Ghislain Thiery

Chez les mammifères, les dents sont un outil essentiel à la fragmentation et à la fracture des aliments. En retour, les propriétés mécaniques des aliments exercent une pression de sélection sur la morphologie dentaire. L'objectif de ce mémoire est de déterminer si ce signal adaptatif peut être détecté à partir de la morphologie des molaires chez les primates actuels et fossiles. Dans ce cadre, la topographie dentaire 3D de 31 espèces de primates actuels est étudiée à l'aide d'une combinaison de variables classiques et originales. Un colobe fossile, Mesopithecus pentelicus du Miocène terminal de Pikermi (Grèce), est également analysé. Les résultats sont interprétés à partir du régime alimentaire mais aussi d'un système de catégorisation inédit évaluant le champ mécanique d'aptitude à cisailler, écraser et « craquer » les aliments.Les variables choisies permettent de distinguer de façon significative les catégories alimentaires et les champs d'aptitude au sein de l'échantillon actuel. Elles prédisent également que M. pentelicus avait une morphologie dentaire intermédiaire, et qu'il était apte à « craquer » des aliments durs tout en maintenant une adaptation à cisailler des aliments coriaces. En outre, les nouvelles variables permettent de montrer que les crêtes d'émail sont significativement plus tranchantes chez les espèces consommant des aliments coriaces, ce qui confirme leur utilisation en tant qu'outil de cisaillement. En revanche, la distribution de l'épaisseur de l'émail semble être plus homogène chez les espèces durophages, suggérant que la dent entière constitue l'outil élémentaire de « cracking » chez les primates.

This manuscript introduces trident, an R package for performing dental microwear texture analysis and subsequently classifying variables based on their ability to separate discrete categories. Dental microwear textures reflect the physical properties of the food, the feeding ecology of a given species, and niche partitioning when considering multi-specific communities. The trident package comes with independent functions and a user interface, trident, enabling easy and fast proficiency. It can import .SUR files, then remove aberrant peaks and possibly polynomial surfaces. Next, it can measure up to 24 texture parameters and their statistics of heterogeneity, generating 384 variables. It also ranks any number of variables using five different methods, displays the results in multivariate analyses, and exports the results into R, providing access to its large asset of libraries. We then present these features in three case studies, showing how trident helps answer questions commonly investigated by paleontologists and archaeologists. In the first case study, we separate four groups of domestic pigs based on their dietary composition. In the second case study, we identify microwear texture patterns in a large database of 15 primate species and relate these patterns to biomechanical and ecological factors. The third case study investigates the dental microwear textures of four extant ruminants to infer the diet of an extinct antelope from the Pleistocene of Greece. These case studies show how trident can leverage dental microwear texture analysis results.

The present 3D Dataset contains the 3D models analyzed in Assemat et al. 2023: Shape diversity in conodont elements, a quantitative study using 3D topography. Marine Micropaleontology 184.

Les molaires des mammifères jouent un rôle central lors de la mastication, ou la fragmentation des aliments par l’occlusion dentaire cyclique. Les mammifères fragmentent les aliments avec un degré d’efficacité variable en fonction de leur morphologie dentaire, cela suggère qu’il existe un lien adaptatif à estimer. Dans cette étude, nous testons l’effet de la morphologie des molaires lors de l’intercuspidation en occlusion centrée, c’est-à-dire entre les phases I et II, sur la fragmentation de cinq aliments qui correspondent à différents défis mécaniques rencontrés par les catarrhiniens. En utilisant un simulateur de mastication, nous mesurons expérimentalement le nombre de particules alimentaires produits après cinq intercuspidations successives pour deux forces différentes, afin d’évaluer leur influence. L’échantillon comprend des spécimens de cercopithèques et d’hominidés englobant les principaux modèles d’occlusion dentaire et les habitudes alimentaires des catarrhiniens actuels et fossiles. Nous montrons que l’augmentation de la force de morsure entraîne globalement une meilleure dégradation des aliments, mais des exceptions sont signalées notamment pour les aliments ductiles et coriaces (pommes, gingembres et feuilles). L’intercuspidation fragmente les aliments fragiles et complexes (noisettes et grillons). Cette expérience a permis de montrer que seules une occlusion et une force de morsure appropriées sont suffisantes pour fragmenter les aliments fragiles et que des mouvements supplémentaires sont nécessaires pour fragmenter les aliments coriaces (feuilles et herbes). Elle met également en évidence les capacités masticatoires de différents modèles d’occlusion chez les primates et notre capacité à les tester avec la robotique. Cette nouvelle avancée permettra d’étudier des questions anthropologiques majeures portant sur l’évolution de la morphologie dentaire.

Extant colobine monkeys are specialized leaf eaters. But during the late Miocene, western Eurasia was home to colobines which were less efficient at chewing leaves than they were at breaking seed shells. To understand the link between folivory and granivory in this lineage, the dietary niche of Mesopithecus delsoni and M. pentelicus was investigated in southeastern Europe, where a major environmental change occurred during the late Miocene. We combined dental topographic estimates of chewing efficiency with dental microwear texture analysis of enamel wear facets. M. delsoni was more efficient at chewing leaves than M. pentelicus, the dental topography of which matches an opportunistic seed eater. Concurrently, microwear complexity increases in M. pentelicus, especially in the northernmost localities corresponding to present-day Bulgaria. This is interpreted as a dietary shift towards hard foods such as seeds or tubers, which is consistent with the savanna and open mixed forest biomes that covered Bulgaria during the Tortonian. The fact that M. delsoni was better adapted to folivory and consumed a lower amount of hard foods than M. pentelicus suggests that colobines either adapted to folivory before their dispersal to Europe, or evolved adaptations to leaf consumption in multiple occurrences. This article is protected by copyright. All rights reserved

Objectives Topographic estimates of dental relief are now commonly used to make dietary inferences from the teeth of extant and extinct primates. We thoroughly compared commonly used relief estimates in an effort to help researchers decide which variable best suits their objectives. Materials and methods We combined a total of three datasets: five theoretical models built to compare the effect of tooth complexity and basin depth on relief estimates, a dataset of 110 lower molars of prosimians, and a dataset of 25 upper molars of apes. We investigated intra-mesh variation and tooth average relief, estimated from slope and three different relief indices, according to four criteria: (1) the ability to map relief on topographic maps, (2) the correlation with other relief estimates, (3) the ability to separate high-relief molars of folivores from deep-relief molars of insectivores in prosimians, and (4) the influence of surface complexity on relief estimates in apes. Results We found that polygon slope and relief index are linked by a mathematical relation. Tooth average slope and all relief indices are strongly correlated. In contrast, relief estimates are moderately correlated to cusp elevation. One relief index of four relief estimates had an excellent ability to separate high-relief from deep-relief molars in prosimians, whereas slope could not separate them. No significant effect of tooth complexity on dental relief could be detected in apes. Conclusions Because slope and relief indices are highly correlated, it is strongly recommended not to combine them in multivariate analysis. Still, slope and relief indices show interesting differences in scaling, graphical representation, computation method, and ability to separate high-relief and deep-relief molars. Our results also suggest that slope and relief indices can vary independently of tooth complexity and are moderately affected by mean cusp elevation in apes.

Enamel thickness is not uniform across the dental crown of primates. It has been suggested that enamel distribution could be used in taxonomy or for ecological inferences. For instance, the thickness of molar enamel in mammals consuming hard food is expected to be uneven, despite differing reports on extant and extinct apes. Overall estimations of average and relative enamel thickness may mask the details of enamel distribution in complex teeth such as molars. Investigating enamel distribution and its purported relationship with ecology or phylogeny would require more detailed assessments. This paper aims to assess whether apes that consume hard foods on a regular basis, such as Pongo pygmaeus, can be characterized by the evenness or unevenness of enamel thickness. To do so, we combined topographic maps and distribution histograms of enamel thickness with cumulative profiles of its variation, or “pachymetric profiles”. We investigated a sample of 25 unworn hominoid upper second molars scanned by X-ray microtomography, and further compared this to a sample of 32 cercopithecines and colobines. Topographic maps show uniformly thin enamel for Gorilla gorilla and Hylobates sp., unevenly thin enamel for Pan paniscus and Pan troglodytes, and unevenly thick enamel for Pongo pygmaeus. The skewness of enamel distribution does not distinguish between ape species, but does separate apes from OldWorld monkeys. Contrary to previous reports on OldWorld monkeys, the slope of enamel thickness profiles, or pachymetric slope, does not predict the diet of extant apes. However, it does separate the Pan genus, which is characterized by a higher pachymetric slope indicating more uneven enamel distribution compared to other apes. The uneven thickness of enamel distribution observed on topographic maps for P. pygmaeus is not supported by its low pachymetric slope, which instead indicates uniform enamel distribution. This discrepancy in the results obtained for P. pygmaeus can be interpreted as an evolutionary tradeoff between fine-scale versus overall enamel distribution. On the one hand, unevenly thick enamel at a fine scale, combined with strongly decussated enamel as observed in P. pygmaeus, is expected to increase local resistance to crack propagation. On the other hand, uniformly thick enamel at the overall scale would improve the overall resilience of the enamel in coping with challenging food on a daily basis. Although understanding the effects of ecology on enamel distribution in apes requires further investigation, the results presented in this paper confirm the interest of enamel distribution for taxonomy and phylogeny.