A newly found species small enough to fit in the palm of a hand is North America's oldest known primate, according to a new study.

Christopher Beard, a paleontologist at the Carnegie Museum of Natural History in Pennsylvania, recently discovered fossils of the 55-million-year-old creature on the Gulf Coastal Plain of Mississippi.

Named Teilhardina magnoliana, the animal is related to similarly aged fossils from China, Europe and Wyoming's Big Horn Basin.

"They are very, very primitive relatives of living primates called tarsiers, which live today in Southeast Asia," Beard says.

But the layer of rock in which the new fossils were found raises the controversial possibility that primates appeared in North America before their close relatives showed up in Europe, as previous studies had suggested, Beard adds.

A paper on the findings appears in the journal Proceedings of the National Academy of Sciences.

LAND BRIDGE CROSSING

The discovery suggests that Teilhardina primates migrated to North America across the Bering land bridge from Asia, Beard says. Then the creatures proceeded to Europe across an Atlantic land bridge that emerged thousands of years later.

Previous research had suggested the primates reached the Americas via a westward route instead, from Asia through Europe. But that path was submerged at the time the primates show up in ancient Mississippi, Beard says.

At that time, the world was undergoing an ancient global warming event known as the Paleocene-Eocene Thermal Maximum, or PETM.

Many scientists believe the PETM is analogous to what the world is experiencing today due to human-caused increases in greenhouse gases such as carbon dioxide.

Unlike today, however, there were no polar ice caps.

In fact, sea levels were falling as Earth's shifting landmasses opened up huge ocean basins.

T. magnoliana dates to a time before sea levels had fallen enough for primates to cross over to North America from Europe, Beard says.

"We know the sea level was high when our fossil primates lived in Mississippi, because the actual bed that yielded our fossils is a marine bed," he notes.

Most of the fossils at the site were shark teeth and similar objects.

The primate's skeleton, he says, likely washed into the shallow estuary from the coastline.

A second fossil bed in a higher layer was laid down by a river or stream, not an ocean, indicating that sea level continued to fall after the primate fossils were deposited, Beard adds.

The same sea-level imprints are found in the rock section where Teilhardina was found in Europe. This indicates that Teilhardina arrived there after the sea level had dropped.

"So we know the Teilhardina fossils we're finding in Mississippi are older than the ones that have been found in Europe and along with that they are anatomically more primitive," Beard says.

DATA QUESTIONED

Philip Gingerich is a paleontologist at the University of Michigan in Ann Arbor.

He argued in a 2006 PNAS study that ancient primates migrated to North America via Europe.

Gingerich's study was based largely on comparison of carbon isotope signatures from the fossil beds where the ancient primates were found in Europe, Asia and Wyoming. Scientists use the signatures to identify and date events within the PETM.

Beard acknowledges that his study lacks an appropriate carbon isotope signature.

Gingerich says the missing data makes Beard's claims impossible to validate. Sea level rose and fell several times during the PETM, making geologic markings difficult to interpret, Gingerich adds.

"We're talking about events here that could be separated by as little as 10 (thousand) or 15 (thousand) or 20 thousand years," he says.

But though Beard has been unable to find the carbon isotope record at his site in Mississippi, he says he has found an aquatic micro-organism that is associated with the record.

That, combined with the other geologic evidence, makes him confident in his result.

TROPICAL CLIMATE

T. magnoliana is best suited to live in hot, muggy climates, Beard adds.

So scientists can infer that even the northern reaches of North America were forested, warm and wet when these creatures migrated across the Bering land bridge, Beard says.

If T. magnoliana indeed predates the Teilhardina find in Wyoming, it would also indicate the primates stuck to the coasts for tens of thousands of years before the climate changed enough for them to migrate inland.

"It took time for the North American ecosystems, especially in the interior part of the continent, to kind of adapt to this big warming event," Beard says.

National Geographic

Copyright 2008. All rights reserved by New York Times Syndication Sales Corp. This material may not be published, broadcast or redistributed in any manner.