Last October, in a remote Tibetan valley where few explorers had ever ventured, French anthropologist Michel Peissel and his team came across a strange-looking pony.

"When I first saw this odd little thing, I thought it was terribly ugly and I thought it might be a freak," the explorer said in an interview here. "Then a few more appeared. We saw dozens of them. We looked closely and realized it must be a breed. And then it struck me as archaic, like those in cave drawings."

Indeed, with its triangle-shaped head, straight nose and slanted eyes, the Riwoche horse -- named after the valley in which it lives -- bears a striking resemblance to horses depicted on the walls of the recently discovered Chauvet caves in the South of France, which date from 30,000 years ago.

"And see this tiny little rump?" Peissel said as he showed a picture of the pony and of the cave drawings. "It's the same. Other horses have long hindquarters."

The Riwoche horse's coarse beige coat, short black mane and black-striped spine also are features that equine specialists associate with prehistoric breeds.

Until now, Przewalski's horse, a primitive breed found in the 1880s on the border of Mongolia and Chinese Turkistan and now reduced to a few individuals, was the only breed thought to be especially similar to those in Stone Age cave drawings. Peissel said it is a much larger animal than the Riwoche horse, and has a heavy jaw and crooked nose.

Blood samples from the Riwoche horse are being tested at the Royal Agriculture College in Cirencester, England. "I think it will turn out to be a very important find," said Spanish veterinarian Ignasi Casas, an equine specialist who was a member of the expedition. "We still need to wait for the DNA results to see which place in evolution it belongs, but I think it's one of the first horses." That is, the DNA sequences of certain genes from the Riwoche horse may indicate that it has changed less than other breeds since true horses first appeared on Earth.

The evolution of the horse began about 55 million years ago in North America with a two-foot-tall creature called Hyracotherium (formerly known as Eohippus or "dawn horse.") It is believed that zebras, rhinos, tapirs, donkeys and horses are all descendants of Hyracotherium. The earliest fossils of modern horses, which belong to the genus Equus, were found in North America and date from about 4 million years ago. Starting about 2.6 million years ago, species of the Equus genus appeared in the Old World and in South America. In Africa and the Middle East, some species diversified into zebras and asses. The ancestors of the true horse (Equus caballus) spread across Europe, the Middle East and Asia. By the time the artist of the Chauvet caves painted animals on the cavern walls, about 30,000 years ago, the horses roaming what is now southern France were probably genetically quite similar to horses of today.

Horses were domesticated about 5,000 years ago. Some archaeological evidence suggests they were first ridden as early as 5,700 years ago on the Asian steppes, in an area just north of the Black Sea. They became extinct in North America, the birthplace of the species, about 2,000 years ago and were reintroduced from Europe by Spanish explorers.

Peissel pointed out that Tibet was one of the regions where horsemanship was mastered earliest.

"Tibet is the horse country par excellence," said Peissel. "Everybody thinks it's Mongolia for horses, but Tibet is seven centuries before Mongolia. They conquered all of Asia on horseback. They were the greatest horsemen, and their horses were the best horses in all of Asia."

Peissel has led 26 expeditions to Tibet, the Himalayan region that China has occupied since 1950. In 1964, he found the ruins of the lost kingdom of Mustang. Last year he discovered the source of the Mekong River, and, in 1993, the Nangchen horse, a breed with double the lung capacity of the average horse. While returning from an expedition to study the Nangchen horse in the Tibetan highlands last fall, the six-member team crossed one of the 16,000-foot passes into the 70-mile-wide Riwoche valley and saw the tiny horse grazing on the grassy slopes of the forest.

The Riwoche, which stands 12 hands (or four feet) tall, like a Shetland pony, is a tame horse used for riding and packing by the local people, a pre-Buddhist tribe called the Bon-po. When the horses are not working, the Bon-po let them roam freely in the valley.

Paleontologists said the discovery of the Riwoche horse may provide an opportunity to learn more about how horses have evolved since the Pleistocene, a period of intermittent ice ages that lasted from about 2 million years ago until about 10,000 years ago.

"If this is a relict of something that existed during the Pleistocene," said paleontologist John Rensberger of the University of Washington, "it {would} give us a living example of some of the diversity that existed {then}, for which we have only bones."

Malcolm C. McKenna, a vertebrate paleontologist at the American Museum of Natural History in New York, said the Riwoche horse might turn out to be a variant of Przewalski's horse, rather than a separate, primitive breed. Comparing its DNA to samples from Przewalski's horse and other modern breeds should help researchers place it on the horse family tree.

"I would imagine that 30,000 years ago, there were quite a lot of horses around that were similar to this," he said. The pony discovered in the Riwoche area of Tibet bears a striking resemblance to horses depicted in 30,000-year-old cave paintings, above. The Riwoche horse has the small rump, coarse beige coat and short black mane usually associated with prehistoric horses. It is about the size of a Shetland pony. CAPTION: Przewalski's horse ec CAPTION: Shetland pony ec CAPTION: Arabian ec CAPTION: Quarter horse ec CAPTION: Shire ec CAPTION: Comparative sizes of selected existing breeds.ec