Use of stone tools and the practice of butchering large animals for meat had begun 800,000 year earlier than believed, according to a new study of two 3.4 million-year-old animal bones found in Ethiopia.
The 12 marks on the two bones were not caused by trampling but by stone tools used by our meat eating ancestors, researchers found.
"Our analysis clearly shows that the marks on these bones are not characteristic of trampling," said lead author Jessica Thompson, an assistant professor of anthropology at Emory University in US.
"The best match we have for the marks, using currently available data, would still be butchery with stone tools," Thompson said.
The marks on the two specimens found in Dikika, Ethiopia - a long bone from a creature the size of a medium antelope and a rib bone from an animal closer in size to a buffalo - most closely resemble a combination of purposeful cutting and percussion marks, Thompson said.
The study supports the original interpretation that the damage to the two bones is characteristic of stone tool butchery, published in the journal Nature in 2010.
That finding was sensational, since it potentially pushed back evidence for the use of stone tools, as well as the butchering of large animals, by about 800,000 years, researchers said.
The Nature paper was followed in 2011 by a rebuttal in the journal PNAS, suggesting that the bones were marked by incidental trampling in abrasive sediments.
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.
They then used statistical methods to compare more than 450 marks found on those bones to experimental trampling marks and to the marks on the two controversial specimens.
Evidence shows that our genus, Homo, emerged around 2.8 million years ago. Until recently, the earliest known stone tools were 2.6 million years old.
The animal bones in the Dikika site, however, have been reliably dated to long before Homo emerged.
One way that experimental archaeologists learn to interpret marks on fossil bones is by modifying modern-day bones.
They hit bones with hammer stones, feed them to carnivores and trample them on various substrates, then study the results.
Based on knowledge from such experiments, the researchers diagnosed the marks on the two bones from Dikika as butchery in a blind test, before being told the age of the fossils or their origin.
The researchers collected a random sample of fossils from the same deposits as the controversial specimens, as well as nearby deposits.
"The marks on the two bones in question don't look like other marks common on the landscape. The marks are bigger, and they have different characteristics," Thompson said.
The study was published in The Journal of Human Evolution.
