Saturday, May 14, 2011

A. boisei Ate Soft Foods

Now it looks like there is evidence that the hyper-robust Australopithecus boisei did not survive on a diet of nuts and berries, as has been thought for decades. New research by Thure Cerling suggests that their primary subsistence was on grass, instead. On the other hand, the LiveScience article by Jeanna Bryner notes:
An early human with a big mouth made for chomping strangely preferred to eat soft, squishy fruits, new dental analyses suggest.

The finding — the big guy's teeth showed only light wear — might force scientists to downgrade everything they thought they knew about hominids' diets. For starters, the findings could cause this hominid,
Paranthropus boisei [or Australopithecus boisei], to relinquish rights to its long-held moniker, the Nutcracker Man, in the eyes of anthropologists.

The Nutcracker Man lived from about 2.3 million years ago to 1.2 million years ago, before vanishing from the fossil record. He boasted a huge jaw with massive chewing muscles and flat, tough teeth whose
crushing power could obliterate the roots and nuts of his home on the African savanna.
This is in stark contrast to the recent article by Cerling et al., which states very clearly:
Carbon isotope studies of P. robustus from South Africa indicated that it consumed some plants using C4 photosynthesis such as tropical grasses or sedges, but were also consistent with most of its dietary carbon (approximately 70%) having been derived from the C3 food items favored by extant chimpanzees (Pan troglodytes) such as tree fruits. In contrast, stable isotopes measurements of two P. boisei specimens from Tanzania suggested a high component of C4 biomass in its diet...1
In this case, C4 biomass is grasses and sedges. The PLoS article advocating the fruit position by Ungar et al. has this to say:
While the craniodental functional morphology Paranthropus boisei suggests an ability to generate and dissipate forces associated with the consumption of extremely hard or tough foods, microwear texture analysis offers no evidence that these hominins regularly did so.2
They list as a possibility that boisei ate fruit and suggest that it may have practiced a diet like the modern gorilla.

At this point, the only thing the two papers seem to have in common is that A. boisei ate softer foods than A. robustus. It will still have to necessitate a subsistence model change for this hominin.

Articles cited:

1Cerling, T. E., Mbua, E., Kirera, F. M., Manthi, F. K., Grine, F. E., Leakey, M. G., et al. (2011). Diet of Paranthropus boisei in the early Pleistocene of East Africa. Proceedings of the National Academy of Sciences.
doi: 10.1073/pnas.1104627108

2Ungar, P. S., Grine, F. E., & Teaford, M. F. (2008). Dental Microwear and Diet of the Plio-Pleistocene Hominin Paranthropus boisei. PloS one, 3 (4), e2044.
doi: 10.1371/journal.pone.0002044

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