Zanolli, Clément

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

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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)

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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.

Modern humans sex estimation through dental tissue patterns of maxillary canines

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Objectives Dental tissue proportions of human permanent canines is one of only a few sexually dimorphic features that is present in childhood and maintained in adults, offering the opportunity for this to be used in sex determination. This study assesses dental tissue volumes and surface areas of maxillary permanent canines in a sample of known sex to provide new data and to explore the potential of these variables as reliable sexual estimators. Materials and methods The teeth studied here derive from 56 individuals (27 females and 29 males) of known sex and age, and of different geographic origins. The teeth were scanned and three-dimensional (3D) measurements (volumes and surface areas) were obtained. In addition, a discriminant function analysis was applied. Results The results presented here concur with those previously published in relation to both size and dental tissue patterns. Male maxillary canines have a greater dentine component, whereas female enamel is thicker, leading to a difference in dental size in favor of males. Discriminant functions were calculated using these histological variables successfully identifying sex in between 87.5% and 93.75% of the known-sex hold-out sample, with 92.3% correctly assigned when all functions were applied together. Discussion The present study supports that methods for sex determination based on dental tissue measurements can achieve high allocation accuracies, being especially useful in the case of subadults or when no other appropriate method is available.

Tooth crown tissue proportions and enamel thickness in Early Pleistocene Homo antecessor molars (Atapuerca, Spain)

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Tooth crown tissue proportions and enamel thickness distribution are considered reliable characters for inferring taxonomic identity, phylogenetic relationships, dietary and behavioural adaptations in fossil and extant hominids. While most Pleistocene hominins display variations from thick to hyper-thick enamel, Neanderthals exhibit relatively thinner. However, the chronological and geographical origin for the appearance of this typical Neanderthal condition is still unknown. The European late Early Pleistocene species Homo antecessor (Gran Dolina-TD6 site, Sierra de Atapuerca) represents an opportunity to investigate the appearance of the thin condition in the fossil record. In this study, we aim to test the hypothesis if H. antecessor molars approximates the Neanderthal condition for tissue proportions and enamel thickness. To do so, for the first time we characterised the molar inner structural organization in this Early Pleistocene hominin taxon (n = 17) and compared it to extinct and extant populations of the genus Homo from African, Asian and European origin (n = 355). The comparative sample includes 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 TD6 molars (tissue proportions, enamel thickness and distribution). TD6 permanent molars tend to exhibit on average thick absolute and relative enamel in 2D and 3D estimates, both in the complete crown and the lateral enamel. This condition is shared with the majority of extinct and extant hominin sample, except for Neanderthals and some isolated specimens. However, while the total crown percentage of dentine in TD6 globally resembles the low modern values, the lateral crown percentage of dentine tends to be much higher, closer to the Neanderthal signal. Similarly, the H. antecessor molar enamel distribution maps reveal a relative distribution pattern that is more similar to the Neanderthal condition (with the thickest enamel more spread at the periphery of the occlusal basin) rather than that of other fossil specimens and modern humans (with thicker cuspal enamel). Future studies on European Middle Pleistocene populations will provide more insights into the evolutionary trajectory of the typical Neanderthal dental structural organization.

Contribution of dental tissues to sex determination in modern human populations

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Objectives Accurate sex estimation is an essential step for the reconstruction of the biological profile of human remains. Earlier studies have shown that elements of the human permanent dentition are sexually dimorphic. The aims of this study are to determine the degree of sexual dimorphism in the dental tissue volumes and surface areas of mandibular canines and to explore its potential for reliable sex determination. Method The teeth included in this study (n = 69) were selected from anthropological collections from Spain, South Africa and Sudan. In all cases, the sex of the individuals was known. The teeth were scanned and three-dimensional (3D) measurements (volumes and surfaces areas) were obtained. Finally, a dsicriminant function analysis was applied. Results Our results showed that sexual dimorphism in canine size is due to males having greater amounts of dentine, whereas enamel volume does not contribute significantly to overall tooth size dimorphism. Classification accuracy of the multivariable equations tested on slightly worn teeth ranged from 78 to 90.2% for the crossvalidation, and from 71.43 to 84.62% for the hold-out sample validation. When all functions were applied together, the sex was correctly assigned 92.30% of the time. Conclusions Our results suggest that the 3D variables from mandibular canine dental tissues are useful for sex determination as they present a high degree of dimorphism. The results obtained show the importance of 3D dental tissue measurements as a methodology in sex determination, which application should be considered as a supplemental method to others.