Postnatal shape changes in the rodent mandible at a macroevolutionary scale / Morgane Dubied

Postnatal shape changes in the rodent mandible at a macroevolutionary scale / Morgane Dubied, in colloque "1st Virtual Conference for Women Archaeologists and Paleontologists. Nouveaux apports à l’étude des populations et environnements passés" organisé par le laboratoire Travaux et Recherches Archéologiques sur les Cultures, les Espaces et les Sociétés (TRACES) de l’Université Toulouse Jean Jaurès et le laboratoire Paléontologie Évolution Paléoécosystèmes (PALEVOPRIM) de l'Université de Poitiers, sous la responsabilité scientifique de Julie Bachellerie, Ana Belén Galán López (Traces), Émilie Berlioz et Margot Louail (Palevoprim). Université Toulouse Jean Jaurès, 8-9 mars 2021. Session 1 : Morphological variability, taxonomy and adaptations.

Postnatal growth in mammals is a developmental period with important changes in skull and mandible functions. During the transition from the juvenile to the adult head, major biomechanical changes happen in relation to changes in the use of the masticatory apparatus around weaning, from sucking to gnawing andchewing movements. Mandible development is strongly interconnected with the muscle changes and tooth growth, much more than the skull that is constrained by additional functional demands. Epigenetic interactions are thought to integrate the different parts of the mandible by controlling the spatialization of bone formation and remodeling in response to biomechanical strain. Rodent is a very diverse and disparate mammal order, allowing to observe postnatal changes on a large scale. They are classified according to their mandible and muscle anatomies in three main suborders: myomorphs, hystricomophs and sciuromorphs. These suborders present a wide variety of mandible forms and various types of tooth growth (brachyodonty, hypsodonty, hypselodonty) or life-history traits. We performed 3D morphometric geometrics on juvenile and adult mandibles to model the postnatal changes at a macroevolutionary scale by analyzing variation of ontogenetic trajectories of mandible shape across 16 species of the three main suborders. We explored developmental morphospace and postnatal shape changes taking into consideration the phylogeny. A common developmental trend of the mandible was observed across rodents leading to an enlargement of the masseter fossae, in relation to the development of the masseter muscles during postnatal growth. Hypselodonty, the continuous growth of teeth, appears to have a special signature on the mandible development. The effects of muscle and tooth growths on postnatal trajectories suggest opportunitiesfor developmental plasticity in the evolution of the mandible shape. This may have differed across rodents, as the main patterns of postnatal growth vary between myomorphs and hystricomorphs and seem to be clade specific.