Grass Was Quite Yummy For Early Human Ancestors
November 14, 2012

Fossil Analysis Shows That Early Hominins Preferred Tropical Grasses And Sedges

Lee Rannals for - Your Universe Online

Our ancestors about 3.5 million years ago had a diet that mainly consisted of tropical grasses and sedges, according to a new study.

Scientists reported in the Proceedings of the National Academy of Sciences (PNAS) that they extracted information from the fossilized teeth of three Australopithecus bahrelghazali individuals, which were the first early hominins excavated at two sites in Africa.

"We found evidence suggesting that early hominins, in central Africa at least, ate a diet mainly comprised of tropical grasses and sedges," said Professor Julia Lee-Thorp, a specialist in isotopic analyses of fossil tooth enamel. "No African great apes, including chimpanzees, eat this type of food despite the fact it grows in abundance in tropical and subtropical regions."

He said that the only notable exception that ate this type of food is the savannah baboon, which still forages these types of plants today.

"We were surprised to discover that early hominins appear to have consumed more than even the baboons," Lee-Thorp said.

The paper suggests this discovery demonstrates how early hominins experienced a shift in their diet relatively early. The finding is significant to show how early humans were able to survive in open landscapes with few trees.

This landscape allowed them to move out of the earliest ancestral forests or denser woodlands, and occupy and exploit new environments, according to the study.

The fossils of the individuals range between three million and 3.5 million years old, and originate from two sites in the Djurab desert.

In the paper, the authors said that at the time when Australopithecus bahrelghazali roamed around, the area would have had reeds and sedges growing around a network of shallow lakes, with floodplains and wooded grasslands.

Scientists previously thought that early human ancestors acquired tougher tooth enamel, large grinding teeth and powerful muscles so they could eat foods like hard nuts and seeds. The latest research shows that the diet of early hominins diverged from that of the standard great ape at a much earlier stage.

The authors said that it is unlikely that the hominins would have eaten the leaves of the tropical grasses because they would've been too abrasive and tough to break down and digest.  Instead, the scientists believe these early hominins may have relied on the roots, corms and bulbs at the base of the plant.

"Based on our carbon isotope data we can´t exclude the possibility that the hominins' diets may have included animals that in turn ate the tropical grasses," Lee-Thorp said. "But as neither humans nor other primates have diets rich in animal food, and of course the hominins are not equipped as carnivores are with sharp teeth, we can assume that they ate the tropical grasses and the sedges directly."