Enamel Thickness in Atapuerca Homo antecessor and Sima de Los Huesos Permanent Premolars

OBJECTIVES: This study investigates premolar tissue proportions in the Atapuerca hominins to assess whether Homo antecessor (TD6) and Sima de los Huesos (SH) specimens exhibit thick or thin enamel, and whether relative enamel thickness is linked to tooth size reduction or enamel–dentine junction (EDJ) complexity. It also examines intrapopulation variability and provides new comparative data. MATERIALS AND METHODS: New 2D and 3D tissue metrics were derived from mCT images for TD6 (P3 = 2, P4 = 1), SH (P3 = 7, P4 = 6, P3 = 12, P4 = 17), Neanderthals (P3 = 4, P4 = 4, P3 = 4, P4 = 6), and modern humans (P3 = 15, P4 = 12, P3 = 26, P4 = 20). These data were combined with published sources for analysis. RESULTS: Our results suggest different patterns for upper and lower premolars in SH; upper premolars resemble those of Neanderthals, while lower premolars are more similar to modern humans. TD6 upper premolars show high variability, but the lower ones align more closely with Neanderthals. Relative enamel thickness varies with crown size, but not with EDJ complexity. DISCUSSION: Our findings highlight notable intrapopulation variability in enamel thickness among Atapuerca hominins and support the early emergence of reduced enamel in European populations. Moreover, our results imply that overall crown reduction may contribute to variation in enamel thickness in these populations. These results caution against using enamel thickness alone for taxonomic classification and emphasize the importance of analyzing both upper and lower dentitions across all dental classes.