate to Europe and Asia, where they flourished. "This specimen forms yet more evidence that there was a flourishing and diverse population of apes in the late Miocene of Africa and further erodes the Out-of-Europe notion," says paleoanthropologist Andrew Hill of Yale University. Hill suggests that the gap in the fossil record for Miocene apes in Africa may exist because few people have looked for apes in the right time and place in Africa--or that many of the apes lived in wooded habitats where their remains were less likely to fossilize in acidic soils.