Markings On 3.4-Million-Year-Old Bones Suggest They Were Butchered, Not Trampled

[edd]

photo credit: This is a detail of the marks on a fossilized rib bone, one of the two controversial bones. Zeresenay Alemseged.

A new analysis of 3.4-million-year-old animal bones suggests that our early ancestors may have been butchering animals with stone tools 800,000 years earlier than we thought. The findings were published in the Journal of Human Evolution last week.

Several years ago, two bones were discovered in the Hadar Formation at Dikika in Ethiopia. One is a long bone from an animal about the size of a medium antelope; the other is a rib from a buffalo-sized beast. And they were covered with a dozen marks. A 2010 study interpreted the marks as damage from stone tool butchery, but according to a 2011 paper, the marks were caused by incidental trampling by various animals over the course of millennia.

“We would really like to understand what caused these marks,” Emory University’s Jessica Thompson says in a statement. “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.” Until recently, the oldest stone tools were dated to 2.6 million years, and Homo habilis the “handy man” was thought to be the first toolmaker. But studies published this year suggest that our extinct ancestors (and likely from a different genus than ours) were making stone tools some 3 million years ago.

To investigate the controversial pair further, Thompson and colleagues studied the shapes and sizes of more than 450 marks found on 4,000 other bones collected from Dikika and nearby deposits. They then compared these to trampling marks experimentally created on modern-day bones, as well as to the marks on the two bones in question.

The marks on the hotly debated two, the team conclude, most closely resemble a combination of purposeful cutting and percussion marks – and aren’t characteristic of trampling. “When these bones were hit, they were hit with enormous force and multiple times,” Thompson explains. “The best match we have for the marks, using currently available data, would still be butchery with stone tools.”

When the team examined sand grains from the fossil site, they found that these were rounded – and not the angular type, which would have produced striations on a trampled bone. Trample marks tend to be shallow and curvy; cuts made by tools are typically straight and create a narrow, V-shaped groove. While the damage found on many of the other bones at the site seems to have been inflicted by trampling, it seems that these two bones are outliers.

Edited August 29, 2015 by edd