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Fossils of Tiny Primates Found
By DAVID KINNEY
Associated Press Writer

MARCH 16, 2000 - Some ancestors of monkeys, apes and humans were so tiny that they could have stood atop a person's thumb — a new finding astonishing even to anthropologists.

Fossilized foot bones from two species smaller than any other known creature on the primate family tree were found at a limestone mine in eastern China. The bones are each about the size of a grain of rice.

"This discovery reinvents our definition of what the primate order is all about and how it arose,'' said Richard Stucky, curator at the Denver Museum of Natural History. He said he was "almost at a loss for words.''

At one-third of an ounce — the weight of a couple of pencils — the smaller of the two species is dwarfed by the 1-ounce Madagascar mouse lemur, the smallest known primate alive today. The two lived in a rain forest about 45 million years ago, feeding on insects and sap.

Scientists from Carnegie Museum of Natural History, Northern Illinois, Northwestern and the Chinese Academy of Sciences in Beijing detail the species in this week's Journal of Human Evolution.

In a separate article in the journal Nature, the group reported on more fossils from a previously discovered third primate called Eosimias centennicus. They had discovered its teeth and jaws in the mid 1990s. Now they've got ankle bones, which they say backs up their controversial claim that Eosimias is an early ancestor of humans.

Eosimias and the two new tiny species all lived together around the time when lower primates split from the higher primates.

Lower primates include lemurs. Higher primates include humans. The split happened 40 million to 50 million years ago.

At 3 ounces, Eosimias was larger than the tiny species, which have not been named.

The smaller of the two new species might have been below Eosimias on the evolutionary branch, a common ancestor of higher primates and some lower primates, said Chris Beard of the Carnegie Museum.

The larger one — weighing half an ounce — appears to be a higher primate, perhaps in the same family as Eosimias.

"Nobody would have believed that as recently as 45 million years ago, our ancestors were about the size of a shrew,'' Beard said.

Anthropologists expected to find a smallish creature at the fork between higher and lower primates.

Because it would have needed to eat insects voraciously to keep up with an overheated metabolism, it would have had higher primate features: two eyes facing forward and soft hands without claws, all the better to focus on and grab bugs.

"That said, these are really tiny,'' said Brian Richmond, a George Washington University researcher.

Unlike modern higher primates, which are social and move about in the daytime, these creatures' tiny size would have forced them to hide during the day and feed at night.

The tiny species are the smallest of 12 to 16 species of little primates found at the Chinese mine.

Eosimias is among them. Its ankle bones are further proof the creature was a higher primate, Beard said. It apparently walked on all fours, because like monkeys that scurry atop tree branches, their feet faced downward. Lower primate cling to tree trunks, so their feet face inward.

But the evidence of Eosimias' status as a higher primate is still not conclusive. Richmond said it is possible Eosimias was a lower primate that evolved a few characteristics similar to higher primates.

Also, Beard's team has not found a skull or full skeleton. They inferred the ankle fossils to be Eosimias' based on where they were found.

Stucky is convinced, calling it "significant, additional evidence'' that Eosimias is a higher primate.

 
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