Paranthropus boisei (nicknamed ‘nutcracker man’), a hominid living from 2.3 to 1.2 million years ago, was long thought to have had a diet consisting mainly of nuts and seeds. It certainly had the massive jaws and molars required to tackle that sort of fare. However, new research on P. boisei’s fossilized teeth has shown that the hominids were mis-nicknamed. In fact, the creatures ate mostly grasses.
Thure Cerling of the University of Utah and his colleagues from the University of Colorado, Stony Brook University, the Turkana Basin Institute, and the National Museums of Kenya used carbon isotope ratios to determine what the animals ate.
Plants use different metabolic pathways to incorporate carbon into their cells, and thus into the entire food chain. Briefly, C3 carbon fixation (used by about 95% of the plants on Earth) results in a different ratio of the isotopes carbon-12 and carbon-13 than does C4 carbon fixation (used mainly by grasses and sedges). Cerling’s team found that the carbon isotope ratios in 24 teeth from 22 different P. boisei individuals indicated that the creatures’ diets was about 77% C4 plants. This is comparable to grass-eaters of the time, such as the ancestors of modern zebras.
Meanwhile, Peter Ungar and his colleagues from the University of Arkansas examined microscopic scratches and wear patterns in the enamel of the P. boisei teeth. These too indicate a pattern of dining on grasses, rather than of cracking nuts or other hard objects. Taken together, we have strong evidence that at least one member of the hominid family was competing with the local cows at the dinner table.
You can see explanations by Peter Ungar in the following two clips, both from the National Science Foundation.