Spinosaurus

One of the most mysterious dinosaurs, the Spinosaurus continues to be a topic of hot debate among paleontologists. We know little about its behavior, whether it was mainly an aquatic creature, or a land creature. In 2008, Nizar Ibrahim discovered tail vertebrae where neural spines were found, indicating that the Spinosaurus had an oar shaped tail, which Ibrahim took as evidence of Spinosaurus's aquatic capabilities. Along with the tail, Ibrahim also discovered bones of the leg, which appeared very small in comparison to the rest of the body. This also indicated that the Spinosaurus was a swimming creature as the short legs would not be very good at supporting the Spinosaurus on land.  However, other researchers modeled its movement underwater and found it to be inefficient, not being able to swim very fast. Despite this finding, the Spinosaurus is still generally considered a semi-aquatic creature.