Among the rarest mammals in Southeast Asia, the kouprey's discovery almost 70 years ago in the jungles of Cambodia stunned the scientific community and led to a decades-long campaign to save it from extinction.

But what if this elusive forest ox wasn't a natural species after all?

That is the controversial premise raised by Northwestern University biologist Gary Galbreath and his colleagues F.H. Weiler and J.C. Mordacq in a paper published in April in the Journal of Zoology.

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Galbreath and his team compared the DNA from two kouprey skulls — something previously impossible because of technological limitations — with that of the Cambodian banteng, a semi-domesticated species of cattle, and found they were similar.

They concluded that the kouprey, which may well be extinct, most likely originated as a hybrid bred from domestic banteng and zebu cattle in Cambodia a century ago and only later became wild, rather than arising in the wild as a natural species.

"The kouprey has acquired a rather romantic, exotic reputation," said Galbreath, associate director of Northwestern's Program in Biological Sciences in Evanston, Ill. "Some people would understandably be sad to see it dethroned as a species."

The paper stirred up wild cattle specialists who have spent decades trying to save the kouprey. They say the conclusion was hasty and based on insufficient data.

The kouprey, a nomadic ox with dramatic curved horns that resembles a water buffalo, was first identified in 1937 as a new species. It was discovered in the forests of Cambodia, but scientists believe its range at one time stretched into parts of Vietnam, Laos and Thailand.

Conservationists ever since have led a frustrated campaign to save the kouprey.

American zoologist Charles Wharton failed in the 1960s to capture the beasts — two died and three escaped — as part of a project to raise them in captivity in Texas.

A proposal by three Asian governments in the 1980s to export frozen kouprey embryos to U.S. zoos never advanced because no one could find any of the animals.

The last confirmed sighting by a Western scientist was in the 1960s. Civil wars in Cambodia during the 1970s and 1980s kept conservationists out of the country, and more recent searches failed.

Among the most infamous searches was one in 1993 led by American journalist Nate Thayer, who took an elephant caravan that included former Khmer Rouge guerrillas, an American mercenary and the publisher of Soldier of Fortune magazine.

They spent a fruitless two weeks looking for the ox, which grows to a height of about 6½ feet and weight of 1,300 to 2,000 pounds.

"We never found the kouprey, but did come across Khmer Rouge soldiers who spotted us and fled, presumably to inform their commandeers of a group of white guys heavily armed in the area," Thayer said in an e-mail message.

Weiler, who took part in the DNA study with Galbreath, also led several unsuccessful expeditions in Cambodia from 1997 until last year. He hired elephant and tiger trackers and interviewed nearly 300 people to get leads.

Despite vivid stories of the beast in the jungle, he never saw one.

"I came to the conclusion that the kouprey is extinct," Weiler said. "I've closed the book. It's possible three or four will pop up somewhere. But it's highly unlikely."

Not everyone agrees. The World Conservation Union still designates the kouprey as critically endangered and estimates there are less than 200 left in remote parts of Indochina.

"I think it's a little too early to give up hope. It is hard to prove something is extinct," said Simon Hedges, a wild cattle expert. "When you consider that new species are still being discovered in Indochina, I don't think it's entirely unrealistic to believe there might be pockets of species such as the kouprey living in the same area."

More controversial is the suggestion by Galbreath and his team that the kouprey should never have been listed as a species in the first place, theorizing it was likely bred as a domestic hybrid "to produce a strong animal that survives in difficult circumstances."

Calling it the most likely explanation based on the DNA testing, the animal's limited geographic range and its physical similarities to domestic cattle, Galbreath said that "it is surely desirable not to waste time and money trying to locate or conserve a domestic breed gone wild."

"The limited funds available should be used to protect wild species," he said.

But Galbreath has done little to change long-standing opinions among kouprey enthusiasts.

Alexandre Hassanin, a French scientist who along with Anne Ropiquet announced in 2004 that they had sequenced the kouprey DNA to show it was a natural species, said he disagrees with the paper.

The Cambodia government, which in the 1960s designated the kouprey as its national animal, has no plans to change that status.

"In my view, those researchers are not so sure either. If it was a hybrid, when did that happen?" said Yim Voeuntharn, Cambodia's deputy minister of agriculture. "There is no specific evidence."

Hedges, the wild cattle expert, calls Galbreath's findings "premature" and "counterproductive," saying it is wrong to discount the kouprey as a species based on such a small sample of DNA.

"If their analysis shows anything, it is that there are some hybrid banteng with kouprey ancestry," he said. "They don't show anything beyond that. They are arguing on very little information that the kouprey is a feral relic."

Galbreath agrees more DNA testing is needed and plans to take samples from banteng in other parts of Southeast Asia.

"For half a century, biologists have been complacent about this," he said. "Everyone fell in love with the idea that the kouprey was a natural species."