Meeting Abstract
Morphological variation is substantial across the 8 orders of living sharks (selachimorph elasmobranchs), with body shape and fin shape predicted to be strongly associated with feeding ecology and locomotor behavioral patterns throughout the shark phylogeny. The goal of this study was to explore the evolution of fin and body shape across a shark phylogeny using geometric morphometric analysis to further understand the phylogenetic patterns of body shape and fin shape among shark species. How has the asymmetrical caudal fin evolved across shark species? It is predicted that fast swimming or high endurance pelagic sharks will have high aspect ratio tails, with greater dorsoventral symmetry to facilitate efficient locomotion. How have dorsal fin shape and positioning evolved across elasmobranchs? We predicted that the relative positions of the two dorsal fins and the presence or absence of the second dorsal fin is associated with body length and shape due to constraints posed by locomotor hydrodynamic principles. We pruned an existing phylogenetic time tree of Chondrichthyes (Stein et al. 2018) to include 225 shark species representing 7 of the 8 extant shark orders, with at least one species per genus. Body shape, fin shape, and fin position of these 225 species were analyzed using geometric morphometric analysis of 108 landmarks, with detailed shapes generated for each fin. Morphometric analysis revealed high variation in dorsal and caudal fin shapes and significant correlation between them, suggesting covariation of fin shapes is driven by hydrodynamic constraints. We conclude that patterns of body and fin shape, including caudal aspect ratio and asymmetry, are strongly associated with locomotor mode, and that fin shapes have undergone multiple patterns of morphometric convergence across shark evolution. NSF DEB 1541547
