Development of the dorsal and anal fin in Kneria stappersii (Otomorpha: Gonorynchiformes)

The order Gonorynchiformes was repeatedly studied to gain new insights into the evolution of its sister-taxon, the Otophysi, the most successful freshwater fish taxon worldwide. Previous ontogenetic studies of gonorynchiforms mainly focused on the anterior vertebral column to investigate the evolutionary origin of the Weberian apparatus. Herein, we highlight the ontogeny of a different skeletal complex, the dorsal and anal fins. We studied the development of the skeletal elements of both fins in the gonorynchiform Kneria stappersii. We gained new insights into the developmental and formation patterns of K. stappersii. We discuss these patterns as well as the development of certain elements like the fin stay in comparison to other gonorynchiforms and available otomorph data. In general, the fin development in K. stappersii is very similar to that of other gonorynchiforms and even otomorphs. Specific differences, however, reveal that much remains unknown about the evolution of median fin elements such as the fin stay.