Do silica phytoliths really wear mammalian teeth?

Abstract

There is considerable literature suggesting that silica (opal) phytoliths cause dental enamel microwear in mammals. Much of this literature cites a single study from 1959 as evidence that silica phytoliths are harder than mammalian tooth enamel and so have the potential to cause dental microwear. No other studies using similar methodology have actually confirmed whether phytoliths are harder than dental enamel. The hardness of silica phytoliths from four species of grass and mammalian tooth enamel from sheep was tested using a modern nanoindentation tool. We found that silica phytoliths are considerably softer (51–211 Vickers Hardness, HV) than tooth enamel (257–397 HV) and therefore must be re-evaluated as a major source of dental microwear. The hardness results indicate that silica phytoliths do not contribute as much to mammalian dental microwear as previously reported and that exogenous grit and dust are a more likely cause. This premise has implications for interpretations of the causal agents of microwear phenomena in areas such as the evolution of high-crowned teeth in grazing mammals during the Miocene, and the inference of diet from fossilized mammal teeth as reported by some studies in physical anthropology and archaeology.