Some of the oldest fossils in the human evolutionary family–including the skull and upper-arm bone shown at right–come from South Africa, according to a study in the April 25 Science.
A mix of new and already excavated Australopithecus fossils, found in two caves, date to 4 million years ago, reports a team led by Timothy C. Partridge of University of the Witwatersrand in Johannesburg. That's as many as 1 million years earlier than previous estimates for South Africa.
The scientists suspect that the bones represent two forms of Australopithecus. An Australopithecus species of comparable age lived in eastern Africa (SN: 5/16/98, p. 315).
The age estimates of the South African fossils hinged on measurements of the decay of radioactive isotopes in cave sediments.