When Paul C. Sereno went hunting dinosaur bones in the Sahara, his career took a sharp turn from paleontology to archaeology. The expedition found what has proved to be the largest known graveyard of Stone Age people who lived there when the desert was green.
The first traces of pottery, stone tools and human skeletons were discovered eight years ago at a site in the southern Sahara in Niger. After preliminary research, Sereno, a University of Chicago scientist who had previously uncovered remains of the dinosaur Nigersaurus there, organized an international team of archaeologists to investigate what had been a lakeside hunting and fishing settlement for the better part of 5,000 years, originating some 10,000 years ago.
In its first comprehensive report, published Thursday, the team described finding some 200 graves belonging to two successive populations. Some burials were accompanied by pottery and ivory ornaments. A girl was buried wearing a bracelet carved from a hippo tusk. A man was interred seated on the carapace of a turtle.
The most poignant scene was the triple burial of a petite woman lying on her side, facing two young children. The slender arms of the children reached out to the woman in an everlasting embrace. Pollen indicated that flowers had decorated the grave.
The sun-baked dunes at the site known as Gobero preserve the earliest and largest Stone Age cemetery in the Sahara, Sereno's group reported in the current issue of the online journal PLoS One. The findings, the researchers wrote, open "a new window on the funerary practices, distinctive skeletal anatomy, health and diet of early hunter-fisher-gatherers, who expanded into the Sahara when climatic conditions were favorable."
The research was also described at a news conference in Washington at the National Geographic Society, a supporter of the project.
The initial inhabitants at Gobero, the Kiffian culture, were tall hunters of wild game who also fished with harpoons carved from animal bone. Later, a more lightly built people, the Tenerians, lived there, hunting, fishing and herding cattle. An examination of their fossilized skeletons indicated that both cultures lived and ate relatively well.
Other scientists said the discovery appeared to be spectacular evidence that nothing, not even the arid expanse of the Sahara, is changeless. About 100 million years ago, this land was forested and occupied by dinosaurs and enormous crocodiles. By 50,000 years ago, people moved in and left stone tools and mounds of shells, fish bones and other refuse. The lakes dried up in the last Ice Age.
Then the rains and lakes of a fecund Sahara returned some 12,000 years ago, and remained, except for one 1,000-year interval, until about 4,500 years ago. Geologists have long known that the region's basins retained mineral residue of former lakes, and other explorers have found scatterings of human artifacts from that time, as Sereno did at Gobero in 2000.
"Everywhere you turned, there were bones belonging to animals that don't live in the desert," he said. "I realized we were in the green Sahara."
Human skeletons were eroding from the dunes, jawbones with nearly full sets of teeth and finger bones of a tiny hand pointing up from the sand. Sereno said that the skeptical reaction of archaeologists to his original reports prevented him from securing support for intensive explorations of the site until 2005 and 2006.
From an analysis of the skeletons and pottery in those two seasons, scientists identified the two successive cultures that occupied the settlement. The Kiffians, some of whom stood up to 6 feet tall, both men and women, lived there during the Sahara's wettest period, between 10,000 and 8,000 years ago. They were primarily hunter-gatherers who speared huge lake perch with harpoons.
Elena A. A. Garcea, an archaeologist at the University of Cassino in Italy, identified ceramics with wavy lines and zigzag patterns as Kiffian, a culture associated with northern Africa. Pots bearing a pointillistic pattern were linked to the Tenerians, a people named for the Teneri Desert, a stretch of the Sahara known to Tuareg nomads as a "desert within a desert."
Christopher M. Stojanowski, an archaeologist at Arizona State University, said the two cultures were "biologically distinct groups." The bones and teeth showed that in contrast to the robust Kiffians, the Tenerians were typically short and lean and apparently led less rigorous lives. Perhaps, Stojanowski said, they had developed more advanced hunting technologies for taking smaller fish and game.
The shapes of the Tenerian skulls are puzzling, researchers said, because they resemble those of Mediterranean people, not other groups from the southern Sahara.
Sereno said in an interview that both cultures, the Tenerians in particular, appeared to have settled into semi-sedentary lives in a more or less year-round community. Families, he said, are not usually part of mobile hunting parties, and yet many of the burials at the site are of juveniles. The abundant refuse mounds also attested to long-term occupation.
Asked if he had adjusted to the transition from dinosaur paleontology to Stone Age archaeology, Sereno said, "It's still weird for me to be digging up my own species."