sexta-feira, 29 de junho de 2012

Australopithecus sediba: The Wood-Eating Hominid

The dental plaque on Australopithecus sediba teeth reveals the species ate wood or bark.
Image courtesy of Amanda Henr
Sometimes it’s good to have something stuck in your teeth—good for science, anyway. New research on food particles clinging to two-million-year-old teeth reveal Australopithecus sediba, a possible ancestor of the genus Homo, had unusual dining habits for a hominid: The species consumed wood.

Discovered in South Africa in 2010, A. sediba is known from two partial skeletons. To reconstruct the species’ diet, Amanda Henry of the Max Planck Institute for Evolutionary Anthropology in Germany and colleagues relied on three methods. First, they looked at the markings on molar surfaces made by food as it’s being chewed. This analysis showed A. sediba ate hard objects,just as the South African hominid Paranthropus robustus did.

Next, the team looked at the carbon chemistry of the teeth. As a tooth forms, it takes up carbon from the food an individual eats. Forest plants such as trees, fruits and leaves (called C3 plants) have a different ratio of carbon isotopes than does grassland vegetation (C4 plants). The carbon in the teeth of A. sediba indicates the hominid dined almost exclusively on C3 plants, making it similar to some modern chimpanzees. Other early hominids likewise preferred C3 plants, but also included at least some C4 vegetation in their diet.

Finally, the researchers scraped off some of the dental plaque from two teeth of one of the known A. sediba skeletons. In the plaque were plant phytoliths, microscopic silica structures that form in plant cells. Different plants have distinctively shaped phytoliths, allowing scientists to use the structures to infer what ancient animals were eating. The team found 38 phytoliths, the first ever recovered from an early hominid. The phytoliths show A. sediba ate some water-loving C3 grasses and sedges as well as fruit, leaves and bark or wood. It’s the first evidence of a hominid eating wood, the researchers report in Nature.

The evidence of wood eating comes from just one individual, so it’s hard to know if this behavior is representative of the whole species. But the researchers point out the apparent reliance on wood and other forest plants fits with the skeletal evidence that suggests A. sediba climbed trees. Anthropologists have often suggested early hominids retained climbing abilities so they could find safe sleeping spots in the treetops. But maybe A. sediba was up there looking for breakfast, lunch and dinner.

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