Meeting Abstract
Classic studies on shark swimming generalize pectoral fins as rigid hydrofoils that generate lift. However, morphology varies greatly among sharks and this generalization may not embody the function(s) of pectoral fins in all species. Fins are classified into two groups dependent on the extent to which radials support the fin. Skeletal support is hypothesized to vary among species that inhabit different environments; however, little is known about radial morphology. The cross-sectional anatomy and calcification patterns of batoid cephalic lobe and pectoral radials differed significantly among species and corresponded to differences in locomotor style and habitat use. The goal of this study was to examine the cross-sectional morphology of the radial elements of sharks with differing whole-body morphology, locomotor styles, and habitat use. We calculated the second moment of area, a structure’s resistance to bending, at 1cm increments along the fin for three radials: the radial along the leading edge, the longest radial, and the radial supporting the trailing edge. We also measured the cross-sectional area of the whole radial and calcified struts, and calculated the percentage of calcification at each increment. We hypothesized that benthic species have radial elements with the least amount of calcification whereas oceanic species have the highest calcified radials. We also predicted that all species have radials that resist bending in the medial-lateral more so than dorso-ventral bending. We propose that these differences in pectoral fin functional morphology exemplify an evolutionary trade-off where benthic species have flexible pectoral fins that aid in maneuvering rock and reef environments, and oceanic species have stiffer fins that maximize hydrodynamic efficiency for sustained swimming.
