MOSASAURS AND THEIR RELATIVE BURST AND CRUISE CAPABILITIES

Mosasaurs are great models for reconstructing the aquatic locomotion of fossil animals because they are often well-preserved with most skeletal elements and soft tissue preservation like skin, cartilage, and impressions showing limb and tail outlines. Mosasaurs were the dominant marine reptiles of the Late Cretaceous and are an important clade for which to reconstruct comprehensive, whole-body functions as they relate to ecology and evolution. Due to their exceptional preservation, reliable reconstructions of mosasaurs can be made. Determining relative burst and cruise performance of mosasaurs that span the mosasaurine and ‘russellosaurine’ sides of mosasaur phylogeny were the goals of this study. Both swimming modes are relevant to mosasaur ecology and their role in their respective food webs, dictating major biological aspects like prey capture, predator evasion, and dispersal. For selected mosasaurs, lateral and dorsal reconstructions and mass estimations were made, and values such as tail beat frequency, surface area, and amplitude were determined in order to determine drag and then total thrust for cruising and bursting. Findings show that the relative thrust of mosasaurs in a drag-based burst are most impacted by the lateral tail excursion amplitude. Platecarpus, a ‘russellosaurine’ and relatively smaller-bodied mosasaur, showed the highest burst potential with an exit velocity that was 4.2 times greater than the stouter-bodied mosasaurine Prognathodon, and approximately 3.4 times that of the mosasaurine Plotosaurus, and Tylosaurus a ‘russellosaurine.’ Of the mosasaurines, Plotosaurus indicated a slightly higher initial burst potential than Prognathodon. These results suggest that smaller, less aquatically specialized mosasaurs relied more on bursting than larger, more cruising specialized mosasaurs. However, all mosasaurs showed potential for high burst speeds, including Plotosaurus, considered the most derived mosasaur and a more pelagic cruiser.