The two skulls were collected from the same layer and excavation pit as a hominid jawbone that was found at the site in 1991 and whose species identity was debated. "It was a very nice surprise to find these skulls," says co-author David Lordkipanidze of the Republic of Georgia State Museum, who notes that the well-preserved crania provided enough diagnostic detail for the researchers to compare them with other fossil human species. Their analysis showed that the Dmanisi fossils shared extensive similarities with the African species Homo ergaster from the well-known site of Koobi Fora in Kenya.
The research team discovered that the Dmanisi and Koobi Fora fossils overlap in age as well. Dmanisi contains a jackpot of chronological clues, from the isotope dates on the layer of basalt rock running beneath the site, to the paleomagnetic signature and contemporaneous animal fossils in overlying deposits.
Isotope analysis of the basalt places the age of the site at around 1.77 million years old, but the paleomagnetic signature of the sediment burrows themselves encompasses a period from 1.77 million to a little over a million years ago. Since the European faunal record is already well dated, the associated animal fossils at Dmanisi became "essential for understanding the timing of the site. Small rodents known to have lived more than 1.7 million years ago occur with the hominids," says co-author Carl C. Swisher III of the Berkeley Geochronology Center. In this case, the faunal evidence tipped the scales in favor of an earlier date.
More than 1000 stone artifacts have been recovered from the Dmanisi fossil layers, providing further support to the 1.7 million year-old date for the site. Despite the ready availability of raw material suitable for making Acheulean tools, the authors say, all of the Dmanisi artifacts are of a pre-Acheulean typ
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Contact: Ginger Pinholster
gpinhols@aaas.org
202-326-6421
American Association for the Advancement of Science
11-May-2000