Inter- and intrapopulation variability of dental tissue proportions of European and African modern human populations’ permanent canines

Numerous studies have shown that human dentition traits vary both between and within populations. However, there is still little knowledge about how dental tissue proportions differ between modern human groups. In this study, two samples of European and African individuals were compared to assess the possible differences and similarities present in the dental tissue dimensions of their permanent canines. For this purpose, the volumes and surface areas of the coronal dentine and pulp complex and the enamel cap of 127 canines were measured by microcomputed tomography. The results show the existence of interpopulation variability in the dental tissue pattern of both samples, which is mainly due to the presence of a larger enamel component in the African population, while dentine seems to play a less critical role in the differences described between both dental samples. We also observed a similar pattern of sexual dimorphism in the dental tissue proportions of European and African canines, but in this case, the intrapopulation variability was mainly due to the presence of a greater dentine component in males. Therefore, because the dimensions of dental tissues vary at both inter- and intrapopulation levels in modern human groups, our results highlight the importance of selecting comparative samples that are geographically mixed and sex-balanced for future paleoanthropological investigations on dental tissue patterns of extinct and extant species to avoid overestimating or underestimating any possible similarities or differences.

Crown tissue proportions and enamel thickness distribution in the Middle Pleistocene hominin molars from Sima de los Huesos (SH) population (Atapuerca, Spain)

Dental enamel thickness, topography, growth and development vary among hominins. In Homo, the thickness of dental enamel in most Pleistocene hominins display variations from thick to hyper-thick, while Neanderthals exhibit proportionally thinner enamel. The origin of the thin trait remains unclear. In this context, the Middle Pleistocene human dental assemblage from Atapuerca-Sima de los Huesos (SH) provides a unique opportunity to trace the evolution of enamel thickness in European hominins. In this study, we aim to test the hypothesis if the SH molar sample approximates the Neanderthal condition for enamel thickness and/or distribution. This study includes 626 molars, both original and comparative data. We analysed the molar inner structural organization of the original collections (n = 124), belonging to SH(n = 72) and modern humans from Spanish origin (n = 52). We compared the SH estimates to those of extinct and extant populations of the genus Homo from African, Asian and European origin (estimates extracted from literature n = 502). The comparative sample included maxillary and mandibular molars belonging to H. erectus, East and North African Homo, European Middle Pleistocene Homo, Neanderthals, and fossil and extant H. sapiens. We used high-resolution images to investigate the endostructural configuration of SH molars (tissue proportions, enamel thickness and distribution). The SH molars exhibit on average thick absolute and relative enamel in 2D and 3D estimates, both in the complete crown and the lateral enamel. This primitive condition is shared with the majority of extinct and extant hominin sample, except for Neanderthals and some isolated specimens. On the contrary, the SH molar enamel distribution maps reveal a distribution pattern similar to the Neanderthal signal (with thicker enamel on the lingual cusps and more peripherally distributed), compared to H. antecessor and modern humans. Due to the phylogenetic position of the SH population, the thick condition in molars could represent the persistence of the plesiomorphic condition in this group. Still, more data is needed on other Early and Middle Pleistocene populations to fully understand the evolutionary meaning of this trait.