Abstract
Mammalian tooth wear research reveals contrasting patterns seemingly linked to diet: irregularly pitted enamel surfaces, possibly from consuming hard seeds, versus roughly aligned linearly grooved surfaces, associated with eating tough leaves. These patterns are important for assigning diet to fossils, including hominins. However, experiments establishing conditions necessary for such damage challenge this paradigm. Lucas et al. (Lucas et al. 2013 J. R. Soc. Interface 10, 20120923. (doi:10.1098/rsif.2012.0923)) slid natural objects against enamel, concluding anything less hard than enamel would rub, not abrade, its surface (producing no immediate wear). This category includes all organic plant matter. Particles harder than enamel, with sufficiently angular surfaces, could abrade it immediately, prerequisites that silica/silicate particles alone possess. Xia et al. (Xia, Zheng, Huang, Tian, Chen, Zhou, Ungar, Qian. 2015 Proc. Natl Acad. Sci. USA 112, 10 669–10 672. (doi:10.1073/pnas.1509491112)) countered with experiments using brass and aluminium balls. Their bulk hardness was lower than enamel, but the latter was abraded. We examined the ball exteriors to address this discrepancy. The aluminium was surfaced by a thin rough oxide layer harder than enamel. Brass surfaces were smoother, but work hardening during manufacture gave them comparable or higher hardness than enamel. We conclude that Xia et al.'s results are actually predicted by the mechanical model of Lucas et al. To explain wear patterns, we present a new model of textural formation, based on particle properties and presence/absence of silica(tes).
Highlights
Several decades of observational research on the surface textures of tooth enamel has resulted in the establishment of reliable techniques for three-dimensional description of damaged enamel surfaces [1]
We conclude that Xia et al.’s results are predicted by the mechanical model of Lucas et al To explain wear patterns, we present a new model of textural formation, based on particle properties and presence/absence of silica(tes)
scanning electron microscope (SEM)–EDS analysis showed that the aluminium balls were coated with a very thin film
Summary
Several decades of observational research on the surface textures of tooth enamel has resulted in the establishment of reliable techniques for three-dimensional description of damaged enamel surfaces [1]. The marks made on tooth enamel could be due to dietary components and extraneous grit or (bits of) teeth themselves [3,4]. But statistical correlations have been found between patterns of dental microwear and diet that are thought to be a function of food material properties. It has been hypothesized that differences in food material properties are linked to patterns of jaw movement, which in turn influence the nature of the resulting microwear [1,6,7]. Dental microwear analysis has become a standard method of reconstructing diet in extinct vertebrates including fossil humans [8,9]
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