Using a powerful microscope and computer software, a team of scientistsfrom Johns Hopkins, the University of Arkansas, Worcester PolytechnicInstitute and elsewhere has developed a faster and more objective wayto examine the surfaces of fossilized teeth, a practice used to figureout the diets of our early ancestors.
By comparing teeth from two species of early humans,Australopithecus africanus and Paranthropus robustus, the researchersconfirm previous evidence that A. africanus ate more tough foods, suchas leaves, and P. robustus ate more hard, brittle foods. But they alsorevealed wear patterns suggesting that both species had variable diets."This new information implies that early humans evolved and alteredtheir diet according to seasonal and other changes in order tosurvive," said Mark Teaford, Ph.D., professor of functional anatomy andevolution at the Johns Hopkins School of Medicine.
The new approach to studying dental microwear, the microscopicpits and scratches on the tooth surface caused by use, offers a moreaccurate measurement of the surface's appearance and is described inthe August 4 issue of Nature.
"Paleontologists and physical anthropologists have had asomewhat naive view on diet, in part due to the limitations oftime-consuming, subjective approaches to analyzing teeth," saidTeaford. "So it's a huge step to have a reliable technology thatdetects subtler diet variations."
A team of scientists from the University of Arkansas andWorcester Polytechnic Institute developed the software, called"scale-sensitive fractal analysis," to analyze fossilized toothsurfaces through a confocal microscope, which allows three-dimensionalanalysis of an object. "You put the specimen in and the microscope isprogrammed to step down at fine intervals, perform its series of scans,and collect 3D coordinates for each data point," said Teaford. Theresult is like a map of the earth that shows mountains, valleys andplains in full relief, only at a microscopic scale.
As anticipated from traditional examination of fossilizedteeth, the tooth surfaces of P. robustus were more pitted and complex,while those of A. africanus were more scratched, with features oftenrunning in more uniform directions. However, according to Teaford, whoalong with researchers from the University of Arkansas, Stony BrookUniversity, and Pennsylvania State University carried out the dataanalysis, the study also revealed unexpected variability in the samplesfor each species and overlapping data for the two species. Theresearchers say this suggests that both species relied on their lesspreferred foods during periods of food scarcity. "If members of aspecies live in a seasonal environment, they can get all the soft fruitthey need during the wet season," Teaford added. "But come dry season,they may have to process something very hard or tough in order tosurvive."
"For years, it's been a dream of many researchers interested inour lineage to obtain this kind of information," continued Teaford."And the computer software is phenomenal, the heart and soul of thisproject. We now have a reliable technology to quickly and accuratelymeasure such surfaces." Teaford said future applications of thecomputer software include not only projects in paleontology andanthropology, but also engineering. "You could use it to examine thewear of metal surfaces on each other or to monitor clean surfaces at amicroscopic scale," said Teaford.
Besides Teaford, the authors of the paper are Robert Scott andPeter Ungar of the University of Arkansas; Torbjorn Bergstrom andChristopher Brown of Worcester Polytechnic Institute; Frederick Grineof State University of New York at Stony Brook; and Alan Walker ofPennsylvania State University.
Funding for the study was provided by the U.S. National ScienceFoundation. Curators at the U.S. National Museum of Natural History,the Transvaal Museum, and the University of the Witwatersrand suppliedfossil specimens, and AlejandroPérez- Pérez from the University of Barcelona helped prepare replicas.
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