We have a relatively good understanding of what ancient humans ate. But what did ancient Neanderthals eat? And how did that affect their survival? Scientists may have gained new insights into the Neanderthals' diet by looking at the isotope composition in the collagen from prehistoric bones.

In this latest study, the researchers examined two excavation sites in Belgium. They examined bones that were between 450,000 and 40,000 years old that belonged to mammoths, woolly rhinoceroses, wild horses, reindeer, European bison, cave hyenas, bears, lions, wolves and also Neanderthals. By looking at the collagen in the bones, the researchers found that the diet of Neanderthals differed from other predatory animals.

"Previously, it was assumed that the Neanderthals utilized the same food sources as their animal neighbors," said Herve Bocherens, one of the researchers. "However, our results show that all predators occupy a very specific niche, preferring smaller prey as a rule, such as reindeer, wild horses or steppe bison, while the Neanderthals primarily specialized on the large plant-eaters such as mammoths and woolly rhinoceroses."

Collagen is an essential organic component that is part of the connective tissue in bones, teeth, cartilage, tendons, ligaments and even the skin.

So what did Neanderthals eat? The researchers looked at the isotope composition of individual amino acids in the collagen to find out. In the end, the researchers discovered that 20 percent of a Neanderthal's diet was reliant on plant matter. This could have included berries, roots or other edible plant material. This, in particular, solves a question that has been debated for decades: whether Neanderthals were solely meat-eaters.

"In this study we were able for the first time to quantitatively determine the proportion of vegetarian food in the diet of the late Neanderthals," Bocherens said. "Similar results were found for more recent Stone Age humans."

The findings could lead to a clearer understanding of what caused the Neanderthals to go extinct 40,000 years ago. More specifically, it shows that diet was likely not the decisive factor in why they disappeared from the face of the planet at that time.

The findings are published in the journal Quaternary International.