In August, a team of scientists including Shannon McPherron of the Max Planck Institute for Evolutionary Anthropology in Leipzig, published the results of their study into cut marks on ancient mammal skeletons found while carrying out fieldwork for the Dikika Research Project in Ethiopia.

Their report concluded that human ancestors must have been using stone tools at least 3.4 million years ago - about 800,000 years earlier than previously thought.

The trouble, according to a new report published Monday in The Proceedings of the National Academy of Sciences (PNAS), is that the Dikika Research Project scientists got it all wrong.

Bone markings called into question

"Their statement that the provenience of other previously reported younger cut-marked bones is also unknown is biasing and false," said Manuel Dominguez-Rodrigo, an archaeologist at the Complutense University of Madrid in Spain and first author of the report, in an e-mail to Deutsche Welle.

Microscopic analysis and comparisons with other bones revealed that the markings were more likely caused by animals trampling across the bones, Dominguez-Rodrigo added.

The Dikika Research project scientists, an international team of paleontologists had discovered the bones of two mammals, both of which bore deep markings.

New report suggests original theory should remain

The team concluded that the markings were created when the primitive hominid Australopithecus afarensis, of which a fossilized skeleton named Lucy is the most famous example, used stone tools to cut flesh from the bones.

Until then, the oldest evidence available for both meat-eating and stone tools had dated back 2.5 million years – and Lucy, with her large molar teeth, had always been thought to be primarily vegetarian.

When the Dominguez-Rodrigo and his team examined images of the mammal bones, they found the bones bore more resemblance to bones that had undergone lab-simulated trampling than to bones that might have been cut with stone tools.

"The earliest best evidence for hominin butchery thus remains at 2.6 to 2.5 [million years]," they wrote in their report.

Dikika researchers respond

The Dikika Research Project authors have rejected the new report, saying that the Dominguez-Rodrigo-led study did not explain away the marks, and have questioned that team’s methodology.

"Manuel Dominguez-Rodrigo did not look microscopically at the bones," McPherron told Deutsche Welle.

"Instead, he looked at our photos, many of which are taken microscopically. There is a very large difference between the two. Thus, for instance, they are obliged to re-assess our description of the V-shape of some marks from our photos whereas in our original publication we had three independent analysts each look at the actual marks."

However, Dominguez-Rodrigo rejects their rebuttal, and the exchange has become a scientific tit-for-tat.

"McPherron et al argues that the marks we published from our trampling experiments are only superficially similar to the Dikika marks," he said.

"This statement is incorrect and experts in our field will appreciate that properly. We have published in more detail than McPherron et al have the macroscopic and microscopic characteristics that make both the fossils and trampling marks virtually impossible to differentiate."

Author: Sophie Tarr

Editor: Cyrus Farivar