Meeting Abstract
Multiple independent land-to-sea transitions in extinct reptiles led to a great diversity of secondarily marine reptiles during the Mesozoic. Ichthyosaurs, as well as members of the mosasauridae and thalattosuchian crocodylomorphs, relied on axial undulation and converged on a bi-lobate caudal fin morphology. While these tails are superficially similar to shark caudal fins, the vertebral column supported the ventral lobe of the tail. It has been proposed that this may have been to counteract the buoyancy of the reptiles’ lungs or may have helped make the animals more manoeuvrable when diving. Coupled with the question of tail morphology are changes in body and tail flexibility. It has been hypothesized that as these lineages adapted to more obligate marine lifestyles there was an increase in overall body stiffness, which would have led to more efficient locomotion. In ichthyosaurs, body stiffness has been estimated based on vertebral morphology, but this does not address stiffness conferred by soft tissues or muscle activation, and this only addresses the stiffness of the ventral lobe. Our goal is to understand how skeletal and soft tissues affect tail stiffness in both lobes and how this relates to fluid dynamics. Using sharks as an extant analogue, as well as 3D printed models, we are comparing tail flexibility and morphology to better understand the natural history of these long extinct marine reptiles. Shark tail flexibility varies between species, as do skeletal and soft tissue morphologies, but for all species the dorsal lobes are more passively flexible than the unsupported ventral lobes. Understanding the relationship between tail morphology, stiffness, and fluid dynamics will help us better explain the convergent evolution of extinct marine reptile tails and their function.
