Inner ear morphology in carnivoran mammals
Résumé
The inner ear is the organ of hearing and balance in vertebrates. The bony labyrinth, surrounding the soft tissues of the inner ear, is often used as proxy to investigate the inner ear morphology and evolution. Because of its fundamental role in coordinating movements, morphological differences of the inner ear between species and across groups have been shown to reflect phylogenetic relationships and locomotor specializations.
We used high resolution X-ray microtomography to reconstruct virtually the bony labyrinth of extant carnivoran mammals, including top predators such as bears, lions, wolves and seals. We placed 126 landmarks and semi-landmarks across the 3D bony labyrinth models. We performed 3D geometric morphometrics analyses to test the potential link between inner ear morphology, phylogenetic relatedness and locomotor specializations of species, in particular for aquatic and cursorial adaptations. We found that the whole bony labyrinth morphology bears a significant phylogenetic signal in carnivorans: the size and curvature of the semicircular canals, angles between canals, presence or absence of a secondary common crus, degree of lateral compression of the vestibule, orientation of the cochlea relative to the semicircular canals, proportions of the cochlea, and degree of curvature of its turns. We also detected significant differences in the shape of the vestibular system between semi-aquatic and non-aquatic species as well as between the fastest land mammal, the cheetah, and other felid species. These features are related to differences in the species head motion during locomotion.