S9-1.2 Jan. 6 Cranial design and feeding mechanisms of batoid fishes DEAN, M.N.*; SUMMERS, A.P.; Univ. of California Irvine; Univ. of California Irvine email@example.com
The two major groups of elasmobranch fishes likely diverged from a cartilaginous and suction-feeding common ancestor, yet underwent a drastic evolutionary divergence in body form. While sharks are largely fusiform, rays and their relatives, even those secondarily evolved to a pelagic lifestyle, are dorsoventrally flattened. This limited morphospace apparently exerted no limitation on feeding niche: batoids have near complete overlap with the myriad feeding modes exhibited by sharks, ranging from dietary specializations (e.g., anguilliform prey, hard prey), to piscivory to filter feeding on a giant scale. Since the batoids are so close to two-dimensional we have examined the evolutionary trajectory of skeletal element associated with feeding in dorsoventral projection radiographs. In a few cases we check the validity of the 2-D assumption with 3-D imaging. There is considerable musculoskeletal diversity in the batoid clade, and using phylogenetic independent contrasts we find that variation lies mostly in length, width and angular variation in the elements of the first two visceral arches (particularly the paired hyomandibulae) and variation in the joints between them. Functional diversity also arose by elaboration and decoupling of the ventral muscles associated with these arches and the pharynx, resulting in a dexterous feeding mechanism capable of hydrodynamic prey manipulation. Musculoskeletal trophic morphology can exhibit impressive diversification despite gross-scale architectural limits imposed by the environment or phylogenetic history.