In the rain forest of the Ivory Coast 4,300 years ago, chimpanzees gathered in groups and cracked nuts the best they could, the Stone Age way. Place the nut on a hard, flat rock. Take a heavy hammer rock, and pound the nut. The chimps must have feasted well and often there under the trees by a black-water river.
Archaeologists digging in Tai National Park in Ivory Coast reported Monday the discovery of several sites where such nut-cracking chimps long ago left broken and discarded stones that were used as natural tools. Starch residues from nuts were lodged in crevices of the stones.
Very neat. Read the whole thing for their methods of identification. Don't know how strong their contention is that they didn't learn from humans who were apparently in the area at the time.