When it came to eating, an upright, 2 million-year-old African hominid had a diet unlike virtually all other known human ancestors, says a study led by the Max Planck Institute of Evolutionary Anthropology in Leipzig, Germany and involving the University of Colorado Boulder. The study indicated that Australopithecus sediba -- a short, gangly hominid that lived in South Africa -- ate harder foods than other early hominids, targeting trees, bushes and fruits. In contrast, virtually all other ancient human ancestors tested from Africa -- including Paranthropus boisei, dubbed "Nutcracker Man" because of its massive jaws and teeth -- focused more on grasses and sedges（莎草） , said CU-Boulder doctoral student Paul Sandberg, a co-author on the new study.

The A. sediba diet was analyzed using a technique that involved zapping fossilized teeth with a laser, said Sandberg. The laser frees telltale carbon from the enamel（搪瓷，珐琅） of teeth, allowing scientists to pinpoint the types of plants that were consumed and the environments in which the hominids lived. The carbon signals from the teeth are split into two groups: C3 plants like trees, shrubs and bushes preferred by A. sediba, and C4 plants like grasses and sedges consumed by many other early hominids.

The teeth from the two A. sediba individuals analyzed in the study had carbon isotope values outside the range of all 81 previously tested hominids. "The lack of any C4 evidence, and the evidence for the consumption of hard objects, are what make the inferred diet of these individuals compelling," said Sandberg.

"It is an important finding, because diet is one of the fundamental aspects of an animal, one that drives its behavior and ecological niche. As environments change over time because of shifting climates, animals are generally forced to either move or to adapt to their new surroundings," said Sandberg of CU-Boulder's anthropology department.

The researchers concluded from their scientific tests that bark and other fracture-resistant foods were at least a seasonal part of the A. sediba diet. While bark and woody tissues had not been previously documented as a dietary component of any other ancient African hominids, such foods are consumed by many contemporary primates and contain both protein and soluble sugars. The diet of A. sediba may have been similar to that of today's African savanna（热带草原） chimpanzees, Sandberg said.

One unique aspect of the project was the analysis of microscopic, fossilized particles of plant tissue known as phytoliths trapped in ancient tooth tarter, a hardened form of dental plaque（牙菌斑） , said corresponding study author Amanda Henry of the Max Planck Institute for Evolutionary Anthropology.

"The fact that these phytoliths are preserved in the teeth of 2 million-year-old hominids is remarkable and speaks to the amazing preservation at the site," said Sandberg. "The phytolith data suggest the A. sediba individuals were avoiding the grasses growing in open grasslands that were abundant in the region at the time."

A third, independent line of study -- analyzing microscopic pits and scratches on A. sediba teeth, which reveal what they were eating at the time just prior to death -- also confirmed that at least one of the hominids was eating harder foods, said Sandberg.

A paper on the subject was published online by Nature on June 27. Other paper authors included Professor Matt Sponheimer of CU-Boulder, Peter Ungar of the University of Arkansas, Benjamin Passey of Johns Hopkins University, Lloyd Rossouw of the Bloemfontein National Museum in Bloemfontein, South Africa, Lee Berger and Marion Bamford of the University of Witwatersrand in Johannesburg, South Africa and Darryl de Ruiter of Texas A&M University.