"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 – a rainbow colored virtual skull that 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.
"It was like watching 'Mrs. Ples' come to life," Spencer said.
"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.
"These fall-back foods – hard nuts and seeds – were important survival strategies during a period of changing climates and food scarcity," he added. "Our research shows that early, pre-stone tool human ancestors solved problems with their jaws that modern humans would have solved with tools."
Source: Arizona State University
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.
(Photo Credit: Simulation courtesy of Arizona State University and the "Hominid Feeding Biomechanics" research team)