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Hominid Feeding Biomechanics

Computer-generated model showing compressive stress in the cranium of Australopthecus africanus, an extinct early human that lived around 2.5 million years ago, imposed by biting on premolar teeth. Bright colors correspond to high stresses and indicate that a bony pillar running alongside the opening of the nasal cavity acts as a strut that structurally reinforces the face against premolar loads.

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Mark Spencer, an assistant professor at the Arizona State University (ASU) Institute of Human Origins, and Caitlin Schrein, a doctoral student at ASU's School of Human Evolution and Social Change, were part of an international team of researchers who studied the feeding biomechanics and dietary ecology of Australopithecus africanus, a relative of modern humans that lived about 2.5 million years ago.

Using state-of-the-art computer modeling and simulation technology, the same kind that engineers use to simulate how a car reacts to forces in a front-end collision, the researchers built a virtual model of an A. africanus skull and were able to see just how the jaw operated and what forces it could produce.

Researchers first took a cat (CT) scan of an A. africanus skull, discovered in 1947 and the most complete specimen they had. The skull had struts on the side of the nose but no teeth. Next, they meshed the data from the CT scan with data from another specimen with teeth to make a virtual model of the bone and tooth structure.

"Then we looked at chimpanzees, who share common features with Australopithecus, and took measurements of how their muscles work and added that to the model," said Spencer, who was lead investigator on the project. They validated the model by comparing it to a similar model built for a species of monkey called macaques. The result is a rainbow-colored virtual skull that illustrates forces absorbed by the cranial structure in simulated bite scenarios and how the unusual facial features of A. africanus were ideally suited to support the heavy loads of cracking hard nuts. Human skulls, on the other hand, have small faces and teeth and are not well-equipped to bite down forcefully on hard objects.

Results from the study reinforce the idea that facial specializations in early human species were adapted due to specialized diet. "The enlargement of the premolars, the heavy tooth enamel and the evidence now that they were loading forcefully on the premolars suggest the size of the objects were larger than the previously hypothesized small seeds and nuts," said Spencer.

During periods of climate change when food was scarce, early human species could rely on hard nuts and seeds. "Our research shows that early, pre-stone tool human ancestors solved problems with their jaws that modern humans would have solved with tools," added Spencer. [Results published in the February 2009 Proceedings of the National Academy of Sciences (PNAS) for research funded in part through the NSF funded project "Collaborative Research: Integrative Analysis of Hominid Feeding Biomechanics." Additional funding provided by the European Union.] (Date of Image: 2008)

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Credit: Simulation courtesy of Arizona State University and the "Hominid Feeding Biomechanics" research team

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