South African fossil surprises.

An underground cavern in South Africa known as Sterkfontein yielded an important trove of hominid fossils in a series of excavations more than 35 years ago. Finds included the approximately 2.5-million-year-old bones of Australopithecus africanus, a creature whose place in human evolution remains unclear, and the remains of an early Homo species from around 1.5 million years ago.

Sterkfontein excavations conducted over the past 8 years have unearthed nearly 600 hominid fossils that may shake up current theories about our evolutionary family tree, asserts Lee R. Berger of the University of the Witwatersrand in Johannesburg, South Africa.

The most striking discovery is a partial skeleton of an A. africanus individual whose apelike body was capable of only limited two-legged walking, Berger contends. The find includes bones from the shoulder, arm, spine, and pelvis.

Anatomical analysis indicates that this hominid used powerful arms to climb in trees much of the time, Berger contends. Although the shoulder fossils are fairly thin and light, they contain grooves where large muscles were once attached. Upper and lower arm bones appear more apelike than humanlike, he adds.

The pelvis is unusually small, according to Berger. It has a generally apelike shape combined with several features of a two-legged gait already noted in A. afarensis, an East African hominid that lived from 4 million to 3 million years ago. The famous partial skeleton of Lucy belongs to A. afarensis.

New A. africanus fossils at Sterkfontein date to between 2.9 million and 2.6 million years ago and come from hominids who walked less steadily on two legs than Lucy's species, Berger concludes. This suggests that hominids in eastern and southern Africa evolved separately after splitting off from a common ancestor, with perhaps the southern branch spawning the Homo line, the South African scientist proposes.