Ancient Bones 'Butchered' By Our Ancestors 2.5 Million Years Ago May Just Have Been Gnawed By Crocodiles

These are linear marks and pits on a 2.5 million-year-old ungulate leg bone from Bouri, Ethiopia. PNAS

There are stories in bones. Fossil bones covered in cuts and scrapes were thought to show proof that early humans used tools to get the meat off—demonstrating a historically game-changing timeline of tool use.

However, a new study suggests that the marks on bones may not always be made by intelligent hominids at all. They may simply be the result of crocodiles and other animals gnawing and trampling them. The study was published in the Proceedings of the National Academy of Sciences.

Over the course early-hominid anthropology, researchers have gathered hundreds of fossilized bones and analyzed the patterns on them. The bones had clearly been scraped up and damaged. They came from a variety of animals, including equids (in the horse family), bovids (in the cattle, goat, and antelope family), and even Australopithecus (in the human family). The bones were millions of years old.

If early hominids had used tools on these bones, it would represent an important milestone in the development of their intelligence. (It would also suggest cannibalism, as some of the bones were from Australopithecus.) In 2010, a paper published in Nature called marked bones in an area where Australopithecus afarensis lived the "first evidence of tool use." If true, that would put hominid tool creation, at least for cutting and scraping meat off of bones, at at least 3.4 million years old.

However, the authors of the new study say the existence of simple marking does not prove that Australopithecus should take credit for butchering and consuming all the animals whose bones were discovered.

In fact, there are a variety of things that can mark bones, outside of people with stone tools. The remains could simply have been trampled, or gnawed on by predators.

For comparison to the ancient bones, the study cited research on modern animal bones that had been trampled or fed to crocodiles. They discovered that the marks on modern bones, in controlled trampling-or-gnawing settings, were similar to the ancient marks.

In one case, the authors cite bones with marks on them that were interpreted to have been caused by early tool-makers. However, no early tools had been found in that area—only crocodile remains. They concede, though, that certain marks on certain bones are likely to have come from humans.

Bones can be damaged from erosion, the sun, plant activity, scavenging, gnawing by predators, chewing by rodents, animals stepping on them, and tool use. Without having been there, it can be difficult to unravel the mystery of what actually happened to them.