Apparently humans left behind a diet of only things picked from trees and shrubs, turning to the broader possibilities of a grass-based diet 400,000 years sooner than scientists previously thought. According to a recent John Hopkins University study, fossil evidence provides a clearer picture of our ancestors' dietary changes as they started walking on two feet.

 "A refined sense for when the dietary changes took place among early humans, in relation to changes in our ability to be bipedal and terrestrial, will help us understand our evolutionary story," Naomi E. Levin, lead author and an assistant professor in the Department of Earth and Planetary Sciences, said in a news release.

Humans started walking on the ground and in a bipedal way during the Pliocene era, which is 2.6 million to 5.3 million years ago, the release noted. Becoming more mobile and eating a grass-based diet would mean that our ancestors could have adapted their diet to eating not only grasses and roots, but the insects and animals that ate the grass as well.

According to Levin, this would have improved the species survival rate. "You can then range wider," Levin explained, "You can be in more places, more resilient to habitat change."

The researchers examined 152 fossil teeth from a wide variety of grazing species. The fossils were collected from a 100-square mile area of what is now the Afar region of Ethiopia. Among these fossils were hominin teeth. Carbon isotope distributions were used to determine what foods the fossil species ate. From this, the researchers found that both human ancestors and an extinct species of baboons ate grass-based foods as early as 3.76 million years ago. Previously, it was thought that humans adapted to this diet only about 3.4 million years ago.

"Timing is critical to understanding the context for this dietary expansion among early humans in relationship to what's happening in global climate, in vegetation communities in Africa, among other mammals, and in terms of the other evolutionary changes that are happening among early humans," Levin said in a statement. "If we know the timing of events we can start to relate them to one another."

Their findings were recently published in Proceedings of the National Academy of Sciences. 

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).