Put that stone down, Lucy, and back away from the antelope tartare.
Marks on two fossil bones, recently presented as evidence that Lucy’s ancient hominid species butchered animals for meat, likely resulted from animal trampling, say anthropologist Manuel Dominguez-Rodrigo of Complutense University of Madrid and his colleagues.
Scientists excavating Ethiopia’s Dikika research area unearthed a pair of 3.4-million-year-old animal bones that, in their view, bear incisions created as Lucy’s kind, Australopithecus afarensis, sliced meat off carcasses with sharp stones found on the landscape (SN: 9/11/10, p. 8). That precedes what had been the earliest butchery marks on animal fossils by about 800,000 years (SN: 4/24/99, p. 262).
But the experimentally produced trampling damage on animal bones looks much like marks on the allegedly butchered fossils, Dominguez-Rodrigo’s team asserts in an upcoming Proceedings of the National Academy of Sciences.
“The interpretation that primitive creatures like Australopithecus, with chimp-sized brains, were using stone tools 3.4 million years ago and eating meat from large animals is currently unsupported,” Dominguez-Rodrigo says.
Archaeologist Curtis Marean of Arizona State University in Tempe, a coauthor of the carnivorous-Lucy paper, rejects Dominguez-Rodrigo’s argument. Some marks on experimentally trampled bones resemble those in photographs of the Dikika bones, but two deep incisions on one fossil look far more like butchery marks than like any reported trampling damage, Marean says.
In addition, Dominguez-Rodrigo initially compared trampling damage to butchery marks produced by human-made stone tools, not stones with naturally sharp edges. Lucy’s kind probably collected sharp stones rather than making them, in Marean’s view. Stones that happen to have sharp edges create butchery marks resembling much of the damage on the Dikika bones, he asserts.
Both Dikika fossils were surface finds. It’s hard to know whether they originally rested in a nearby sand bed — as argued by their discoverers — or came loose from harder sediment, Dominguez-Rodrigo says. If the fossils broke free from surrounding material, abrasive soil could have created many of the cuts and scratches attributed to stone tools, he suggests.
If the fossils lay in a sand bed, animal trampling would have produced marks indistinguishable from those cited as butchery damage, in his view.
Those conclusions rest on comparisons of damage to the Dikika bones with animal bones trampled in a 2009 study directed by Dominguez-Rodrigo. Three men of varying weights, wearing shoes with soles covered by coarse grass, walked across deer bones that had been placed in a sandy mix similar to the Dikika sand bed.
Two minutes of trampling resulted in long, thin indentations that were _/-shaped in cross-section. Animal butchery with stone tools rarely results in such bone damage, but signature trampling marks appear on the Dikika bones, Dominguez-Rodrigo says.
Incisions attributed to butchery by Marean don’t look like typical trampling marks, but cuts such as those still sometimes appear on experimentally trampled bones, Dominguez-Rodrigo adds.