South African find gets younger

The partial skeleton of a human ancestor previously found in South Africa dates to about 2.2 million years ago, roughly 1 million years younger than the original estimates, a new study finds.

Researchers had hoped that the australopithecine fossil would shed light on the transition to an upright stance and tool use between 4 million and 3 million years ago. However, the ancient skeleton is too young to address those issues, say geologist Joanne Walker of the University of Leeds in England and her coworkers.

Their findings appear in the Dec. 8 Science.

In 1995, another investigator noticed foot bones of the australopithecine in a box holding various fossils recovered in the 1970s at Sterkfontein cave, just north of Johannesburg. After nicknaming the find Little Foot, scientists found additional bones from the same individual in other boxes and in further excavations.

Walker’s group dated Sterkfontein mineral deposits situated just above and below the fossil remains. They used a method that considered the accumulation of a specific form of lead from the radioactive decay of uranium. This technique is more accurate than the methods used in initial estimates of Little Foot’s age, the researchers hold.