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. Editor's summary: The Otophysan suborder contains nearly 70% of all freshwater fish species, many of which are quite familiar, such as carp, catfish, and eels. It had been believed that this group originated in fresh water before the breakup of Pangea. However, after analyzing a recently discovered Late Cretaceous fossil, Liu et al. concluded that this group first evolved in a marine environment and later colonized fresh water multiple separate times. Furthermore, the fossil informs on the evolution of the group's Weberian hearing apparatus, suggesting that it was associated with freshwater adaptations. —Sacha Vignieri [ABSTRACT FROM AUTHOR]