Tail-propelled aquatic locomotion in a theropod dinosaur.

In recent decades, intensive research on non-avian dinosaurs has strongly suggested that these animals were restricted to terrestrial environments. Historical proposals that some groups, such as sauropods and hadrosaurs, lived in aquatic environments were abandoned decades ago. It has recently been argued that at least some of the spinosaurids-an unusual group of large-bodied theropods of the Cretaceous era-were semi-aquatic, but this idea has been challenged on anatomical, biomechanical and taphonomic grounds, and remains controversial.