Find may support human-ape link

3.5 million-year-old skeleton found in South Africa offers clues about evolution.

Within the dank confines of a South African cave, scientists have discovered the virtually complete fossil remains of what could be one of humanity's earliest ancestors.

Dubbed "Little Foot," the 3.5 million-year-old fossil is expected to give new insights into the physical traits and capabilities of a species of early hominid.

"Exactly how much will be revealed by the skeleton will not emerge for about a year," says Ron Clarke, the University of Witwatersrand anthropologist who led the team making the discovery. "But what we do know is that it will reveal a very great deal about the anatomy and evolution of this early ape-man."

Until now, anthropologists have had to rely on fragmentary evidence - partial skulls and partial skeletons, never from the same individual - in their attempt to learn if the species, known as Australopithecus africanus, falls in the line of human evolution.

As a result, "we know enough to be controversial," says Rick Potts, director of the human origins program at the Smithsonian Institution in Washington. In the past few years, he explains, enough bone fragments have been discovered to suggest that A. africanus's build was "an intriguing amalgam of human and ape-like traits."

Now, he says, anthropologists will have a chance to test their notions on a complete specimen. Indeed, he adds, the specimen could prove to be a different species altogether. The South African research team notes that Little Foot's skull has features that appear only on another early hominid, Australopithecus robustus. But this species wasn't known in South Africa until about 1.8 million years ago. "This could be something new, adding a really interesting hominid deep down on humanity's family tree," Dr. Potts says

THE discovery involved some instinctual detective work as well as the usual chiseling. It began four years ago, when Dr. Clarke found the bones of what was to become Little Foot in the Sterkfontein caves near Johannesburg. The caves have been a fossil trove over the years.

At the time, Clarke's discovery generated excitement because it confirmed that A. africanus was a mix of human and ape-like features. The foot bones also suggested a transition between a four- and two-legged gait.

The discovery also encouraged him to search for a whole individual, because in addition to both feet, he had uncovered pieces of the lower leg bones the feet came from. He gave two assistants, Nkwane Molefe and Stephen Motsumi, plaster casts of shinbone fragments and set them to chiseling at the rock in search of the rest. Within two days, they found another piece of bone that fit their sample perfectly, leading them to uncover more of the lower leg and a complete forearm bone. Then came months of nothing. Only after chiseling in new directions, did the two find the individual, which had slumped face down, its head resting on its left arm.

"This is the most significant find to come out of Sterkfontein," says Phillip Tobias, professor emeritus of the university's anatomical sciences department. The discovery was published in yesterday's issue of the South African Journal of Science.

Once the entire fossil is excavated, determining the brain size relative to the body will help determine if the specimen is a direct ancestor of humans, says Potts.

Researchers also will be able to more clearly explain how these creatures moved. These creatures combined tree climbing and walking in ways not seen today, Potts says. "There are interesting questions about why and how this occurred. It may tell us something about the environment, that there was a lot of flux between lots of trees and few trees that required versatility."