By comparing teeth from two species of early humans, Australopithecus africanus and Paranthropus robustus, the researchers confirm previous evidence that A. africanus ate more tough foods, such as leaves, and P. robustus ate more hard, brittle foods. But they also revealed wear patterns suggesting that both species had variable diets. "This new information implies that early humans evolved and altered their diet according to seasonal and other changes in order to survive," said Mark Teaford, Ph.D., professor of functional anatomy and evolution at the Johns Hopkins School of Medicine.
The new approach to studying dental microwear, the microscopic pits and scratches on the tooth surface caused by use, offers a more accurate measurement of the surface's appearance and is described in the August 4 issue of Nature.
"Paleontologists and physical anthropologists have had a somewhat naive view on diet, in part due to the limitations of time-consuming, subjective approaches to analyzing teeth," said Teaford. "So it's a huge step to have a reliable technology that detects subtler diet variations."
A team of scientists from the University of Arkansas and Worcester Polytechnic Institute developed the software, called "scale-sensitive fractal analysis," to analyze fossilized tooth surfaces through a confocal microscope, which allows three-dimensional analysis of an object. "You put the specimen in and the microscope is programmed to step down at fine intervals, perform its series of scans, and collect 3D coordinates for each data point," said Teaford. The result is like a map of the earth that shows mountains, valleys and plains in full relief, only at a microscopic scale.
As anticipated from traditional examination of fossilized teeth, the tooth surfaces of P. robustus were more pitted and complex, while those of A. africanus were more scratched, with features often running in more uniform directions. However, according to Teaford, who along with researchers from the University of Arkansas, Stony Brook University, and Pennsylvania State University carried out the data analysis, the study also revealed unexpected variability in the samples for each species and overlapping data for the two species. The researchers say this suggests that both species relied on their less preferred foods during periods of food scarcity. "If members of a species live in a seasonal environment, they can get all the soft fruit they need during the wet season," Teaford added. "But come dry season, they may have to process something very hard or tough in order to survive."
"For years, it's been a dream of many researchers interested in our lineage to obtain this kind of information," continued Teaford. "And the computer software is phenomenal, the heart and soul of this project. We now have a reliable technology to quickly and accurately measure such surfaces." Teaford said future applications of the computer software include not only projects in paleontology and anthropology, but also engineering. "You could use it to examine the wear of metal surfaces on each other or to monitor clean surfaces at a microscopic scale," said Teaford.
Besides Teaford, the authors of the paper are Robert Scott and Peter Ungar of the University of Arkansas; Torbjorn Bergstrom and Christopher Brown of Worcester Polytechnic Institute; Frederick Grine of State University of New York at Stony Brook; and Alan Walker of Pennsylvania State University.
Funding for the study was provided by the U.S. National Science Foundation. Curators at the U.S. National Museum of Natural History, the Transvaal Museum, and the University of the Witwatersrand supplied fossil specimens, and Alejandro Pérez- Pérez from the University of Barcelona helped prepare replicas.