It's been said that the pterosaur, which can only be described as a bird-reptile-dinosaur-esque-thing, was the largest flying animal. This giant beast -- which roamed the Earth during the Cretaceous period roughly 66.5 million years ago -- was a reptile but not actually a dinosaur. Despite being winged, it wasn't bird, either. The pterosaur basically looked like a platypus on bath salts.