Deep changes in masticatory patterns and masseteric musculature configurations accompanied the eco-morphological evolution of cavioid rodents (Hystricognathi, Caviomorpha)

Abstract

Cavioids are one of the most eco-morphologically divergent clades among South American caviomorph rodents. In an unique way, they display three mandibular morpho-types which are linked to the relative positions and relations among masseteric muscles. The derived configuration present in Caviidae would be linked to a preponderance of grinding function during mastication. Oppositely, a greater vertical component in the plesiomorphic condition, observed in Dasyprocta and Cuniculus, could be linked to a likely predominant crushing function. These differences also are associated with changes in the direction of mastication; caviids have more propalinal movements of mandible whereas those taxa with the plesiomorphic morphology show more oblique movements. The sister clade of caviids represented by †Guiomys unica and †Prodolichotis pridiana, show relative high values of teeth scars inclination, indicating a slightly oblique mastication. Differences in masseteric configurations and masticatory patterns among cavioids would correspond mainly to variations in the diet, which in turn is related to the environmental conditions where each species lives. Caviids are mostly graminivorous/folivorous while dasyproctids and cuniculids have more frugivorous/folivorous diet. The plesiomorphic condition of the mandibular masseteric configuration is present in the oldest cavioids, from the first records in the Oligocene (about 33 Ma) while the derived condition is recorded from middle late Miocene (11.5 Ma), Based on the phylogenetic mapping of variables representing masseteric muscular structure and masticatory patterns we detected a potential association between the stepwise morphological evolution observed among cavioids with environmental changes occurred during Cenozoic era.