From: Allison Winter, ENN
Published June 12, 2013 09:47 AM

New fossil shines light on primate and human evolution

A 55 million year old fossil that has been unearthed from an ancient lakebed in China's Hubei Province has revealed a pivotal event in primate and human evolution.

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Hailing from the early Eocene Epoch, the fossil is crucial to the branch split that led to anthropoids (monkeys, apes, and humans) on one side, and living tarsiers (small, tree-dwelling nocturnal primates) on the other.

The discovered fossil represents a previously unknown genus and species named Archicebus Achilles.

"Archicebus differs radically from any other primate, living or fossil, known to science. It looks like an odd hybrid with the feet of a small monkey, the arms, legs and teeth of a very primitive primate, and a primitive skull bearing surprisingly small eyes", says Dr. Christopher Beard of the Carnegie Museum of Natural History in Pittsburgh and one of the research authors.

Archicebus is 7 million years older than the oldest fossil primate skeletons previously known. Yet Archicebus belongs to a separate branch of the primate evolutionary tree that lies much closer to the lineage leading to modern monkeys, apes and humans. According to Dr. Xijun Ni of the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) at the Chinese Academy of Sciences in Beijing, "Archicebus marks the first time that we have a reasonably complete picture of a primate close to the divergence between tarsiers and anthropoids. It represents a big step forward in our efforts to chart the course of the earliest phases of primate and human evolution."

The team of scientists was able to reconstruct the fossil by using virtual three-dimensional data, acquired on the European Synchrotron Radiation Facilty's (ESRF) ID17 beamline. "For several years the ESRF has developed imaging facilities enabling us to non-destructively study fossils still buried in rock with a level of details and contrast unique in the world. We've been able to reveal microstructures that would normally require partial destruction of the specimens. 3D scans allow us to virtually make the skeleton "stand up"", says Paul Tafforeau from the ESRF X-ray imaging group.

Archicebus is thought to have weighed about 20-30 grammes (0.04-0.06 pounds) and be smaller than today's smallest living primates. This overturns earlier ideas suggesting that the first members of the anthropoid lineage were as large as today's modern monkeys.

The scientific paper was published last week in the journal Nature.

For more information see EurekAlert and ESRF.

Archicebus Achilles image credit CAS/Xijun Ni.

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