Measuring dental wear equilibriums—the use of industrial surface texture parameters to infer the diets of fossil mammals

Abstract

Inferring the diet of fossil mammals is a major approach to mammalian palaeobiology and palaeoecology. Dental wear provides a unique record of oral behaviour, available for most extant and fossil mammals. Dental wear facets are thus one of the immediate habitat interfaces allowing analysis of food selection, food availability, and dietary segregation in fossil and extant communities based on the same source of information. As any surface, wear facets can be described as a complex landscape with more or less elevated alterations. In order to describe technical surfaces, a system of surface roughness parameters is available, which are highly indicative statistical tools in characterizing surface micro texture in industrial applications. We test the hypothesis, that dental microwear can be described by established surface roughness parameters, and that these parameters can help to identify the dietary traits of fossil herbivores. We investigated three extant African bovid species, the greater kudu, the bushbuck and the hartebeest, which were selected because each of them represents one of the major dietary classes as browsers, mixed feeders and grazers, respectively. As a fossil species we investigated the upper Miocene hipparionine horse Hippotherium primigenium from the upper MN9 Dinotheriensande. A diamond stylus profiling instrument was used to measure surface roughness on four phase I shearing facets of upper molars. Discriminant analyses were performed to test 24 roughness parameters for their ability to predict dietary classes. Several parameters were identified as confidently separating the grazer and the browser in this comparison, while the mixed feeder is intermediate. For H. primigenium, we find a mixed feeding signal confirming earlier dietary reconstructions of the species based on mesowear and microwear. The degree of attrition in browsers is reflected by a high bearing ratio (RTp). In grazers, the lower bearing ratio reflects the striated and elevated topography of an abrasion dominated surface. The bearing ratio may be understood as immediately reflecting the position of the attrition–abrasion equilibrium, and thus bridging the two major methods of tooth based dietary evaluation, the microwear- and the mesowear method. Surface texture parameters are found to encapsulate information about basic dental function that we hypothesize has fundamentally driven dental adaptation in mammalian evolution.