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A brand new study in the open access journal PLoS One reports on the results of an analysis of the microwear on the teeth of Paranthropus boisei (also known as Australopithecus boisei). The results contest what we’ve all along assumed was going on with the form and the function of these robust australopithecine teeth. I even repeated this assumption in a recent post, discussing the dietary implications of a Neandertal.

The results indicate that marks on the teeth of Paranthropus boisei do not correspond with the size and shape of its teeth. This observation suggests that structure of the skull, mandible, and teeth are not enough to infer dietary preferences. Furthermore, evolutionary adaptation for eating may have been based on scarcity rather than on an animal’s regular diet.

The paper, “Dental Microwear and Diet of the Plio-Pleistocene Hominin Paranthropus boisei,” is authored by Peter Ungar, Frederick Grine, and Mark Teaford. Brian, from Laelaps, has written up a very excellent and thorough review of the research. You should check that out.

Why did the authors look at dental microwear on the surface of the teeth? They explain that dental microwear offers direct evidence of the mechanical properties of food item, and that makes a lot of sense. During mastication, the food an organism eats abrades with the surface of the teeth. The texture of the food may scratch and dent teeth, especially if really hard foods like nuts, roots, and tubers are chewed. Likewise, softer foods affect teeth less.

Based upon the size and morphology of Paranthropus boisei teeth, many previous researchers thought they ate tough foods. Hell, the type specimen for P. boisei has been nicknamed “Nutcracker Man.” They have saggital crests similar to gorillas They also have very large teeth with thick layers of enamel. Coupled with the massive jaws, many people thought that P. boisei consumed really dense, fibrous plants.

As I’ve said, the results of the microwear analysis indicates that P. boisei did not eat the hard abrasive foods that we thought they did. Using a confocal microscope, engineering software and scale-sensitive fractal analysis the authors analyzed the around 54 molars from seven specimens of P. boisei. These seven specimens came from different areas, Ethiopia, Kenya, and Tanzania, respectively. Also, these specimens cover over 1 million year of P. boisei existence. Any similarities or differences in the microwear on P. boisei teeth from these temporally and spatially different locations woulda screened out variations in diet reflected to time or environment.

For your viewing pleasure, the authors provided this photograph of detailing the degree of microwear of the teeth of the seven different specimens.

Here’s the legend: (A) KNM-CH 1, (B) KNM-ER 729, (C) KNM-ER 3230, (D) KNM-ER 3952, (E) KNM-WT 17400, (F) OH 5, (G) Omo L7A-125. Clearly you see scratches…

… But what Ungar et al. were looking for was the degree, complexity and directionality of wear textures. Again, hard, brittle foods like nuts and seeds tend to lead to more complex tooth profiles, while tough foods like leaves lead to more parallel scratches, which corresponds with directionality. Comparisons of the the dental microwear profiles of P. boisei to the microwear profiles of extant primates indicates they didn’t eat the same type of foods. Grey-cheeked mangabeys and brown capuchins sometimes rely on hard nuts or palm fronds, as do the mantled howling monkey and silvered leaf monkey. Also included in the comparison was microwear analysis on teeth of Australopithecus africanus.

The P. boisei teeth show light wear, suggesting that none of the individuals ate extremely hard or tough foods in the days leading up to death. The microwear patterns are more consistent with modern-day fruit-eating animals than with most modern-day primates. This conclusion is a fundamental shift in the way we think about the diets of early hominins.

Before you write off the anatomical and evolutionary mantra “form = function,” please consider this: I did not read any discussion on other possible causes for the lack of deep pitting from hard foods.

This is unfortunate. I wonder if the depth of the pits coulda have been buffed out over the millions years these fossils persisted? We know the fossilization process is a time intensive process, and many different weathering affects affect how surfaces of bone are preserved. Furthermore, many fossils are formed by being deposited in or around water sources. Water moves things, like rocks, wood, and bones. The abrasive edges of rocks are buffed down to smooth river stones over time. Couldn’t this have happened on a microscopic scale?

Yeah, I think it is certainly possible, even if the entire specimen, like OH 5, don’t show signs of massive weathering, we are talking about teeth that are very old. Teeth that were exposed could have been buffed out by other elements like wind, too. Suffice to say, many different things coulda happened to them to affect the degree of the abrasions. Comparing them to modern primate teeth is somewhat flawed because modern primate teeth haven’t been affected by the forces of nature for millions of years.

    Ungar, P.S., Grine, F.E., Teaford, M.F., Petraglia, M. (2008). Dental Microwear and Diet of the Plio-Pleistocene Hominin Paranthropus boisei. PLoS ONE, 3(4), e2044. DOI: 10.1371/journal.pone.0002044