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Comparative morphology of shark pectoral fins

Citation

Hoffmann, Sarah; Buser, Thaddaeus; Porter, Marianne (2020), Comparative morphology of shark pectoral fins, Dryad, Dataset, https://doi.org/10.5061/dryad.j3tx95x9b

Abstract

Sharks vary greatly in morphology, physiology, and ecology. Differences in whole body shape, swimming style, and physiological parameters have previously been linked to varied habitat uses. Along with whole body morphology, shark pectoral fins are also previously described to vary in both shape and skeleton; however, there are limited comparative data on external and skeletal morphology. Further, fins were previously categorized into two discrete groups based on the amount of skeletal support present: (1) aplesodic, where less than half of the fin is supported and (2) plesodic where greater than half of the fin is supported. These discrete classifications have been used to phylogenetically place species, though the methodology of classification is infrequently described, and the comparisons may not be valid. Additionally, our understanding of shark pectoral fin ecomorphology is limited by access to samples from a broad variety of species. In this study, we sampled fins from various families, orders, and ecological classifications. We examined the external morphology, skeletal extent, and cross-sectional shape of the cartilaginous elements. Using phylogenetic comparative methods, we show that fin morphology does not differ significantly when considering the level of relatedness between species, suggesting there may be some mechanical constraint. We also describe a range of skeletal extent, rather than two discrete categories. We find that fins are shaped like hydrofoils in cross-section, supporting hypotheses that fins may be lift producing structures in sharks. Finally, we find that a number of morphological variables such as number of radials, radial calcification and shape, and fin taper all correlate with skeletal extent. Within these morphospaces, we also describe that some orders/families tend to occupy certain areas with limited overlap. With this study, we demonstrate that there is some mechanical constraint limiting variations in shark pectoral fin morphology, but there are subtle differences that appear to occur within shark groups that share close phylogenetic relationships and similar biological parameters.