Enamel thickness topography and molar wear pattern in European early agriculturalists
Résumé
Enamel thickness (ET) has been demonstrated to be an evolutionary plastic trait, selectively responsive to dietary changes, wear and tooth function (e.g., Hlusko et al. 2004; Lucas et al. 2008; Schwartz 2000). European Late Paleolithic and Mesolithic hunter-gatherers mainly show flat wear pattern, while oblique molar wear has been reported as characteristic of early agriculturalists from the Neolithic (e.g., Smith 1984). Here we quantify molar wear patterns and ET topographic distributions in the French Neolithic necropolis from Gurgy, with the expectation that high masticatory forces on tooth location will lead to selection for greater ET. Gurgy has been used continuously around thousand years (ca. 5000-4000 cal. BC) and is situated at the crossroads of multiple cultural influences. As a comparative population having experienced other masticatory and/or dietary conditions, we used a French medieval sample. Occlusal wear was recorded in second upper permanent molars (UM2) of 64 Neolithic individuals and 311 comparative medieval UM2s. Using a microtomographic-based record (Skyscan 1076 X-ray microtomograph; voxel size: 17.93-36.18 µm3), we virtually assess ET topographic distribution in sub-samples of 17 Neolithic and 25 medieval UM2s. Differences in wear patterns and ET topography were found between the Neolithic and medieval samples. Oblique wear is largely dominant in the Neolithic sample (87%), while medieval UM2s show greater variation and only 41% of oblique wear. For the Neolithic population, maximal ET is precisely localized where occlusal wear is the most important, whereas medieval ET topography is more homogeneously distributed. These results suggest that ET could be affected by a selective pressure caused by functional dietary changes, notably by those reported for the transition to agriculture. Particularly, thick molar enamel may have evolved as a mean to resist wear. In this context, it is noteworthy that preliminary results in a small Mesolithic sample show relatively thin ET distributed homogeneously.