Don Henderson

Academic paper

Lethaia

39

227-244

Three�dimensional mathematical/computational models of three types of plesiosaur (Liopleurodon � short neck, Cryptoclidus � medium neck, and Thalassomedon � long neck) were used to investigate aspects of their flotation and stability. Equivalent models of an extant alligator (Alligator mississippiensis) and leatherback sea turtle (Dermochelys coriacea) were used as tests. With full lungs, and uniform tissue densities of 1,050 g/l, all five models would float at the surface, with the alligator and sea turtle models replicating the depths of immersion and inclinations observed in living forms. Impractically large amounts of gastroliths were needed to initiate sinking � even with the lungs 50% inflated,10 kg of stones were still required in a 218 kg Cryptoclidus to produce negative buoyancy, and the hypothesis that gastroliths were for control of buoyancy is rejected. However, gastroliths equal to 1% of body weight in the Thalassomedon model were effective at damping out buoyant oscillations of the neck when at the surface and minimizing instability when fully immersed at 10 meters depth. The oblate bodies of Cryptoclidus and Liopleurodon provided effective passive mechanisms for righting the body if perturbed by waves at the surface, but the almost circular cross�section of the Thalassomedon body was ineffective in self-righting. The relatively longer flippers of Thalassomedon may have provided higher drag to resist rolling. The idea that plesiosaurs could maintain their necks above the water surface in an erect manner is rejected due to unbalanced buoyancy torques acting on the body. I] Biomechanics, buoyancy, gastroliths, Plesiosaurs, stability.

English