6 - Plesiosaur
No collection of the top 10 extinct animals would be complete without the enigmatic plesiosaur, a large aquatic reptile that swam in the world's oceans during the Jurassic and Cretaceous periods. There are several different species of plesiosaur, but the most famous are the ones with a very long neck topped by a tiny head. Most of these animals were astonishingly large, sometimes reaching a whopping 65 feet in length.
Many people believe strongly in a connection between the plesiosaur and the Loch Ness Monster, a legendary creature that some say inhabits the waters of Loch Ness in Scotland. Indeed, some believe that the appearance of the Loch Ness Monster is evidence of a living plesiosaur. However, according to the fossil record, plesiosaurs disappeared at the end of the Cretaceous Period, about 65 million years ago. And contrary to popular belief, they were not dinosaurs, despite the fact that both groups lived and died off at the same time.