Scientists have announced the discovery of the world's oldest known fossil primate skeleton, which suggests the early ancestors of humans might be "miniscule monkeys" smaller than rats.

The nearly complete skeleton, unearthed in central China's Hubei Province in 2003, belongs to a new genus and species named Archicebus achilles, according to a paper co-written by Chinese, American and French scientists and published in Thursday's issue of the journal Nature.

Scientists said the monkey lived 55 million years ago, during the early part of the Eocene epoch. It is 7 million years older than the oldest primates known previously, including Darwinius from Messel in Germany and Notharctus from Wyoming in the United States.

The tiny primate had a body around 71 mm long and its weight was estimated between 20 and 30 grams. Studies into its skeleton suggest the creature was a frequent leaper favoring four-limbed grasp-leaping, and its small eyes and pointy teeth indicate it was an insect-hunter only by day.

Dr. Ni Xijun of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences, who led the research team, said the primate was an early member of the tarsier family but one very close to anthropoids, which include monkeys, apes and humans.

"It lies close to the root of the primate phylogenetic tree, where the lineages of tarsiers and anthropoids have just begun to diverge, which explains why it bears traits of both tarsiers and anthropoids," Ni said in an exclusive interview with Xinhua.

Ni said the discovery of the new primate offered clues to the evolutionary roots of higher primates, or anthropoids, and illustrated the life of human's farthest ancestors.

"Odd hybrid"

The fossil was unearthed from an ancient lakebed near the city of Jinzhou, near the course of the modern Yangtze River.

Scientists from the three countries spent ten years comparing more than 1,000 anatomical characters of 157 mammals to determine the fossil's position in the primate family tree.

Dr. Christopher Beard, paleontologist at the Carnegie Museum of Natural History in Pittsburgh and co-author of the article, described the new species as differing radically from any other primate 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," Beard said, and unlike others in the tarsier family distinguished by their enormous eyes, the primate had "surprisingly small eyes."

Most living or fossil tarsiers have big eyes as they are nocturnal creatures relying mainly on vision when foraging. The small eyes of the new primate suggest it preyed in the day like an anthropoid, Ni said.

"There is a saying that 'anthropoids have walked from darkness to light,' but our study suggests the earliest primates were never 'night owls'," Ni said.

The fossil takes its name from the Greek arche, meaning beginning or first, and the Latin cebus, meaning long-tailed monkey. The species name achilles derived from the mythological Greek warrior Achilles, highlighting the creature's unusual heels. ( "Its feet were very long, even longer than its lower legs. But it had short and wide heels, which is one defining character of anthropoids," Ni said.

Scientists said the primate lived during a period of global "greenhouse" conditions, when much of the world was shrouded in tropical rainforests. Anatomy into its feet suggest the primate was adept at tree climbing and leaping.

"It can grasp the branch using its feet when performing a jump, so its hands were freed for performing other motions, like seizing a bug," Ni said, adding that this might have laid the biological basis for evolution of higher primates toward walking upright.

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