Fossilized teeth suggest that our primate ancestors began adding grass-based food to their diets about 400,000 years earlier than experts once thought.

The finding means early hominins took this important step—one of several in that approximate time period—toward becoming Homo sapiens 3.8 million years ago.

The shift in eating habits would have broadened our ancestors’ horizons and improved their species’ capacity for survival, says geologist Naomi Levin of Johns Hopkins University, who led the research.

She and colleagues describe the work online in the Proceedings of the National Academy of Sciences.

Leaving the trees

“You can then range wider,” Levin says of the hominins’ broadening of their diets to include grasses and their roots and also insects or animals that ate grass. “You can be in more places, more resilient to habitat change” and thus more likely to survive, she says.

Previously, hominin diets focused on foods from trees and shrubs. At roughly the same time as the dietary change—during the Pliocene era, 2.6 million to 5.3 million years ago—human precursors were starting to come down out of the trees and travel on two feet on the ground.

“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,” says Levin, an assistant professor of earth and planetary sciences.

fossil tooth from hominin

“This research reveals surprising insights into the interactions between morphology and behavior among Pliocene primates,” says coauthor Yohannes Haile-Selassie of the Cleveland Museum of Natural History.

“The results not only show an earlier start to grass-based food consumption among hominins and baboons but also indicate that form does not always precede function. In the earliest baboons, dietary shift toward grass occurred before its teeth were specialized for grazing.”

Human ancestors and ancient baboons

Researchers analyzed 152 fossil teeth from an array of animals including pigs, antelopes, giraffes, and human ancestors gathered from a roughly 100 square-mile area of what is now the Afar region of Ethiopia.

Among the samples were teeth from hominins—including contemporary humans and our extinct ancestors—believed to represent 16 different individuals, says Levin.

The teeth were examined for carbon isotope distribution, a marker that can distinguish the types of foods the animals ate. The data show that both human ancestors and members of a now-extinct, large species of baboon were eating large amounts of grass-based foods as early as 3.76 million years ago. Previous research dated the earliest evidence for grass-based foods in early human diets to 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 says. “If we know the timing of events we can start to relate them to one another.”

Levin and Haile-Selassie worked with Stephen R. Frost of the University of Oregon and Beverly Z. Saylor of Case Western Reserve University.


This text is published here under a Creative Commons License.
Author: Arthur Hirsch-Johns Hopkins University
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