The genus Homo is no longer the sole primate lineage known to have used stone tools to consume the meat of large mammals. New research pushes that skill back nearly a million years.

Large fossilized animal bones with ends shattered for sucking out marrow and cut marks deliberately made with sharp stone tools have been found just a few hundred feet from a previously uncovered Australopithecus aferensis skeleton. The bones are roughly 3.4 million years old, and connect the earliest evidence for using stone tools and eating large game to our Lucy-like ancestors.

Previously, the earliest evidence for using tools to cut the meat off large animals was attributed to early Homo in the Gona region of Ethiopia around 2.5 million years ago. This find from a different region in Ethiopia, Dikika, shows the behavior was around at least a million years earlier.

'It means almost everything to be able to use stone tools," said paleontologist Zeray Alemseged of the California Academy of Sciences, co-author of the discovery announced August 12 in Nature. "The picture that we're going to paint of Australopithecus is being transformed completely. We can now imagine them walking around carrying their tools. Tools that were the precursor of every tool that we have today."

"Australopithecus was a very primitive, ape-like early human," said biological anthropologist Craig Stanford at University of Southern California, who edited a book on meat eating and human evolution. "The fact that they were using tools and eating meat indicates this was something that was widespread very early in human history."

Two parallel cutmarks made by stone tools on the rib of a cow-sized mammal Image credit: Dikika Project

The ability to carve meat off large mammal carcasses likely put Australopithecus in competition with dangerous scavengers, Alemseged says. It is unlikely they were hunting for the large game because their body shape would not have allowed them to run fast, which is necessary to chase down an antelope or similar sized animal.

But scavenging large animals still provides access to high quality, high calorie foods that likely enabled Australopithecus to venture much further out of the forest environment into the open grassland than otherwise possible on a diet of mostly of fruit, leaves and tubers.

The two cut bones found both came from mammals. One is a rib from a cow-sized animal, and the other is a femur shaft from an antelope-sized animal. Analysis of the bones showed the cut marks were created before the bones fossilized, eliminating the possibility the marks were made recently.

While it is impossible to tell from the scratches whether Australopithecus was making stone tools or using naturally sharp rocks, the lack of adequate rock material in the immediate area where the bones were found suggests they were carrying the stones around with them from one place to another.

However, no one has yet found the stone tools themselves or where they could have come from, and at least one scientist finds this reason to be skeptical of the claims made by the discoverers.

"The fact that no single sharp-edged flaked stone has been recovered from the site makes such a claim doubtful of any hominid involvement," said paleontologist Sileshi Semaw of the Stone Age Institute, who discovered what was previously the oldest evidence for stone tool from the Gona region. "Researchers who study bone surface modifications from archeological sites have shown that fresh bones trampled by animals can create marks that mimic stone tool cut marks."

"The next stage will be to really go out there and scrutinize the site to see if the tools are indeed there," said Alemseged in response. "But I wouldn't be surprised if the stone tools were archeologically invisible to us. They might have been using the tools in a sporadic way."