RESEARCH ARTICLE Mechanical Properties of Plant Underground Storage Organs and Implications for Dietary Models of Early Hominins

Abstract The diet of early human ancestors has received renewed theoretical interest since the discovery of elevated d13C values in the enamel of Australopithecus africanus and Paranthropus robustus. As a result, the hominin diet is hypothesized to have included C4 grass or the tissues of animals which themselves consumed C4 grass. On mechanical grounds, such a diet is incompatible with the dental morphology and dental microwear of early homi-nins. Most inferences, particularly for Paranthropus, favor a diet of hard or mechanically resistant foods. This dis-crepancy has invigorated the longstanding hypothesis that hominins consumed plant underground storage organs (USOs). Plant USOs are attractive candidate foods because many bulbous grasses and cormous sedges use C4 photo-synthesis. Yet mechanical data for USOs—or any putativ