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Tanya Lewis, LiveScience Staff WriterDate: 15 May 2013 Time: 01:00 PM ET 



Artist's reconstruction of two new Oligocene primates, the ape Rukwapithecus (foreground left) and the Old World monkey Nsungwepithecus (background right).
CREDIT: Mauricio Antón


The oldest ape and Old World monkey fossils have been unearthed in a riverbed in Tanzania, a new study reports.

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"These discoveries are important because they offer the earliest fossil evidence for either of these primate groups," said lead study author Nancy Stevens, an anthropologist at Ohio University in Athens, Ohio.

DNA evidence has long suggested that apes and Old World monkeys diverged from a common ancestor between 25 million and 30 million years ago. But until now, no fossils older than 20 million years had been found.

The age of the new specimens extends the origin of apes and Old World monkeys into the Oligocene Epoch, which lasted from 34 million to 23 million years ago. Previously, only three primate species were known from the late Oligocene globally, Stevens said.

"These finds can help us to further refine hypotheses about the timing of diversification of major primate groups," Stevens said.

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The fossils themselves are only fragments, but they nonetheless provide important information about evolutionary relationships, Stevens said. The Nsungwepithecus fossil is a jaw fragment containing a lone molar tooth, whose shape and other dimensions suggest it came from a species related to other early cercopithecoids. Rukwapithecus had a more complete partial jaw containing one premolar and three molars; preliminary analysis suggests they came from hominoids in the nyanzapithecine group.

Rukwapithecus would have weighed about 26 lbs. (12 kilograms), the researchers estimate. Because Nsungwepithecus is so fragmented, its size is harder to estimate, but it would probably have been slightly smaller than Rukwapithecus, Stevens said. -- http://www.livescience.com/

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