Researchers in Barcelona, Spain, say they have uncovered a relatively complete fossil of one of the earliest great apes, the category that includes human beings. A report published today in the journal Science describes the new species, Pierolapithecus catalaunicas, which lived between 12.5 million and 13 million years ago. Apes diverged from monkeys near the beginning of the Miocene epoch about 25 million years ago. As long ago as 19 million years ago, the great apes then parted ways with the lesser apes, a group that includes modern gibbons. Dozens of species of great apes lived during the Miocene, but only humans, chimpanzees, gorillas and orangutans remain.

The fossil includes parts of a skull that has a rather vertical face as well as other bones that show features characteristic of great apes. For example, the highly curved rib bones indicate that Pierolapithecus had a broad flat chest and its shoulder blades were on its back rather than on the sides of its chest, as in monkeys. These features, together with a flexible wrist joint, are thought to help in swinging from branches. Although the specimen has short fingers similar to those of monkeys, its discoverer, Salvador Moy-Sol of the M. Crusafont Institute of Paleontology, and his colleagues propose that long fingers like those of great apes may have evolved later. Like modern great apes, Pierolapithecus's lower back was short and stiff, which is suggestive of an upright posture.

The remains date from about the time when the Asian great apes, represented today by orangutans, diverged from the African branch of great apes that later produced gorillas, chimpanzees and humans. The authors suggest that their specimen is close to the common ancestor of both branches. David Begun of the University of Toronto, a paleoanthropologist not affiliated with the new find, suspects that Pierolapithecus may actually be partway along the African branch. But he emphasizes that because this fossil came from a time so close to the divergence, the differences between the branches would be slight. Says Begun: "Either way, we still get a glimpse, through Pierolapithecus, of what the common ancestor of all great apes looked like, even if it's actually a little way along one of those two major pathways."