Flume study of simulated feeding and hydrodynamics of a Paleozoic stalked crinoid

Abstract

Life-sized scale models and a flume were used to observe simulated feeding and hydrodynamics of the Paleozoic camerate crinoid, Pterotocrinus. Three orientations of the crown and filtration fan (downcurrent, upcurrent, upright) in a gentle (3.5 cm/sec) current were used. Maximum baffling of the current and eddying of water into feeding areas occurred where models were oriented like most living stalked crinoids, with a parabolic filtration fan perpendicular to the current and ambulacral side downcurrent. Facing the ambulacral side of the fan upcurrent reduced time available for entrapment of potential food particles. Calyx shape was important in modifying the nature of the filtration fan baffle. Overlapping (36%) of the pinnulate arms increased the baffling effect of the filtration fan. Conspicuous tegminal structures, the Pterotocrinus wing plates, only had a baffling effect where the fan was in an upright position or the arms were infolded between the wing plates. Species of Pterotocrinus possessing blade-like wing plates could have fed effectively in several different orientations. Evolutionary success of Pterotocrinus species with blade-like wing plates probably resulted from dual feeding and protective functions of the wing plates.