Molar macrowear analysis to unveil dietary habits in Sima de los Huesos population

Abstract

The importance of determining hominin diet lies in its relationship with the morphological evolution of the masticatory apparatus. According to isotopic reports, the early Neanderthals from Atapuerca-Sima de los Huesos (SH) site, dated to 448±15 ka [1], probably relied on a rich-protein diet [2], as previously suggested for Neanderthals. In addition, the microwear analysis of the posterior dentition of SH suggested that this population also exploited other resources such as plant foods [3]. By analysing the occlusal macrowear in maxillary molars, this study explores the dietary ecology of this Middle Pleistocene population that likely lived during the MIS 12, one of the coldest periods recorded globally, that in the Iberian Peninsula caused a significant increment in semi-desert vegetation [1]. We employed the Occlusal Fingerprint Analysis (OFA) method [4], a digital approach that allows to reconstruct the individual masticatory behaviour through the analysis of occlusal wear facets. We examined seven maxillary first molars characterised by a moderate degree of tooth wear. The SH group is characterised by a macrowear pattern with large buccal phase I facets (41%), followed by lingual phase I (29%) and phase II (28%) facets. This pattern is similar to those of Neanderthals who inhabited temperate forests. The comparative analysis (One-way PERMANOVA, N permutation=9999, p=0.0001), further confirms this result, showing significant differences with Eurasian Pleistocene groups from Mediterranean and steppe/coniferous forest areas, but not with Neanderthals from deciduous woodlands. The results of this preliminary study suggest that the SH population exploited both animal and plant foods. The presence of larger buccal phase I facets in maxillary molars, as those displayed by the SH group, is associated with a diet dominated by animal proteins [5]. Moreover, the high proportion of lingual phase I facets indicates an increase in transverse mandibular movements, generally associated with the consumption of hard and abrasive foods, including roots, seeds, gums, and other plant materials [5]. Consequently, the large lingual phase I facets displayed by the SH group would indicate that this population exploited plant material as well. It is possible that the SH population relied on the consumption of underground storage organs, which are available year-round and are rich in carbohydrates. Our result is in agreement with the previous reports on isotopic [2] and tooth microwear analyses [3] that suggested that SH mainly relied on a diet rich in animal foods but also exploited hard and poorly processed plant resources, such as tubers, stems and seeds.