A new calculation of the ancient hominins' bite has determined that they possessed jaws and teeth larger and more powerful than those of their ape ancestors, which helped them to crack tough nuts and seeds.
According to a report in New Scientist, the study, led by David Strait, a palaeoanthropologist at the University of Albany in New York, indicated that these hominids boasted mouths ideal for accessing well-protected food.
Some researchers see the australopithecine mouth as sculpted for munching small, hard objects such as seeds, while others have argued that their bigger mouths merely allowed them to eat more food with each bite.
However, the new results cast doubt on both explanations.
Rather than analyze microscopic cracks in tooth enamel or the chemical composition of bone, as others had done, Strait's team took an approach more common to mechanical engineering.
Using a CT scanner, his team measured jaw bones and teeth from Australopithecus africanus, a species that flourished in southern Africa between 3.3 and 2.5 million years ago.
Then, with estimates of muscle strength, the researchers calculated the maximum force that each tooth could exert before shattering.
"We're taking a method that engineers use to build bridges, and we're using that method to examine the biomechanics of the face," said Strait.
These calculations suggest that A. africanus's premolars, which are teeth just behind the sharper canines, were strong enough to crush the shells of nuts that would have been too large to fit between the even more powerful molars further back in the mouth.
"Nuts and large seeds probably weren't Australopithecus' favorite snack, but munching on these foods might have helped them survive lean months or years, when sweet, soft fruits weren't around," Strait said.