A nearly complete skeleton, including skull, of what may be a 3.5-million-year-old human ancestor has been discovered in a South African cave. The bones, described at a press conference yesterday in Johannesburg, are the most complete set of hominid remains that are this old. Believed to be an early Australopithecus, the skeleton predates Lucy, the 3-million-year-old Australopithecus afarensis found in Ethiopia in 1974, and is almost as old as the 3.7-million-year-old footprints found by Mary Leakey in Laetoli, Tanzania. The discoverers say it will take another year to complete excavating the find and establish where it belongs on the human family tree.
The tale of discovery makes for a pulse-racing detective story. Ron Clarke, a paleoanthropologist at the University of the Witwatersrand Medical School in Johannesburg, says he found the first clues to the skeleton in 1994, when he identified some hominid foot bones among a pile of fossil animal remains excavated from the Sterkfontein caves near Johannesburg (Science, 28 July 1995, p. 521). Then last year, he found--in storage at the university--some lower leg bone fragments that fit with the foot bones. Convinced that the rest of the skeleton lay in the cave, he assigned two assistants to go on a "needle in a haystack" search in a large, damp, dark area called Silberberg Grotto. In just 2 days they located a piece of leg bone that exactly fit a fragment found earlier. The team eventually uncovered more bones and a skull with teeth and jawbone that is still being excavated.
Clarke is withholding judgment on just where this fossil fits in the human picture. He says the foot bones have apelike and human features, suggesting the individual was comfortable climbing trees and walking upright. With "massive" cheekbone and evidence for large jaw muscles, the skull doesn't appear to match known examples of the "gracile" variety of Australopithecus known as A. africanus. "Nonetheless, it does appear to be a form of Australopithecus," Clarke writes in the current (October) issue of the South African Journal of Science.
The find is "extraordinarily significant," says Bill Kimbel, science director of the Institute of Human Origins at Arizona State University in Phoenix. "What a wonderful thing to get complete fossils--it's what we all would love to find," adds Alan Walker of Pennsylvania State University in University Park. Walker points out that the skeleton can be used to address a host of questions relating to limb proportions, the relationship of brain size to body size, locomotion, and lifestyle. Hitherto, such relationships have been based only on fragments from different individuals.