Marine origins and freshwater radiations of the otophysan fishes

Otophysans, known for their enhanced hearing enabled by the complex Weberian apparatus, comprise two-thirds of extant freshwater fish species. Previously, they were thought to have originated in fresh water before the breakup of Pangea, implying a nearly 80-million-year gap between the origin and oldest known fossil. However, the discovery of a Late Cretaceous freshwater otophysan challenges this view. Integrating fossil, morphological, and genomic data, we estimate a younger crown group origin of ~154 million years ago. Notably, ancestral range and habitat reconstructions indicate marine origins for the otophysan crown groups, with at least two transitions to fresh water. Functional simulations of the Weberian ossicles of this fossil suggest that the distinctive hearing capabilities of otophysans evolved in conjunction with fusion of hearing ossicle parts and freshwater adaptations.