Feeding ecology and chewing mechanics in hoofed mammals: 3D tribology of enamel wear.
Résumé
Large herbivorous mammals have evolved chewing systems capable of processing a large variety of structurally diverse foods. Three-dimensional (3D) surface texture parameters are applied to investigate wear mechanisms related to tooth morphology, food source, and chewing dynamics. We tested 46 industrial 3D surface texture parameters for their capability to robustly indicate specific biomechanics in two grazing (Blue Wildebeest and Grevy's Zebra) and two browsing (Giraffe and Black Rhinoceros) ungulate mammals. These species inhabit sub-Saharan Africa and represent foregut and hindgut fermenters. The results did not indicate a wavelength threshold that can consistently separate the structural (morphology) from the functional (diet) signals in the microtextures of the species studied. This implies that no structural signal is present at this scale. The most effective surface texture parameters for discriminating species with different diets are the parameters of height (Sa), functional (Smc, Sxp), volume (Vmc, Vv, Vvc, Vvv), density of furrows (medf), isotropy (IsT), and flatness (FLTt, FLTp, FLTq) of tooth surface textures. The surface textures of grazers are characterised by more anisotropy, higher height and volume values, more peaks and deeper furrows than browsers. In addition to discriminate between dietary preferences, surface texture parameters reflect the dynamic processes in the occlusal space that can scarcely be observed in situ. We found that during mastication, the occlusal gap is larger when the food consumed consists of more grasses and is smaller when browse is comminuted. With the narrowing of the occlusal gap, high peaks of surface texture are more likely to be ground down, either by attrition (tooth-tooth contact) or by fast fluid movements due to hydrodynamic pressures. A larger food bolus, in turn, is more likely to prevent peaks from being flattened. Thus, the surface texture parameters provide a tool set for understanding masticatory function directly at the enamel surface at a micrometre scale.