American anthropologists have concluded that a piece of fossil jaw found seven years ago by Burmese researchers represents the common ancestor of anthropoids, a group comprising monkeys, apes and humans.

The extinct animal, which lived between 40 million and 44 million years ago in what is now Burma, was known from a specimen discovered in the 1920s and described then as an early anthropoid. Scientists said the new find, which includes two molar teeth, confirms that the animal was an anthropoid and adds the date, which is earlier than that of any other known anthropoid.

"If we're right, this is the granddaddy of us all," said Russell L. Ciochon, an anthropologist currently at the State University of New York at Stony Brook. He reported the new interpretation in the current issue of the journal Science.

It is generally accepted that anthropoids evolved from a primate represented today by tarsiers and lemurs. These animals, called prosimians, gave rise to monkeys, which produced a lineage that became the apes. Humans evolved from the early apes.

Prosimian jawbones are thin and shallow; those of anthropoids are comparatively thick and deep. The Burmese specimen fits the anthropoid pattern.

Ciochon said the Burmese anthropoid did not look like any living species. It probably weighed 15 to 20 pounds, climbed trees and ate fruit. Its discoverer in the 1920s named it Amphipithecus mogaungensis. Amphi is Greek for "on both sides" and pithecus is Greek for ape, technically a misnomer. The second name refers to the geologic formation in which the fossils were found.

Until now, the oldest generally accepted anthropoid was a small, monkey-like creature called Aegyptopithecus, whose 35-million-year-old skeletons found in Egypt are well known. Because the Burmese specimen is older. Ciochon concludes that it was ancestral to the African species.

Ciochon, who specializes in the evolution of early anthropoids, holds that anthropoids arose in Asia and spread into Africa, giving rise to apes and humans there, and spread to the New World across an Atlantic Ocean that then was much narrower, establishing the monkeys of South America.