Scientists have discovered the remains of a tree-climbing creature that lived 13 million years ago in what is now northeastern Spain and may be the last common ancestor of modern great apes and humans, according to a report published today.

Scholars greeted the discovery as a spectacular find that brings together 83 skull fragments, vertebrae, wrist bones, ribs and other bones from the same animal, a rarity in a field that often bases its analyses on a few skull fragments and teeth.

The fossil is also the oldest of a primate displaying traits shared by modern great apes, but not by monkeys: a broad, flat chest; shoulder blades fixed to the back rather than the sides; a spinal column suited to vertical climbing; a relatively flat face; and wrists that make it easy to grab and hold branches and tree trunks.

In all, the remains represent a landmark addition to a fossil record that seeks to trace primate evolution from a 55 million-year-old lemur-like creature to the monkeys and great apes -- chimpanzees, gorillas, orangutans and human ancestors -- and finally to the appearance of modern humans only 100,000 years ago.

"This fossil is a grandfather," said research leader Salvador Moya-Sola of Spain's Miguel Crusafont Institute of Paleontology. "It is a starting point -- the first fossil to show characteristics of a modern great ape."

But fellow paleontologists were cautious about recognizing the fossil as a "missing link" between apes and humans. Instead, they described it as one species on an evolutionary path to great apes -- but probably not the last one to be discovered.

"There are many, many links in the evolutionary chain, and this is one of them," said paleoanthropologist Carol V. Ward of the University of Missouri at Columbia. "This may be the last common ancestor between great apes and humans, or not. More likely not. But that ancestor is going to be a lot like this fossil."

Moya-Sola, speaking in a telephone interview from his institute office, said his team unearthed the fossil in a "small basin deposit" 20 miles outside Barcelona, naming it Pierolapithecus catalaunicus in honor of the nearby village of Els Hostalets de Pierola, in the province of Catalonia. The findings were published in today's issue of the journal Science.

The remains were of a tree-climbing male ape estimated to have weighed about 68 pounds, about the same size as the smallest of modern chimpanzees. Its teeth suggested the ape was a fruit eater, and it could probably have stood upright.

Many of the characteristics that define great apes are present in the new fossil -- broad chest, strong grip, and vertical climbing ability, but others are not. Moya-Sola noted that the ancient ape had small hands and fingers, the sign of a creature that can hop through the treetops but is unlikely to have been able to swing from branches.

The completeness of the find is unique: "Rarely do we get a skeleton along with the head, and this gives you vertebrae, and arm and leg bones," paleontologist Steven C. Ward (no relation to Carol) of the Northeastern Ohio Universities College of Medicine said in a telephone interview. "You can look at limb proportions, joints, body mass. This specimen is as good as everyone says it is."

Steven Ward, like Carol and other anthropologists, held out scant hope that the discovery would put to rest controversies surrounding the origin of the great apes, thought to have arisen between 11 million and 16 million years ago, and their spread throughout the continents of the Old World.

"It's maddening, because there are simply too many holes in the fossil record," Johns Hopkins University anthropologist Martin F. Teaford said in a telephone interview. "But if you can get a really good skeleton from 13 million years ago, it's a potential gold mine. That's exactly where you want to be."

Primates arose about 55 million years ago and apparently began to evolve into larger, less monkey-like forms between 25 million and 17 million years ago in Africa: "What you see is animals that we know are apes but walk around on all fours on branches like monkeys," Carol Ward said.

Great apes, by contrast, are too big to flit among the treetops and, through evolutionary time, acquired the ability to walk on two legs, climb tree trunks and swing from branches: "Fruit is out at the end of the branch, and if you weigh 300 pounds, you need to be able to grab more than one place," Carol Ward said.

Tracing the evolutionary process has proved difficult because about 16 million years ago, the primate fossil record in Africa "just petered out," Teaford said, only to pick up much later, when evidence of human evolution began to appear.

In the interim, the primate record reappeared in Europe and Asia. Moya-Sola described the deposit outside Barcelona as a potentially rich source of fossils from the period when great apes evolved from their common ancestors.

How this happened is still a subject of great controversy. Despite the new fossil, Moya-Sola said he was confident that the species originated in Africa, "a primate factory." Scientists "simply must find the fossils there."

Others are not so sure. The University of Toronto's David Begun said the new fossil lends credence to the view that the common ancestors evolved in Europe, then migrated back to Africa where they evolved into the African great apes and humans.

This belief, of which Begun is a leading exponent, is not shared by everyone, "to put it mildly," Begun said in a telephone interview. "But it's the most obvious conclusion," he said, and explains why there are few primate remains in Africa during the period when great apes evolved.

An assembly of the complete bones and large bone fragments of Pierolapithecus catalunicus.A reconstruction suggests what Pierolapithecus catalaunicus would have looked like. The creature lived in Spain 13 million years ago.