The team conducted their studies on the two most complete A. sediba individuals recovered thus far, an adult female and a subadult male found at a site just outside Johannesburg. Analyses of the wear on their molars showed that the two hominins ate hard foods shortly before they died. And their tooth chemistry—specifically the carbon ratios—revealed that, over their lifetime, they dined mostly on so-called C3 foods, which include trees, shrubs, some herbs and the animals that eat those kinds of plants. This is surprising, because other hominins of similar antiquity relied more heavily on C4 foods—most tropical grasses and sedges and the animals that eat those plants. Furthermore, paleoenvironmental evidence from the site that yielded the fossils attests to a setting dominated by C4 plants, not C3 ones. Among early hominins only the much older Ardipithecus ramidus from Ethiopia comes close to A. sediba’s carbon isotope composition; compared to the tooth chemistry of modern creatures, A. sediba’s looks like a savanna chimpanzee’s or a giraffe’s.
Even more startling, when the researchers examined the tartar, they found traces of plant foods no one thought our ancient kin ate, such as bark. The tartar contained silica crystals called phytoliths that plants make as a means of self-defense, some of which the investigators could attribute to particular kinds of plants on the basis of their distinctive shapes.
Scientists speculate that bark-eating may not have been their first choice. The diet and the fact that they lived in a cave may mean that they lived during a drought or stressful environmental change. Link -via Ed Yong
(Image credit: Lee Berger)