Inferring the Swimming Mode of Jurassic Plesiosaurs Using Muscle Reconstructions, Bone Histology, and Advanced Finite Element Methods

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After the end-Permian mass extinction, the marine realm quickly recovered, including an adaptive radiation of marine reptiles. One of the most important and long-lasting radiation is the one of the Sauropterygia, of which the Plesiosauria are the most aquatic representatives. The radiation of Plesiosauria occurred in the Jurassic and Cretaceous and lead to a great diversity of taxa but to a low morphological disparity, especially in terms of their extremities. The flippers were transformed to four very similarly-shaped hydrofoils. The locomotor system of plesiosaurs remained practically unchanged for about 135 Ma, implying an optimized energy efficiency for their habitat. Plesiosaurs evolved a unique way of underwater flight in which they employed two pairs of flippers of very similar appearance. Yet, how plesiosaurian underwater flight took place remains unknown due to a lack of fossil and modern analogues. Hence plesiosaur swimming is one of the most challenging phenomena in vertebrate locomotion. We would like to contribute to solving this evolutionary problem by a transdisciplinary set of methods from ingeneering science, paleontology, and biology. First, Caretta caretta, a recent marine turtle will be dissected, measured, and documented for comparison and to gain data that will be used for different finite element methods. The methods include finite element structural analysis (FESA), finite element structural synthesis (FESS), and computational fluid dynamics (CFD). Then plesiosaur flipper muscles will be reconstructed using phylogenetic inference (Extant Phylogenetic Bracket), osteologic correlates, and bone histology. Thorough muscle reconstructions are needed to calculate possible muscle forces with FESA. The results will form the basis for FESS computations to produce finite element syntheses of humeri und femora of Caretta caretta and a plesiosaur. If results of the virtual syntheses match with the fossil finds of plesiosaurs and the preserved specimens of Caretta caretta, muscle reconstructions will be verified. With CFD, possible swimming speeds and the fluid dynamic properties of the plesiosaur flippers will be determined.