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Fossils reveal primate history: jaws and teeth shed light on ape-monkey split.

The oldest known fossils of an ape and a monkey have been uncovered, providing an intriguing glimpse of a crucial time in primate evolution.

The discoveries are controversial but suggest that by 25 million years ago, two major primate groups were distinct: one that today includes apes and humans and another that encompasses Old World monkeys such as baboons and macaques. Previous studies using living primates' DNA suggested that ancient apes and Old World monkeys parted from a common ancestor between 25 million and 30 million years ago.

The new fossils, from Tanzania's Rukwa Rift Basin, suggest that the evolutionary split between these primate lines must have occurred close to 30 million years ago, or perhaps even earlier, anthropologist Nancy Stevens of Ohio University in Athens and her colleagues conclude May 15 in Nature.

Fossil finds since the 1800s have revealed that dozens of ape species inhabited Africa, Asia and Europe between 22 million and 5.5 million years ago. Fewer fossils of Old World monkeys have been found, but a handful of monkey species are known to have inhabited Africa around 20 million years ago.

"The period from 25 million to 30 million years ago is the least-sampled interval in primate evolutionary history, with only three fossil primates known before our discoveries and five known now," Stevens says.

Her team assigns a tooth-bearing lower right jaw to a new ape genus and species, Rukwapithecus fleaglei. The scientists classify a second find, a jaw fragment containing a tooth, as a new monkey genus and species, Nsungwepithecus gunnelli. These animals lived 25.2 million years ago, based on age estimates of volcanic ash layers that sandwiched the Tanzanian fossils.

The new report "makes a strong case that Old World monkeys and apes had already diverged 25 million years ago," says K. Christopher Beard of the Carnegie Museum of Natural History in Pittsburgh.

But New York University anthropologist Terry Harrison disagrees. The new Rukwapithecus jaw joins a cluster of fossils from African primates that probably did not evolve into apes, he says.

The tooth-and-jaw piece attributed to a monkey may instead come from an ancient form of pig or peccary, Harrison adds. In his view, the researchers need more fossils to tell whether the animal is even a primate.

Caption: A tooth-bearing lower right jaw found in Tanzania may come from the oldest known ape, which lived 25 million years ago.


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Author:Bower, Bruce
Publication:Science News
Geographic Code:6TANZ
Date:Jun 15, 2013
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