Meeting Abstract
The arthropod Anomalocaris canadensis, described from the 508 million-year-old Burgess Shale site, is considered the apex predator of the Cambrian period with its prominent compound eyes, grasping appendages, and circular mouth with serrated teeth. The lateral lobes along its dorso-ventrally flattened body have traditionally been attributed to undulatory propulsion although the role of its unusual fan-like tail remains poorly understood. Swimming efficiency and manoeuvrability deduced from hydrodynamic analysis may provide information about predatory habits and how swimming mechanisms have evolved over time. The current study involves analysis of a three-vane model designed to mimic the tail fin to estimate the likely modes of locomotion. Through direct force measurements and stereoscopic particle image velocimetry, it was found that the geometry exhibited a region of steady-state lift and drag enhancement at angles of attack greater than 25° when compared to an equivalent delta-wing plate. These shapes showed little difference during acceleration from rest; however, at an angle of attack of 30° the lift and drag on the multi-vane model were 15.3% and 17.0% higher than the delta-wing model, respectively. It was found that the secondary and tertiary vanes of the tail-fin abstraction encourage the formation of additional leading-edge vortices, similar to those frequently seen on natural propulsors. The formation of these leading-edge vortices is confirmed by the increase in streamwise circulation measured near the additional leading edges along the length of the chord. The results of the current study suggest that the enhanced resultant normal force on the tail fin of Anomalocaris made it well-suited for manoeuvres, giving it the ability to turn quickly through small radii of curvature.
