Newswise — While theories about what human ancestors ate abound, until now few methods existed for testing these models. A University of Arkansas professor and his colleagues have created methods for examining modern-day teeth and fossil teeth for indications of diet by using Geographic Information Systems (GIS) software and laser technology and have unearthed an anatomical shift in the fossil record that points to a change in the diet of early human ancestors — possibly a shift to eating more tough foods, such as meat.
"Teeth are perfect for testing diet hypotheses, because they are the best preserved items in the fossil record and are part of the digestive system," said Peter Ungar, professor of anthropology. "But until now, we haven't had the technology to pull much information out of them."
Teeth tell dietary tales in different ways: by their shapes, which offer insights into what they were designed to chew, and by microscopic wear and tear — the pits and scratches made by food as animals masticate. Researchers can study the dietary habits of modern-day primates, take molds of their teeth and compare the shapes and microscopic wear to that of human ancestors to form an idea of what they ate.
For years, researchers have measured tooth shape by hand and examined the microscopic wear and tear on teeth by counting and measuring hundreds of scratches on black and white photographs taken with an electron microscope — both methods leaving lots of room for error. Tooth shape changes as animals age — crests and peaks become less steep over time, and more difficult to measure accurately by hand. And counting pits and scratches using photographs rarely turns up consistent results.
To get a more detailed, accurate look at the shape of teeth, Ungar turned to software commonly used on a global level " GIS. He uses a special type of GIS software coupled with high-resolution laser scanning to examine the "dental landscapes" of teeth. A laser reads the three-dimensional coordinates of the tooth at one-thousandth-inch slices along the surface. The software then calculates coordinates and produces a three-dimensional map of the tooth.
This new technique, dental topographic analysis, focuses on worn teeth, allowing the reconstruction of the diets of more fossil species than ever before.To measure microwear on teeth, Ungar uses a white light scanning confocal microscope, which uses reflected white light to create an image based on measurements of the surface.
"The instrument gives you elevation information for the surface at a very high resolution, less than a millionth of an inch," Ungar said. The detailed, three-dimensional information also allows researchers to determine characteristics of the surface, such as roughness and directionality of the wear using fractal analyses borrowed from mechanical engineering. Plus, different laboratories using similar equipment get identical results, Ungar said.
Ungar and his colleagues have used some of these developing technologies to compare the slope and relief of two early human ancestors " Australopithecus afarensis, the Lucy species, and early Homo, the first members of the human genus. Their analysis showed that Australopithecus afarensis had shallow slopes on their teeth, suggesting a diet of brittle foods like nuts, seeds, roots and tubers. But the teeth of early Homo showed steeper slopes with greater shearing power than the teeth of Australopithecus afarensis, suggesting a dietary shift to tougher foods—possibly meat.
Archeological evidence has argued for the consumption of meat by early human ancestors, but Ungar's work has provided the first anatomical evidence that might support that hypothesis.
"The models are fine in and of themselves, but we need to go further," Ungar said. "We need to test the hypotheses." The new technologies being developed at the University of Arkansas will allow scientists to do that.