Oldest Primate Fossil: Is Archicebus Achilles Earliest Human Link?

By iScienceTimes Staff on June 5, 2013 5:28 PM EDT

tarsier
A 55-million year old fossil belonging to a tiny tree dweller, Archicebus achilles, is thought to be one of humans' earliest ancestors. Pictured here is a tarsier, which comes later than Archicebus achilles in the evolutionary line. (Photo: Flickr: goodspeed)

A 55 million-year-old fossil belonging to a tiny tree dweller is thought to be one of humans' earliest ancestors. A study of the fossil, which was discovered in central China, was published in the journal Nature.

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The new species, Archicebus achilles, suggests that humans' ancestors were very small. It may have weighed as little as 20 or 30 grams -- that's about the weight of five U.S. quarters. It was 2.8 inches long.

According to the researchers, Archicebus is part of the evolutionary line leading to tarsiers, small arboreal animals only found in Southeast Asia. But the Archicebus is far older, and so it is believed to be at the base of the lineage of a "sister" group of major interest: anthropoids. That's a primate group that includes things like monkeys, apes ... and humans.

"It's a close cousin in fact," said study author Christopher Beard, of the Carnegie Museum of Natural History in Pittsburgh. He called Archicebus "the closest thing we have to an ancestor of humans" from such a far back time period.

Beard also said of the discovery, "For the first time, it really shines a light on an important phase of primate and human evolution that we just had very little information about before."

"It's a cute little thing; it's ridiculously little," Beard said. "That's one of the more important scientific aspects of the whole story."

Like elephants, Beard said, the further back you go in time for some of today's massive mammals, the smaller they get. Archicebus was small and warm-blooded, constantly moving around and eating bugs to keep alive.

"[Archicebus were] very frenetic creatures," Beard said, "anxious, highly caffeinated animals running around looking for their next meal."

The scientists found the Archicebus in an ancient lake, at a site called the lower Eocene Yangxi Formation, in the Jingzhou area. They were lucky to find such an intact fossil, which was covered up with mud that hardened and preserved the fossil.

A decade-long analysis of the fossil, using high-res scans, meant that the scientists were able to extract an incredible wealth of information from the one fossil.

"This is really fantastic, impressive work," said Zhe-Xi Luo, a vertebrate paleontologist at the University of Chicago in Illinois. "Every detail that can be extracted from these fossils has been extracted."

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