Scientists already knew that the hunter-gatherer Kiffian occupied the region during a temperate phase. Between 6200 and 5200 B.C., one of the most severe climatic fluxes in that period's history desiccated the land and forced people out, the authors say. Soon afterward a second group arrived, the Tenerian.
But evidence of such population shifts rested largely on tool artifacts, with few human skeletons to analyze—until now. Radiocarbon dating of the bones has provided an "outstanding record" of the ancient Saharans, Sereno said.
"We have the Green Sahara written in those sand dunes, and the people who lived in it," he added.
The team discovered that the older group, the Kiffian, were buried with harpoon points and bone fishhooks, along with 6-foot (1.8-meter) Nile perch skeletons.
The presence of the fish bones and tools suggested the lake water was deeper around 7000 B.C., though probably no more than ten feet deep (three meters), Sereno said. The bones of catfish and tilapia in Tenerian burials suggest the lake was shallower later in the Holocene.
A ridge on a male Kiffian thighbone also told bioarchaeologist Chris Stojanowski of Arizona State University that the people—who ranged from six feet two inches (185 centimeters) to six feet eight inches (203 centimeters) tall—had huge leg muscles, likely from a high-protein diet and strenuous lifestyle.
The Tenerian thighbone, on the other hand, had a smaller ridge, indicating a smaller build. To adapt to an arid climate, Tenerians had a more diverse palate, including clams, fish, and savanna animals, the study says.
Stefan Krõpelin, of the Institute of Prehistoric Archaeology at the University of Cologne, finds the site impressive.
But he points out that it is a single location situated in a unique landscape at the foot of the Aïr Mountains, and shouldn't be linked to broader ancient climatic changes in the Sahara.
"Reasons behind an interruption in local human occupation of the region may have been related to a variety of socioeconomic or cultural changes, and not necessarily to general climatic deterioration throughout the Sahara," he said.
Krõpelin doubts there will be much support for the theory of a thousand-year break in rainfall throughout the entire Sahara around 6200 to 5200 B.C.
But Sereno said that the general climate record, bolstered by lake-core samples and solid animal and pollen evidence, points to this "arid interruption" period that separates the Kiffian and Tenerian.
The new study appears today in the journal PLoS One.
Stone Age Embrace
Grave goods, such as bones or tusks from wild animals—including warthogs, crocodiles, and hippos, many of which roam southern Africa today—ceramics, and ivory and shell ornaments were also found, shedding light on funerary rituals.
Perhaps most incredible was the 2006 discovery the Stone Age Embrace—a Tenerian woman facing the remains of two young children, their arms posed and hands interlaced. Pollen remnants from underneath the skeletons shows the dead had been laid on a bed of flowers. "This is a landmark burial—there's nothing like it in prehistory," Sereno said.
Though the site has provided a wealth of insights into the little-studied cultures, mysteries still persist, Sereno says.
Most puzzling is how the Tenerian dug new graves alongside the Kiffian dead without disturbing them—an "absolutely remarkable" feat, Sereno said.
The graves were also, for the most part, not clustered according to tribe—suggesting that the graves may have been marked, Arizona State's Stojanowski said.
But it's obvious why the two cultures likely buried their dead at Gobero: It was the "Daytona Beach of the Holocene," Sereno said.
"It was a strip of obviously desirable real estate that stuck out into the lake," he said—an ideal place to spot fish and incoming animals.
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