The analysis of marks on the teeth of members of an ancient human ancestor species has determined that structure alone is not enough to predict dietary preferences and that evolutionary adaptation for eating may have been based on scarcity rather than on an animal's regular diet.
The study was led by Peter Ungar, a University of Arkansas professor and his colleagues, who analysed marks on the teeth of the ancient human "cousin" known as the "Nutcracker Man", using a combination of microscopy and fractal analysis.
The research team found that what the ancient human actually ate does not correspond with the size and shape of its teeth.
The researchers examined the teeth of Paranthropus boisei, an ancient hominin that lived between 2.3 million and 1.2 million years ago and is known popularly as the "Nutcracker Man" because it has the biggest, flattest cheek teeth and the thickest enamel of any known hominin.
Till now, scientists have believed that P. boisei fed on nuts and seeds or roots and tubers found on the savannas throughout eastern Africa because the teeth, cranium and mandible appear to be built for chewing and crunching hard objects.
By looking at the patterns of microscopic wear on a tooth, scientists can get direct evidence for what these species actually ate.
Ungar and his colleagues used a combination of a scanning confocal microscope, engineering software and scale-sensitive fractal analysis to create a microwear texture analysis of the molars of seven specimens of P. boisei.
The specimens spanned a time frame of almost a million years and were found in Kenya, Tanzania and Ethiopia.
Using these techniques, the researchers were able to create three-dimensional "point clouds" that showed the pits and scratches on the teeth.
The researchers looked at complexity and directionality of wear textures in the teeth they examined.
They compared the dental microwear profiles of P. boisei to the microwear profiles of modern-day primates that eat different types of diets.
They also compared the microwear analysis to analyses of teeth from some of the fossil's more contemporary counterparts - Australopithecus africanus, which lived between 3.3 million and 2.3 million years ago, and Paranthropus robustus, which lived between 2 million and 1.5 million years ago.
The P. boisei teeth had light wear, suggesting that none of the individuals ate extremely hard or tough foods in the days leading up to death. It's a pattern more consistent with modern-day fruit-eating animals than with most modern-day primates.
"This challenges the fundamental assumptions of why such specializations occur in nature," said Ungar. "It shows that animals can develop an extreme degree of specialization without the specialized object becoming a preferred resource," he added.