Wednesday, February 04, 2009

Australopithecus Had Jaws of Steel

The feeding biomechanics and dietary ecology of Australopithecus africanus. D. S. Strait, et al. 2009. PNAS. published online before print February 2, 2009.

Compressive stress in the cranium of Australopithecus africanus, an extinct early human, imposed by biting on the 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.

New research reveals nut-cracking abilities in our 2.5-million-year-old relatives that enabled them to alter their diet to adapt to changes in food sources in their environment.
Using state-of-the-art computer modeling and simulation technology – the same kind engineers use to simulate how a car reacts to forces in a front-end collision – evolutionary scientists built a virtual model of the A. africanus skull and were able to see just how the jaw operated and what forces it could produce.

"We started with a CT scan of a skull that is one of the most complete specimens of A. africanus that we have," said Mark Spencer, researcher in ASU's Institute of Human Origins and a lead investigator on the project. This would be a later ancestor of Lucy – STS5 - who is affectionately known as "Mrs. Ples." The skull, discovered in 1947, has struts on the side of the nose, but no teeth. "We meshed those data with another specimen with teeth to make the 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. We were able to validate this model by comparing it to a similar model built for a species of monkey called macaques," Spencer explained.

The result illustrates forces absorbed by the cranial structure in simulated bite scenarios and how their unusual facial features were ideally suited to support the heavy loads of cracking hard nuts.

"This reinforces the body of research indicating that facial specializations in species of early humans are adaptations due to a specialized diet," said Spencer. "The enlargement of the premolars, the heavy tooth enamel and the evidence now that they were loading forcefully on the molars suggest the size of the objects were larger than the previously hypothesized small seeds and nuts. link