Comparative morphology of the skeletal labyrinth in extant squalomorph sharks

The inner ear of vertebrates serves dual roles, detecting sound as well as maintaining equilibrium. The increased accessibility of Computed Tomography (CT) provides an opportunity to assess the morphology of the skeletal labyrinth, which houses the membranous labyrinth of the ear, in one of the two primary clades of elasmobranchs: Squalomorphi. This study describes the morphology of the skeletal labyrinth of 10 species of squalomorphs: Chlamydoselachus anguineus, Heptranchias perlo, Hexanchus griseus, Notorynchus cepedianus, Squatina californica, Centrophorus squamosus, Squaliolus laticaudus, Oxynotus centrina, Isistius brasiliensis, and Etmopterus bullisi. Hexanchiformes are found to have more robust skeletal labyrinth spaces housing the semicircular canals and ampullae, while taxa from Order Squaliformes have more slender labyrinths. Given the variety in diet and habitat across this sample of taxa, we advocate for broader taxonomic coverage and finer assessment of ecological categories in the future, as well as quantitative assessments of ear geometry and its relationship with phylogenetic history, locomotion, and habitat.