Ancient skull spurs rift over hominid ties.

Ancient skull spurs rift over hominid ties

A 9- to 10-million-year-old fossil skull unearthed last fall in Greece represents a direct ancestor of hominids -- the evolutionary family that includes modern humans -- and may even be the earliest known example of a hominid, its discoverers contend.

The controversial new specimen belongs to the species Ouranopithecus macedoniensis, previously known only from fragmentary remains. It possesses some facial features similar to those of several ancient apes considered ancestral to modern orangutans, reports a team led by Louis de Bonis of the University of Poitiers in France. But the size and shape of its teeth are closer to Australopithecus afarensis, the 3.5-million-year-old African hominid group that includes the remains of "Lucy," the French group maintains.

If Ouranopithecus is a direct forerunner of hominids, then it may have branched off from African gorillas and chimpanzees around 12 million years ago, the researchers suggest in the June 21 NATURE. In contrast, many scientists now hold that hominids diverged from African great apes between 5 million and 10 million years ago.

However, several paleoanthropologists familiar with the Greek skull doubt it is a hominid ancestor.

"I'd be extremely surprised if de Bonis' interpretation is true," says Eric Delson of the City University of New York, who has seen photographs of the Greek find. "Ouranopithecus was probably on the orangutan lineage."

Jeffrey Schwartz of the University of Pittsburgh agrees. Much of the upper face of the Ouranopithecus specimen is orangutan-like, he notes. For instance, the steeply sloped floor of the nasal cavity and the wide space between oval eye sockets clearly link the skull to orangutans, Schwartz says. Moreover, dental features shared with A. afarensis are not highly specialized and also appear in other ancient ape species not directly linked to hominids, he maintains.

Remains of several ape genera dating to between 15 million and 7 million years ago have previously been found in Africa and Asia, but neither those animals nor Ouranopithecus display clear anatomical links to hominids, writes Peter Andrews of the Natural History Museum in London, England, in a commentary accompanying the research report.

The new specimen includes much of the face, part of the skull cap and the entire upper jaw with all its teeth save for one molar. Bones of ancient cattle, giraffes and mastodons found in the same sediment as the skull resemble animal remains at nearby sites dated at 9 million to 10 million years old.

The skull came from an adult male, de Bonis' group asserts. Its canines closely resemble Ouranopithecus canines previously identified as male, they point out. But canines in the new specimen are smaller than in any recent or ancient great ape and closer in size to those of A. afarensis. Round and swollen molar cusps and a brow ridge that does not project from the face also link Ouranopithecus to early hominids, the French scientists say.

Delson argues that assigning a sex to the Greek skull is difficult, considering the fragmentary nature of most Ouranopithecus remains. Round and swollen molar cusps -- the product of extremely thick tooth enamel -- characterize a wide range of ancient apes, not just Ouranopithecus, he adds.

From about 15 million to 7 million years ago, as many as five genera on the orangutan lineage lived throughout central Europe and Asia, including Ouranopithecus, Sivapithecus in south Asia and Lufengpithecus in China, Delson contends. Gorillas, chimpanzees and hominids probably originated in Africa, he says. Their evolutionary relationship to the 14-million-year-old African ape Kenyapithecus -- known only from teeth and facial fragments -- remains unclear, he adds.