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Hominid 'caches' get bone-wear boost.

Hominid 'caches' get bone-wear boost

As scientists learn more about the formation of archaeological sites thought to have been used by early human ancestors, or hominids, the behavior of our ancient forebears becomes, paradoxically, less clear.

A good example is a new study by anthropologist Richard Potts of the Smithsonian Institute in Washington, D.C. After conducting the first analysis of bone weathering among animal remains at hominid sites, he reports that human ancestors transported the bones over a period of at least five to 10 years to several sites in Olduvai Gorge, Tanzania, dated at between 1.70 million and 1.85 million years old. Although hominids returned to the sites over a number of years, says Potts, investigators have no clear notion of how often meat was eaten at these spots, whether food sharing or other social activity took place and what proportion of bones were the result of hunting as opposed to scavenging.

The finding, published in the winter PALEOBIOLOGY, does support Potts's "stone-cache hypothesis," which holds that stone tools were kept at the Olduvai sites where foods were taken to be cut up or otherwise processed. The sites were frequented by various carnivores Potts, so hominids kept their visits brief. In contrast, he points out, modern hunter-gatherers typically occupy campsites or "home bases" for up to several months before moving on to another camp.

The stage was set for Potts to elaborate on the stone-cache hypothesis in 1978, when Anna K. Behrensmeyer of the Smithsonian Institution described progressive stages of decomposition due to weathering in the bones of large mammals found in East African savannas. These savannas, says Potts, are excellent mirrors of ancient conditions at Olduvai. Each stage was linked to open-air exposures of up to 15 years; by that time, bones tend to disintegrate if they are not buried. In a further test of modern remains, Potts studied 605 mammal bones from a spotted-hyena den in the same East African region. He found that small bones tend to weather more slowly because they are temporarily buried and then uncovered as hyenas trample the den floor. The weathering analysis of long bone shafts, however, provided the best picture of the gradual accumulation of bones in the den.

Thus, Potts zeroed in on long bone shafts from six Olduvai sites. Each site yielded 34 to 150 specimens. Using Behrensmeyer's stages of weathering, he found that bones at all of the Olduvai sites accumulated over at least five to 10 years, a time span similar to that observed in the modern hyena den. Among hyenas, observes Potts, the dens are mainly used as temporary feeding stations by adult foragers. Hominids, he says, may have followed a similar pattern.

Furthermore, Potts explains that Olduvai animal bones displaying all stages of weathering have previously been found to contain both the tooth marks of carnivores and the cut marks of hominid tools. "Evidently," he says, "hominids and carnivores modified bones over about the same period of time, as though over a succession of occupations or visits to each site."

This interpretation conflicts with the suggestion of anthropologist Lewis Binford that the Olduvai remains largely represent animal death sites rather than bone collections transported by hominids. Binford, of the University of New Mexico in Albuquerque, holds that hominids scrounged from carcasses abandoned by carnivores and consumed more bone marrow than meat (SN:3/9/85, p. 155).

The next step in resolving the controversy over how hominids used the Olduvai sites, says Potts, is for scientists to develop testable hypotheses to explain why the hominids kept coming back to the same spots.
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Title Annotation:research in behavior of early human ancestors
Author:Bower, Bruce
Publication:Science News
Date:Apr 26, 1986
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