A New Human Ancestor?

Scientists have unearthed fossils of a small-brained hominid that may be a missing link in the evolutionary tree leading to humans. The find--a 2.5-million-year-old skull--is reported in tomorrow's Science, together with two separate discoveries of the same age: hominid arm and leg bones, and animal bones showing that early hominids butchered antelopes and horses.

The new species, named Australopithecus garhi, was found in Eastern Ethiopia (garhi means "surprise" in the language of the local Afar people) by a team co-led by paleoanthropologist Tim White of the University of California, Berkeley, and several other scientists. It may fill the huge gap that still exists between the apelike creatures that lived in Africa over 3 million years ago, such as Australopithecus afarensis, best known for the famed "Lucy" skeleton, and the more humanlike members of the Homo genus which appeared just over 2 million years ago.

The most dramatic find came in 1997, when a team member spotted fragments of a skull on a slope near the village of Bouri. Digging through tons of material, the researchers found many more fragments, and they reconstructed a skull that looks unlike any other hominid species. The face is apelike in the lower part, with a protruding jaw resembling that of A. afarensis, but the teeth are unusually large, and the shape of the premolar and other dental traits are reminiscent of early Homo specimens. In the same area, the researchers also found hominid leg and arm bones, which like the skull are radiometrically dated to 2.5 million years ago. The leg bone is relatively long, like that of modern humans, but the forearm is long too, like in apes and other australopithecines.

The third find preserves evidence of hominid behavior: bones of antelopes, horses, and other animals bearing cut marks, suggesting that butchery may be the oldest human profession. One antelope bone records a sequence of failed hammerstone blows, which scratched the bone slightly and caused bone flakes to fly off. Both ends of the bone were broken off, presumably to get at the marrow. Marrow is rich in fat, and anthropologists have theorized that such a dietary breakthrough allowed the dramatic increase in brain size that took place in the Homo lineage by 2 million years ago.

The finds suggest that A. garhi may be just what paleoanthropologists were waiting for, but many are skeptical, especially because researchers can't be sure that the discoveries all represent the same hominid. There were many australopithecine species alive at this time, and A. garhi may well be an evolutionary dead end like several others, cautions paleoanthropologist Bernard Wood of George Washington University in Washington, D.C. "These are magnificent fossils," says Wood, but "at this point it's impossible to tell what's ancestral to what."

Posted in Archaeology, Paleontology, Evolution