3D PRINTING PECTORAL FINS ATTACHED TO BACK OF THE SKULL IN EXTINCT CARTILAGINOUS FISHES (INIOPTERYGIANS) TO UNDERSTAND FUNCTION

Most fishes today have paired pectoral fins attached laterally or ventrally to their shoulder girdles, which they use to generate thrust or lift in swimming. Iniopterygians, an order of marine Late Carboniferous cartilaginous fishes from North America, had an array of pectoral fin forms located at the nape and sometimes attached to the skull. This placement is not observed among the 34000 species of living fishes and little is known how such unique paired fin position affects locomotion. Previous studies conducted on living fishes (labriforms and salmonids) with laterally attached pectoral fins have demonstrated a relationship between locomotion and fin aspect ratio, a metric combining fin span and area. High aspect ratio fins are long and narrow proximodistally and associated with faster speeds and greater lift, while low aspect ratio fins are short and stubby and more likely to be used for maneuvering. We will experimentally test whether the same properties apply to the diverse, dorsally-positioned pectoral fins of Iniopterygians. We hypothesize that both the low and high aspect ratio fins located at the nape are likely to induce greater lift than those located more ventrally, based off Bernoulli’s principle, and thus diversity in form likely results from additional functionality. We will use 3D Computer-Aided Design software and 3D printing to create physical models of five Iniopterygian taxa. These will be placed in a water flume with the fins fully abducted and the body mounted to prevent pitching. To sum the magnitude of lift and drag forces acting on the model, digital particle image velocimetry will be used, as is standard for similar tests of living fishes. This study represents the first experimental test of fin function in these extinct fishes, and the first to use 3D printed models of fossil bodies.