Tuesday, December 30, 2008

Oldest cheetah fossil found, points to Asian roots?

Rebecca Carroll
for National Geographic News

December 29, 2008

The earliest known cheetahs roamed present-day China more than two million years ago, according to new research.

The study supports the theory that the big cats originated in the Old World, not North America.

The new idea is based on the discovery of a new species of prehistoric cheetah. A nearly complete fossil cranium of the new species, found in China's Gansu Province, is similar in size and shape to modern cheetah skulls, researchers found.

But some of its teeth are extremely primitive, said study co-author Ji H. Mazák of the Shanghai Science and Technology Museum.

This "mosaic of anatomical features" suggests the Chinese cheetah, called Acinonyx kurteni, represents an early stage in cheetah evolution, he said.

The varied traits also indicate skull and dental characteristics considered unique to cheetahs evolved gradually, according to the study published today in Proceedings of the National Academy of Sciences.

Throwing a potential wrench in the new discovery, other scientists say they had already identified the species under another name.

All American?

The Cheetah, the fastest land animal, is a highly threatened species with an estimated adult population of only 7,500, according to the International Union for Conservation of Nature (IUCN).

The only known wild cheetah population outside of Africa is a critically endangered group of fewer than a hundred in Iran.

But cheetah fossils throughout Africa, Europe, Asia, the Indian subcontinent, and even North America have been found between 3.2 million and 2,000 years old.

The newly studied fossils were dated to the late Pliocene, between 2.15 and 2.55 million years ago.

Two prehistoric cheetah-like species of North America are believed by some scientists to be distant cousins of giant cheetahs of ancient Europe.

This possible relationship has led some researchers to speculate that the earliest cheetahs may have originated in North America and traveled across the Bering Strait from Alaska to Siberia.

Intercontinental Travel?

Mazák said the new finds challenges this theory, suggesting instead a Eurasian-African origin of the cheetah lineage.

For instance, the primitive dental features would have been more developed in the Chinese fossil if cheetahs had come from North America.

This leaves the question of whether cheetahs traveled across the Bering Strait the other way—from Siberia to Alaska—or if the American cheetah-like cat evolved separately, as some scientists argue.

By Any Other Name?

Deng Tao, a professor at the Chinese Academy of Sciences in Beijing, was "astonished" reading the new study.

The newly identified skull is from a new species, he said.

Deng said his team had already described this species as Sivapanthera linxiaensis. Sivapanthera is the fossil genus of the ancient cheetah—today's cheetahs belong to the Acinonyx genus.

Mazák responded that his team and Deng's team had studied different species. He argued that Deng's fossils more closely resembled the genus Panthera—which includes the tiger, leopard, jaguar and lion—than Acinonyx.

Deng's fossils were also too big to belong to a cheetah species, Mazák added.

Deng also claimed that the skull in the new study was not an intact original, but rather a compilation from bones of various individuals and possibly even various species.

The difference between an intact skull and a compilation is apparent from comparisons of the photos of the skull in the current study and the skulls his team studied, Deng said.

Mazák denied this charge, saying his team had carefully examined their cranium and determined that all of its parts—including teeth—belonged to the same individual.



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