American Association for the Advancement
New fossils may be first human ancestors out of Africa, say Science authors
Press release, 11 MAY 2000; see article abstract below
See also BBC's coverage, with photograph.
Washington, D.C-- A nearly complete fossil cranium and another skullcap, representing the earliest known human ancestors from Eurasia, may also belong to the first hominid species to journey out of Africa. A team of Georgian, German, French and U.S. researchers describe these "First Eurasians" from the site of Dmanisi in the Republic of Georgia in the 12 May issue of Science.
The Science authors say that these 1.7 million year-old fossils are the first fossils discovered outside of Africa to show clear signs of African ancestry. The age and skeletal characteristics of the Dmanisi skulls link them to the early human species Homo ergaster, a species that some researchers believe is the African version of Homo erectus.
Most scientists think that Homo erectus was the first hominid species to leave the African continent, although the exact identity of these ancestral travelers and the timing of their departure has been hotly debated for decades. Under the classic scenario, Homo erectus, armed with an advanced tool kit called the Acheulean or hand-ax tradition, became the first human species capable of braving an array of challenging environments outside the African cradle.
The Dmanisi fossils, however, may undermine this tale of the technologically triumphant hominid. Stone tools found with the two skulls are of the less sophisticated "pebble-chopper" type that preceded the Acheulean in Africa, and the site itself is older than any known Acheulean tools. The tools, along with details of the fossils' anatomy and the age of the site, "argue for early, pre-Acheulean migrations out of Africa," say the authors.
The fossils were retrieved during the course of archaeological investigations of a medieval castle at Dmanisi. Meticulous geological investigation confirms that the human fossils, accompanying animal bones, and tools come from sediment-filled, irregularly-shaped "burrows," scooped out of the ancient strata by the flow of groundwater, according to co-author Reid Ferring of the University of North Texas.
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 type that appeared in Africa as early as 2.4 million years ago.
If superior technology didn't lead the way out of Africa, as the Dmanisi evidence suggests, what other factors may have prompted these early humans to leave the continent? The Science authors speculate that the move might have been appetite-driven. "Basically the argument that we're making is that during that time in Africa, the savanna is expanding and there is a greater availability of 'protein on the hoof'," explains co-author Susan Antón of the University of Florida in Gainesville. "With the appearance of Homo, we see bigger bodies that require more energy to run, and therefore need these higher quality sources of protein as fuel." Antón notes that as early humans shifted their diets to include larger amounts of animal protein, there probably was a corresponding expansion in their home range to match the ranges of these animals.
Along with Ferring, Lordkipanidze, Swisher, and Antón, the Dmanisi research group includes Director Leo Gabunia and Abesalom Vekua of the Republic of Georgia National Academy of Sciences, Antje Justus, Gerhard Bosinski, and Olaf Jöris of the Romisch-Germanisches Zentralmuseum, Merab Tvalchrelidze, Givi Majsuradze, Aleksander Mouskhelishvili, and Media Nioradze of the Republic of Georgia State Museum, and Marie-A. de Lumley of the Laboratoire Muséum National d'Histoire Naturelle, CNRS.
Earliest Pleistocene Hominid Cranial Remains from Dmanisi, Republic of Georgia:
Taxonomy, Geological Setting, and Age
Leo Gabunia, 1 Abesalom Vekua, 1 David Lordkipanidze, 2* Carl C. Swisher III, 3 Reid Ferring, 4 Antje Justus, 5 Medea Nioradze, 2 Merab Tvalchrelidze, 2 Susan C. Antón, 6 Gerhard Bosinski, 5 Olaf Jöris, 5 Marie-A.-de Lumley, 7 Givi Majsuradze, 2 Aleksander Mouskhelishvili 2
Science 288. 5468 (12 May 2000): 1019 - 1025
Archaeological excavations at the site of Dmanisi in the Republic of Georgia have uncovered two partial early Pleistocene hominid crania. The new fossils consist of a relatively complete cranium and a second relatively complete calvaria from the same site and stratigraphic unit that yielded a hominid mandible in 1991. In contrast with the uncertain taxonomic affinity of the mandible, the new fossils are comparable in size and morphology with Homo ergaster from Koobi Fora, Kenya. Paleontological, archaeological, geochronological, and paleomagnetic data from Dmanisi all indicate an earliest Pleistocene age of about 1.7 million years ago, supporting correlation of the new specimens with the Koobi Fora fossils. The Dmanisi fossils, in contrast with Pleistocene hominids from Western Europe and Eastern Asia, show clear African affinity and may represent the species that first migrated out of Africa.
1 Republic of Georgia National Academy of Sciences, Tbilisi, 380007, Republic
2 Department of Geology and Paleontology, Republic of Georgia State Museum,
3 Purtseladze Street, Tbilisi, 380007, Republic of Georgia.
3 Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USA.
4 Department of Geography, University of North Texas, Denton, TX 76203, USA.
5 Romisch-Germanisches Zentralmuseum, Mainz, Germany.
6 Department of Anthropology, University of Florida, Gainesville, FL 32611, USA.
7 Laboratoire Muséum National d'Histoire Naturelle, CNRS, Paris, France.
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