Covariation between cranial vault thickness and endocast shape in present-day humans and Neanderthals

While cranial vault thickness (CVT) is often used to discuss the taxonomic assignment of fossil specimens within the human lineage, the evolutionary processes accounting for its variation remain elusive. Numerous hypotheses have been proposed to interpret CVT arrangements, whether they relate to systemic, metabolic, biomechanical, allometric factors and/or to brain evolution. As they reach similar brain volumes via different developmental trajectories, comparing the CVT of present-day humans and Neanderthals allow us to evaluate whether brain development is likely to affect CVT. Here we document the CVT arrangements among these two groups and we test if differences are likely to be explained by variation in brain shape. We have used a sample of computed-tomographic scans consisting of 75 present-day humans and 6 Neanderthal adult individuals. Their respective endocranial shapes were quantified using landmarks and semilandmarks-based geometric morphometrics. The CVT was calculated at different semilandmarks positions and the cubic root of the endocranial volume was used for standardizing size in each measurement. Finally, the covariation between the shape of the endocast and CVT measurements was subsequently explored via two-block partial least squares analysis. Our results demonstrate that Neanderthals tend to display a thicker cranial vault, but this variation is still comprised within the range of present-day humans. The distinctive globular shape of present-day humans is characterized by thinner parietal walls. These results suggest that the differences in brain development in these two groups partly explain their respective CVT arrangements

Caractérisation de la mandibule et des dents de l’enfant gravettien de Gargas, France

International audienceWhile affinities and interactions between archaic and modern human populations (i.e. 200,000-40,000 BP in Eurasia) at macro-evolutionary and continental scales have received considerable attention, there has been less emphasis on the population history of Europe between 40,000 and 26,000 BP (i.e. prior to the Last glacial Maximum, LGM) when only modern humans were present. Here we examine the immature mandible from Gargas (France, ca. 29,000 cal BP), which displays a modern morphology overall with some archaic features rarely seen, if at all, in European Pleistocene and Holocene modern humans. In particular, the Gargas child has a very broad mandible, large tooth crowns with extreme deciduous and permanent mesiodistal molar diameters and a deciduous first molar with a quantity of enamel never previously reported. Furthermore, this child exhibits a supernumerary permanent tooth in the incisor region, a rare congenital disorder so far described for only five other pre-LGM modern humans. Finally, our results also highlight previously undocumented spatial differences in the tooth crown dimensions of Upper Palaeolithic fossils.Alors que les affinités et les interactions entre les populations humaines archaïques et modernes sont largement évaluées à des échelles macroévolutives et continentales (i.e. 200 000-40 000 BP en Eurasie), peu d’accent est mis sur l’histoire de la population européenne entre 40 000 et 26 000 BP (i.e. avant le dernier maximum glaciaire, LGM) lorsque seuls les humains modernes étaient présents. Ici, nous examinons la mandibule immature de Gargas (France, ca. 29 000 cal BP) qui présente une morphologie globale moderne avec des caractéristiques archaïques rarement ou jamais vues chez les humains modernes du Pléistocène européen et de l’Holocène. En particulier, l’enfant de Gargas présente une très grande largeur mandibulaire, de grandes couronnes dentaires avec des diamètres mésiodistaux extrêmes pour les molaires déciduales et permanentes, et une quantité importante d’émail pour sa première molaire déciduale précédemment inconnue. De plus, cet enfant présente une dent permanente surnuméraire dans la région incisive, un trouble congénital rare décrit pour au moins cinq autres humains modernes pré-LGM. Enfin, nos résultats ont également mis en évidence des différences spatiales auparavant non documentées dans les dimensions des couronnes dentaires des fossiles du Paléolithique supérieur