According to a study published in the open-access journal PLoS ONE, the ancient human ancestor species Paranthropus boisei did not actually eat the type of food that is suggested by the size and shape of its teeth. Professor of anthropology Peter Ungar (J. William Fulbright College of Arts and Sciences, University of Arkansas) and colleagues used microscopy and fractal analysis to analyze tooth marks on the ancient species. Their findings indicate that structure alone is not sufficient to determine what predecessors ate, and evolution could have dictated eating adaptations based on scarcity instead of on an animal's regular diet.

Ungar stated that, "These findings totally run counter to what people have been saying for the last half a century. We have to sit back and re-evaluate what we once thought."

Paranthropus boisei was an ancient hominin from between 2.3 million and 1.2 million years ago. He is known as the "Nutcracker Man" due to bigger and flatter cheek teeth and thicker enamel than any known hominin. Since 1959 when Mary and Louis Leakey wrote about the first specimen, it was believed that the hominin ate nuts, seeds, roots, and tubers that could be found on the savannas in eastern Africa. P. boisei had the teeth, cranium, and mandible that were seemingly designed to chew and crunch hard objects. "The morphology suggests what P. boisei could eat, but not necessarily what it did eat," Ungar said.

Usually, anthropologists analyze the size and shape of the teeth and jaws of human ancestors to determine what it ate. A microscopic investigation of the wear and tear on the tooth, however, can help researchers determine what the species actually ate. Ungar and his colleagues created a microwear texture analysis - 3-dimensional "point clouds" that show pits and scratches on the teeth - of the molars of seven specimens of P. boisei. Spanning a time frame of about 1,000,000 years, the specimens came from Kenya, Tanzania and Ethiopia.

Teeth were analyzed with respect to their complexity and directionality of wear texture - nuts, seeds, and other hard and brittle foods leave more complex tooth profiles and tough foods like leaves leave parallel scratches. Ungar and colleagues compared the dental microwear profiles of P. boisei to those of primates living today such as: grey-cheeked mangabeys and brown capuchins (that eat mostly soft items but can eat hard nuts or palm fronds in hard times) and the mantled howling monkey and silvered leaf monkey (that eat mostly leaves and other tough foods). In addition, the researchers compared P. boisei to contemporary hominids such as Australopithecus africanus (living from 3.3 million to 2.3 million years ago) and Paranthropus robustus (living from 2 million to 1.5 million years ago).

Finding that the P. boisei specimens had light wear, the researchers concluded that none of the individuals probably ate very hard or tough foods in the last days of their lives. The pattern is actually more similar to what is found in modern-day fruit-eating animals rather than in most modern-day primates. "It looks more like they were eating Jell-o," stated Ungar to highlight how this evidence contradicts what scientists previously thought that the species ate.

"If you give a gorilla a choice of eating a sugary fruit or a leaf, it will take the fruit every time," said Ungar. "But if you look at a gorilla's skull, its sharp teeth are adapted to consuming tough leaves. They don't eat the leaves unless they have to."

"This challenges the fundamental assumptions of why such specializations occur in nature," concluded Ungar. "It shows that animals can develop an extreme degree of specialization without the specialized object becoming a preferred resource."

Dental Microwear and Diet of the Plio-Pleistocene Hominin Paranthropus boisei
Ungar PS, Grine FE, Teaford MF
PLoS ONE (2008). 3(4): e2044.
doi:10.1371/journal.pone.0002044
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: Peter M Crosta

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