Morphological variation of the conus arteriosus in Chondrichthyes: Implications for ecology and evolution

Cartilaginous fish have diverse morphological traits that are essential for understanding their evolutionary history and ecological adaptations. However, the conus arteriosus and its valves, key components of the heart and blood circulation, have been underexplored in phylogenetic and ecomorphological contexts. Here, we (1) characterize the morphological diversity and distribution of conal valves across Chondrichthyes, (2) evaluate the phylogenetic signal of valve characters and their potential usefulness for understanding evolutionary relationships, and (3) test whether variation in valve morphology is associated with lifestyle and locomotor demands. Our results show that the number of valves, as well as their distribution along the conus arteriosus, is generally consistent with the pattern observed in previous studies of two to seven rows of valves, with predominantly three series. Novel findings include a higher number of valve rows (up to six) than previously found in sharks and the first detailed descriptions for the orders Torpediniformes and Squatiniformes. Our results indicate that conal morphology is weakly correlated with phylogeny, but is strongly associated with locomotor demands and lifestyle.