Scientists have discovered in Ethiopia what may be the earliest known fossil from a member of our own genus, Homo: an upper jaw dated at about 2.33 million years old. Announced in the Ethiopian capital Addis Ababa earlier today, the find is expected to shed light on a murky period between 2 million and 3 million years ago, when three different Homo species, as well as several species of their apelike ancestors, the australopithecines, roamed Africa's grassy plains.
An international team of American, Ethiopian, and Israeli scientists, led by paleoanthropologists William H. Kimbel and Donald C. Johanson and geochronologist Robert C. Walter of the Institute of Human Origins in Berkeley, California, found the jaw in November 1994 on a barren slope at Hadar in northern Ethiopia. The site lies only 5 kilometers from where Johanson and colleagues discovered the famous fossil ``Lucy,'' the most complete skeleton of the small-brained, big-jawed Australopithecus afarensis that lived 3.0 to 3.8 million years ago. But when Kimbel fit together the two halves of the upper jaw or maxilla, he knew right away that this was no australopithecine: ``It's Homo. There's no question about it.'' For example, the new maxilla has a broad dental arch and a short, flat snout like those of younger Homo, rather than the projecting face and narrow palate of an australopithecine.
Another clue to the new fossil's identity might be an assemblage of 34 Oldowan stone tools found near the jawbone. At other sites such tools have been considered the handiwork of a primitive human species called Homo habilis, but for now the team can't rule out the idea that another species made them. And more fossils are needed before the specimen can be assigned to a particular species. Although the jaw isn't enough to determine which species of Homo came first, it may help determine which anatomical traits were inherited from an australopithecine ancestor--and which ones arose in Homo itself, says Kimbel. The discovery will be published in the December issue of the Journal of Human Evolution.
To learn more about the species represented by the new jaw, and perhaps pin down its australopithecine ancestor, the team plans to return to Hadar next fall for more fossils. Notes University of Liverpool paleoanthropologist Bernard Wood: ``The important thing about this is we've started to discover fossiliferous strata of the right sort of age. Now that they've found one hominid, my guess is they will find more specimens.''