Newswise — Careful analysis of microscopic abrasions on the teeth of early human relatives by researchers at Stony Brook University, the University of Arkansas, and Johns Hopkins University show that although it was equipped with thick enamel, large jaws and powerful chewing muscles, this ancient species may not have eaten the nuts, seeds or roots their anatomy suggests. Instead, the tooth wear suggests a diet that consisted mainly of softer foods, as reported in next week's Public Library of Science One.

"We tend to operate under the assumption that the shape of an animal's teeth, jaws and skull tells us what they habitually ate," says Fred Grine, Professor of Anthropology and Anatomy at Stony Brook University. "However, our work has shown that we can be misled by the apparent obvious " just because an animal is capable of eating hard foods doesn't mean that it did so habitually " it really makes us rethink some of our basic assumptions."

Using high-powered microscopy to scan tooth surfaces and computer programs that measure imperfections on the surfaces of teeth, the researchers analyzed tooth surfaces from the extinct species Paranthropus boisei from East Africa. According to most researchers, the jaws and tooth structure of this human relative were so specialized and extreme it must have had a very specialized diet. In fact, its anatomy gave it the nickname "Nutcracker Man."

Measuring the microwear from permanent molars of P. boisei from Ethiopia, Kenya and Tanzania dating from 2.3 million years ago to about 1.4 million years ago, the team compared their results with microwear from living primates and other fossils. They found that Paranthropus boisei teeth had very little of the pitting that is indicative of eating hard foods.

"It seems that while they were certainly capable of eating harder foods, they generally didn't, do so" says Grine. "We see similar situations in modern primates, who often like soft fruit. But they can't find that all the time, so occasionally they'll eat harder or tougher foods if they have to, especially during those times of the year when their preferred foods are simply unavailable."

Adds Grine, "When you look at the skull of Paranthropus boisei you think 'now this is a real chewing machine " a veritable walking Cuisinart,' but that's clearly an oversimplification."

The research was funded by the National Science Foundation.

The authors of the paper are Peter Ungar, University of Arkansas, Frederick Grine of Stony Brook University and currently on sabbatical at the University of Cambridge, UK, and Mark Teaford of Johns Hopkins.

Photo captions:

1) "boisei skull oblique" Paranthropus boisei male skull from Olduvai Gorge (found by Mary Leakey in 1959). It shows the large crest on the top of the skull for the attachment of chewing muscles, etc.

2) "boisei-human molar comparison" " Paranthropus boisei mandible with its third molar (wisdom tooth) compared to a modern human mandible for size. What is even more remarkable, is that these creatures were probably on average smaller than modern humans.

3) "boisei occlusal don" This is a photograph of the upper teeth in the P. boisei skull from Olduvai Gorge (seen in picture 1 above), showing the huge premolars and molars. Photo credit: Donald Johanson.