A publication of the Archaeological Institute of America
A new species of human ancestor and the earliest traces of animal butchery have been discovered in the Middle Awash area of Ethiopia's Afar Desert. Dated to 2.5 million years ago the finds, which include the remains of as many as eight hominids and a selection of antelope bones butchered with the world's earliest known stone tools, were recovered from eroding sediments laid down alongside an ancient freshwater lake near the village of Bouri, which means "dust" in the Afar language, by a team lead by J. Desmond Clark and Tim D. White of the University of California, Berkeley,.
In 1996, White found the first fossils, arm and leg bones of a small hominid, eroding from a low hill. Excavation at this location revealed more pieces of a poorly preserved partial skeleton, as well as antelope bone fragments bearing the tell-tale marks left by stone implements. The individual is estimated to have stood less than 1.45 meters (four feet, nine inches) tall when alive. Moreover, the new discoveries show that the thigh bone (femur) had elongated by 2.5 million years ago, a million years before the forearm shortened, to create our familiar human proportions.
White and his team, however, are uncertain whether this hominid was the tool-user, or even what species the limb bones represent, since no teeth have been recovered from this individual. However, some 275 meters away erosion of the same geological layer exposed the skullcap of another hominid found by University of California, Berkeley, graduate student Yohannes Haile-Selassie in 1997.
The cranium had broken into many pieces which were scattered down the steep, rocky hillside. Because of the dense carbonate encrustation covering the bones, recovery and cleaning took months. The team screened the loose surface material and hauled tens of thousands of pebbles, stones and fossils to the nearby Awash River for cleaning. This was necessary to spot bone fragments within the sediments. When the left half of the upper jaw was recovered, only the tops of the teeth peeked out from beneath the encasing crust. When put together at the Paleoanthropology Laboratory in Addis Ababa, the upper jaw, or palate, was virtually complete.
According to Ethiopian anthropologist Berhane Asfaw and colleagues from the United States and Japan, who carefully examined the specimen, it demonstrates a combination of bony and dental features completely unanticipated, leading them to give it a new name, Australopithecus garhi. The word "garhi" means "surprise" in the Afar language.
Fragments of six additional individuals were found among the thousands of animal fossils from the 2.5-million-year-old sediments. Like the limb bones, the remains, which include bits of an arm, jaw, skullcap, and teeth may also belong to A. garhi.
"The new species is most like its ancestor A. afarensis, to which the well-known Lucy belongs" said White. "The face projects forward, the braincase is crested and small, but the premolars and molars are enormous. This combination of features has never been seen before, and that's why we named a new species." Its teeth are larger than A. afarensis. Its braincase, face and palate are more primitive than Homo. It lacks the specialized cranial characteristics of the robust ape-men of eastern and southern Africa. A. afarensis dates to 2.9 to 3.3 million years ago.
Antelope fossils found on the surface and in excavations show crisp, curvilinear cutmarks that could only have been made by stone tools. Some of the antelope limb bones show evidence of having been bashed open by hammerstones. These telltale traces show that by 2.5 million years ago hominids were exploiting food resources unavailable to any other primate. Methods of acquiring large quantities of high quality dietary resources (meat and marrow fat) were important because they would greatly improve our ancestors' ability to provide for themselves and their offspring. "The development of stone tool technology allowed this dietary revolution," said White. "This is the earliest evidence of a key adaptation that let our ancestors spread beyond Africa."
"We cannot yet conclusively link the new species with the butchery or the more modern limb proportions," White said. "However, the proximity of cutmarked antelope bones provides circumstantial support for this idea. Only further study will elucidate their relationship."
Prior to these discoveries, the 1.8 million-year-old Homo habilis, found by Louis S.B. Leakey and colleagues at Olduvai Gorge, Tanzania, in the early 1960s, was widely recognized as the first stone tool maker.
The relationship between the earlier ape-men, particularly A. africanus, and their stone-tool-wielding early Homo descendants have been impossible to decipher because of a gap in the East African fossil record between 2 million and 3 million years ago. The new Ethiopian fossils will help fill this void.
The discoveries come on the heels of a 1992 find by the same research team of the 4.4 million-year-old Ardipithecus, the earliest known hominid, at the nearby site of Aramis. "With the publication of these new results, and with a record spanning five million years," says White, "Ethiopia's Middle Awash has become the world's most important single site for studying human origins and evolution."
The new fossils were dated by the argon-argon radioisotopic method at the Berkeley Geochronology Center. White and his colleagues announced their findings in the April 23 edition of the journal Science. For more information on this find and the latest in paleoanthropology, look for our special anniversary section celebrating a half-century of research in the July/August 1999 issue.