NEW YORK – Two ancient animal bones from Ethiopia show signs of butchering by human ancestors, moving back the earliest evidence for the use of stone tools by about 800,000 years, researchers say.

The bones appear to have been cut and smashed some 3.4 million years ago, the first evidence of stone tool use by Australopithecus afarensis, the species best known for the fossil dubbed “Lucy,” says researcher Zeresenay Alemseged.

“We are putting stone tools in their hands,” said Alemseged of the California Academy of Sciences, who reports the finding with colleagues in today’s issue of the journal Nature.

Some experts urged caution about the study’s conclusions.

No stone tools were found at the site.