Meeting Abstract
Weberian apparatus is an evolutionary functional novelty consisting of a series of modified peri-vertebral elements for sound transmission (specialized hearing) in all Otophysi fishes. It is especially well developed in cypriniforms including members of the family Catostomidae. Complementing a rich history of anatomical study into this group, morphology of the Weberian apparatus has recently become available for study in the earliest members of Catostomidae. To explore possible evolutionary trends for this group of fish, I examined the Weberian apparatus in all the oldest catostomids (Eocene in age) and the majority of extant catostomids. The fossil taxa with preserved Weberian apparatus examined for this study include Amyzon aggregatum, A. gosiutense, A. hunanese, A. kinshenehnicum, “Amyzon” brevipinne, and Plesiomyxocyprinus arratiae. The shape and size of Weberian ossicles are similar across phylogeny and geologic ages of catosotmids, whereas other associated elements are highly diversified. Synapomorphies observed from both fossil and extant taxa are: presence of a large transverse plate between the left and right rib 4; rib 2 being fused into rib 4 and together contributing to the transvers plate; and the os suspensorium emerging from rib 4 instead of the centrum. Evolutionary trajectories across Eocene to present materials were most prominent in the length, width, and projecting direction of rib 4, the size of neural spine 4, and shape and size of the neural complex. These trends coincide with taxonomical diversification and geographical dispersal of catostomids, suggesting that Weberian apparatus evolution is associated with both speciation and niche differentiation of catostomids.
