Stone tools existed 800,000 years earlier than thought

Marks on two 3.4 million-year-old animal bones found at an Ethiopian site were not caused by trampling but by tools made of stone, a new analysis has found.

The finding at Dikika town in Ethiopia is significant as it potentially pushes back evidence for the use of stone tools, as well as the butchering of large animals, by about 800,000 years.

Until recently, the earliest known stone tools were 2.6 million years old.

"Our analysis clearly shows that the marks on these bones are not characteristic of trampling," said study's lead author Jessica Thompson from Emory University, US.

"The best match we have for the marks, using currently available data, would still be butchery with stone tools," she said.

The 12 marks on the two specimens -- a long bone from a creature the size of an antelope and a rib bone from an animal around the size of a buffalo -- most closely resemble a combination of purposeful cutting and percussion marks, Thompson said.

"When these bones were hit, they were hit with enormous force and multiple times," she said.

The paper supports the original interpretation -- published in Nature in 2010 -- that the damage to the two bones is characteristic of stone tool butchery.

The Nature paper was followed in 2011 by a rebuttal in the Proceedings of the National Academy of Sciences (PNAS), suggesting that the bones were marked by incidental trampling in abrasive sediments.

It sparked a series of debates about the significance of the discovery and whether the bones had been trampled.

For the current paper, Thompson and her co-authors examined the surfaces of a sample of more than 4,000 other bones from the same deposits.

"One of the most important questions in human evolution is when did we start eating meat, since meat is considered a likely explanation for how we fed the evolution of our big brains," Thompson said.

Evidence shows that our genus, Homo, emerged around 2.8 million years ago.

The animal bones in the Dikika site, however, have been reliably dated to long before Homo emerged.

The study is published in the Journal of Human Evolution.