Plesiosaur Body Shape and its Impact on Hydrodynamic Properties

Despite the variability of cross-sectional body shape within Plesiosauria, its impact on plesiosaur buoyancy and stability has never been investigated. This study focused on Tatenectes, Cryptoclidus, and Muraenosaurus due to their variable body morphologies. Reconstructions were created based on measurements and photographs from fossil remains. The ability of computer models, based upon the reconstructions, to reach equilibrium after submersion, sink via lung deflation, and recover from a lateral roll was tested. For the computer models, Muraenosaurus was replaced with Thalassomedon, which had a similar morphology. Cryptoclidus and Thalassomedon recovered from submersion faster than Tatenectes. All models achieved negative buoyancy with 85-95% lung deflation. Tatenectes and Cryptoclidus recovered from lateral roll quickly, 10 and 12 cycles respectively, compared to Thalassomedon (25 cycles). The findings suggest that dorsoventrally compressed plesiosaurs, such as Tatenectes and Cryptoclidus, inhabited shallow-waters and deep-bodied genera, such as Thalassomedon and Muraenosaurus, inhabited deep-water environments