New findings state that our ancestors' diet changed and began including grasses and animals about 3.5 million years ago.

A new analysis of the teeth of our human ancestors shows that they changed their diet and started including grasses and animals in their food about 3.5 million years ago.

Prior to that, they consumed a diet similar to that of modern gorillas and chimps.

Fossilized tooth enamels of 11 species of hominines and other primates found in East Africa were analyzed for the research. It was earlier believed that they lived in forests and ate fruits and leaves from trees. However, scientists have found that this diet changed in the species Australopithecus afarensis and Kenyanthropus platyops 3.5 million years ago.

Researchers looked at samples from 175 hominins of 11 species, ranging from 1.4 to 4.1 million years old. Researchers determined their diet by studying the chemical composition of their teeth and identifying carbon isotopes within them. Different plants and animals are known to have varying levels of carbon and some of these plants were found in their teeth.

"What we have is chemical information on what our ancestors ate, which in simpler terms is like a piece of food item stuck between their teeth and preserved for millions of years," said Dr Zeresenay Alemseged, from the California Academy of Sciences, co-author on two of the papers. "Because feeding is the most important factor determining an organism's physiology, behaviour and its interaction with the environment, these finds will give us new insight into the evolutionary mechanisms that shaped our evolution."

"It is not yet clear whether the change in diet included animals, but the possible diets of some of our hominin kin" has been considerably narrowed down," Dr Matt Sponheimer, lead author of another of the papers, told BBC News.