Dental tissue proportions and linear dimensions of Sima de los Huesos lower incisors

Abstract

Objectives: To assess the phenotypic affinities of the Sima de los Huesos (SH) mandibular incisors dental tissue proportions, and radicular dimensions, relative to Neandertals, recent modern humans (RMH), and a large comparative sample of Pleistocene hominins. Materials and Methods: Two dimensional (2D) and three dimensional (3D) data were extracted from SH (n = 22) incisors, and compared with specimens from Krapina (n = 6) and Ehringsdorf (n = 2), RMH (n = 42), as well as a comparative sample of hominins from the literature (n = 244). We calculated average enamel thickness (AET), relative enamel thickness (RET) and radicular variables (cervical area [CA] and root surface area [RSA], root linear dimensions [RL], dentine and pulp volume [RDV, RPV, TRV]). Results: We found that SH incisor crown variables were generally undiagnostic for 2D and 3D AET and 2D RET. Trends indicated thicker 3D RET in RMH relative to SH hominins, Tighenif hominins, and Neandertals. The SH and Neandertal mandibular incisors share similar RL, RSA, and root tissue volumes when compared to other extinct members of Homo. Relative to all other extinct hominins examined here, SH incisors display a relatively narrow cervical labio-lingual diameter. Finally, we found a weak correlations in SH and RMH between the crown and root variables. Discussion: This study confirms that SH mandibular incisors' dental tissue proportions and root dimensions align more closely to Neandertals. However, the complete set of Neandertal apomorphies is not present within SH mandibular incisors. SH incisors concur with traits reported in SH canines, and contrasting patterns in the molars, revealing a dichotomy between the anterior and posterior teeth for dental tissue proportions.