Dietary signals in dental microwear of predatory small mammals appear unaffected by extremes in environmental abrasive load

Abstract

Dental microwear texture analysis (DMTA) is a key proxy used to reconstruct the diets of extant and extinct animals. Causal agents of dental wear have been debated for decades, but the recent controversial suggestion that exogenous abrasives (or ‘grit’ particles) from the environment exert a greater influence on microwear formation than food items has led to renewed interest in this field of research. Feeding trials using large mammals suggest that DMTA can distinguish dietary differences despite variable grit loads. However, the effect of exogenous abrasives on the dental microwear of small, non-herbivorous mammals with quantified grit loads remains untested. Here, we examine dental microwear textures from the European mole (Talpa europaea), which provides an ideal test for the role of grit given moles' subterranean habitat and diet dominated by earthworms that contain, and are coated by, exogenous abrasives. We quantify the environmental abrasive load (by measuring silicate content of soils) and dietary abrasive load (by measuring silicate content of stomach contents) for moles from sites across Norfolk, UK to evaluate the effect of variation in grit loads on microwear textures. No significant relationships are found between microwear texture parameters and any metric of exogenous abrasive load, or between texture parameters and physical soil grit characteristics. Comparing mole microwear textures with those of bats, which have negligible environmental abrasive loads, reveals that moles are indistinguishable in multivariate texture-dietary space from bats that consume ‘soft’ prey, supporting suggestions that microwear textures preserve accurate dietary signatures and are not overwritten by wear from exogenous abrasives. Drawing upon examples from Jurassic mammaliaforms, we demonstrate the implications of these results for reconstructing the diets and habits of fossil mammals.