Tyrannosaurus rex runs again: a theoretical analysis of the hypothesis that full-grown large theropods had a locomotory advantage to hunt in a shallow-water environment

Abstract

Abstract Biomechanical analyses suggest that adult large theropods, such as Tyrannosaurus rex, could not run, and its top speed probably was at most 10 m/s. This probably implied a speed disadvantage of adult T. rex compared with some smaller potential prey. Living predators at a disadvantage owing to speed or manoeuvrability sometimes use the environment or special techniques to minimize those differences. Here, I made a theoretical analysis of the possibility that adult large theropods, such as T. rex, could occasionally pursue prey in water to take advantage of their body size. There are arguments based on scaling laws to support this hypothesis. To give an example, I applied a biomechanical model to estimate the speed in a shallow-water environment of adult T. rex and two smaller dinosaurs, a juvenile Edmontosaurus annectens and Struthiomimus sedens. I conclude that by wading or swimming, the adult T. rex would have been faster than smaller prey in water. I also suggest that in water, adult large theropods, such as T. rex, were able to use a running gait that was probably precluded on land. Finally, I propose a near-shore hunting scenario for adult T. rex and other full-grown large theropods.