Exploring the impact of soil ingestion on dental microwear textures using a wild boar experimental model

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Dental microwear has been widely used to reconstruct the diet of past mammals. However, understanding the respective impact of exogenous mineral particles on dental wear is an ongoing challenge. Among palaeontologists and evolutionary biologists, this topic is a key issue in the debate on the selective pressures driving dental phenotypes, such as molar hypsodonty in ruminants, molar lengthening in suids or enamel thickening in hominins. Among archaeologists, it can help better understand ancient herd-feeding systems. Particularly, few studies have shown that soil ingestion generates different microwear traces.To fill this gap, this study relies on the first large-scale controlled-food experiment on wild boars (Sus scrofa). It provides the opportunity to investigate the impact of natural soil ingestion over microwear traces by comparing penned wild boars that were able to root with stalled wild boars that were not. Dental microwear textures (DMT) variations were measured on 22 controlled-fed boars kept captive from 6 to 24 months old, either in an indoor stall with no soil ingestion (n=10), or in an outdoor wooded pen (n=12) with rooting behaviors and natural soil ingestion. We conducted particle size distribution analyses on two soil samples. They indicate that the soil is mainly composed of sand (38 %) and silt (43 %), with few clay fractions (19 %), which can be classified as a loam texture. We analyzed shearing and crushing facets of upper and lower first and second molars using two sets of texture parameters. In line with previous works, our results show that the consumption of exogenous abrasives in rooting boars leads to less rough and complex wear surfaces and more anisotropic than in stall-fed boars, even though they received the same diet. Thus, as previously stated, we highly recommend studying DMT when investigating ancient pig husbandry systems, particularly local changes in food management.