Scientists report finding tracks from a fossil lake-bed which exhibits marks left behind by a dinosaur's toes as the animal floated through shallow water. Though it's not too surprising (most groups of land animals can swim to some degree) this is the first solid evidence that suggests dinosaurs had the ability to swim.
The small dinosaur who left the tracks was a theropod—the group of meat-eating dinosaurs that includes T. rex. So while 50-foot-long sharks were a good reason not to go swimming in prehistoric seas, this new finding suggests T. rex might be of bigger concern to a time-traveling scuba-diver. Dinosaurs, however, went extinct before the gigantic sharks evolved, so a mega-shark vs. T. rex water battle can only happen in our imagination—or perhaps the movies.