Ancient hominid had an unusual diet

Tuesday, November 13th 2012. | Science News

Grass and sedge eating goes back at least 3 million years

By Bruce Bower

Web edition: November 12, 2012

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Grass jaw

Chemical analysis of three teeth from this fossil jaw indicates that a hominid species based in Central Africa more than 3 million years ago ate a lot of grasses and sedges.

Credit: J. Lee-Thorpe

A mysterious, 3-million-year-old member of the human evolutionary family had a maverick taste for grasses and flowering plants called sedges, a chemical analysis of the creature’s teeth suggests.

Central Africa’s Australopithecus bahrelghazali was apparently not a devotee of leaves, fruit and other standard fare of early hominids based in forested areas. Instead, it fed mainly on underground parts of grasses and sedges growing in a savanna landscape, say archaeologist Julia Lee-Thorp of the University of Oxford, England, and her colleagues. The work appears online November 12 in the Proceedings of the National Academy of Sciences.

The findings are at least 1 million years older than grass and sedge eating previously reported for another hominid, Paranthropus boisei (SN: 6/4/11, p. 8). Australopithecines such as A. bahrelghazali may have been able to eat foods available in both savanna and wooded settings, the researchers suggest. It’s also possible that the Central African species had begun to evolve an exclusive taste for grasses and sedges.

Study coauthor Michel Brunet of the University of Poitiers, France, unearthed the only known remains of A. bahrelghazali — a partial lower jaw holding seven teeth — in 1993 at Koro Toro, Chad. Based on dating of fossil-bearing soil and types of animal remains found in that sediment, researchers concluded the hominid lived between 3.6 and 3 million years ago. Some scientists assign the jaw to Australopithecus afarensis, a species that lived in East Africa more than 3 million years ago and is known for Lucy’s partial skeleton.

Chemical analyses of teeth from Lucy’s kind for dietary clues have yet to be conducted.

Australopithecus somehow made a living on the grassy savanna of Chad,” says anthropologist Stanley Ambrose of the University of Illinois at Urbana–Champaign. “Whether it ate a lot of grass or the meat of grazing animals cannot easily be determined from this chemical analysis.”

Lee-Thorp’s team measured two forms of carbon in three A. bahrelghazali teeth and in fossil teeth of various animals unearthed at Koro Toro. One form of carbon comes mostly from grasses and sedges, and the other mainly from shrubs and trees. Results showed that the hominid ate about as much grass and sedge as P. boisei did.

A. bahrelghazali probably consumed underground tubers, bulbs and stems, as well as above-ground stems of sedges such as papyrus, Lee-Thorp proposes. Primates generally have trouble digesting grass blades, she says.

Although more fossil teeth are needed to flesh out A. bahrelghazali’s eating habits, it appears that grass and sedge consumption was not limited to P. boisei, says anthropologist Peter Ungar of the University of Arkansas in Fayetteville.

“The puzzle of early hominid food choices looks more and more complicated as we add pieces to it,” Ungar says.

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