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Ancestral Handful: Tiny skull puts Asia at root of primate tree

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9:08am, December 23, 2003
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Researchers have unearthed the partial skull of the oldest known primate, a teeny creature that lived in south-central China 55 million years ago.

The discovery extends the geographic reach of the ancient genus Teilhardina into Asia, say Xijun Ni of the Chinese Academy of Sciences in Beijing and his coworkers. Until now, all Teilhardina fossils had been teeth and jaw fragments from North America and Europe.

Teilhardina belonged to the tarsierlike omomyids that lived 55 to 36 million years ago. They were precursors of today's tarsiers, monkeys, apes, and people.

The newly found fossil derived from an animal that was smaller than any living primate. Weighing about 1 ounce, it would have fit in the palm of a person's hand. The creature's size and sharp teeth peg it as an insect eater, the scientists report in the Jan. 1 Nature.

The fossil's forward-looking eye sockets are also revealing: They're much smaller relative to skull length than those of any other omomyid specimen. Living primates with small, forward-facing eyes are generally diurnal, staying active during the day and sleeping at night. This raises the surprising possibility that Teilhardina originated in Asia as a diurnal primate, but that its descendants evolved into large-eyed, nocturnal animals.

"That's not at all what I expected," remarks paleontologist Richard F. Kay of Duke University Medical Center in Durham, N.C. The finding suggests that the first primate ancestor may have been diurnal, too, he says.

K. Christopher Beard of the Carnegie Museum of Natural History in Pittsburgh, who specializes in Asian primate fossils, calls the new find a "landmark discovery." It shows that ancient primate evolution proceeded with twists, rather than in a straight line, toward apes and people, he says.

Or maybe not. Although the Asian Teilhardina find comes from a primate that lived near the time of omomyid origins, this ancient creature could have been nocturnal, as has been traditionally assumed, says paleontologist Robert D. Martin of the Field Museum in Chicago in a commentary published with the new report. In particular, he notes, the fossil contains a large opening on the snout to accommodate a nerve for the whiskers. Such a large opening is common among nocturnal mammals.

The Asian find casts doubt on the argument that 55-million-year-old fossils recently found in Wyoming came from a close primate relative of the ancestor of modern monkeys, apes, and humans (SN: 12/21&28/02, p. 399: Available to subscribers at New fossil weighs in on primate origins). This genus, Carpolestes, differed substantially from Teilhardina. The North American creature had relatively large, side-facing eyes and ate primarily fruit. Kay suspects that Carpolestes actually belonged to a line of nonprimates that evolved some primatelike features.

The new find supports the theory that ancient Teilhardina species migrated back and forth between Asia and Europe 55 million years ago, at a time when waterways from the north and south split Eurasia vertically down the middle, Martin adds.

In contrast, Beard theorizes that Teilhardina migrated from Asia across land bridges to North America and then to Europe. Africa became central to primate evolution only after this intercontinental trek, he contends.

Kay doesn't discount Africa as the place where primates first arose. "But the fossil evidence for Asia is growing," he says.

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