Replica of Pterosaur, meaning "winged lizard". Often referred to as pterodactyls, pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period (220 to 65.5 million years ago). Pterosaurs were the first vertebrates to evolve powered flight. Their wings were formed by a membrane of skin, muscle, and other tissues stretching from the thorax to a dramatically lengthened fourth finger. Pterosaurs are sometimes referred to in the popular media as dinosaurs, but this is incorrect. The term "dinosaur" is properly restricted to a certain group of terrestrial reptiles with a unique upright stance (superorder Dinosauria), and therefore excludes the pterosaurs, as well as the various groups of extinct aquatic reptiles, such as ichthyosaurs, plesiosaurs, and mosasaurs. Royal Tyrrell Museum, Drumheller, Alberta, Canada.