Pterosaurs (Greek: "winged lizard"), sometimes called pterodactyls ("winged finger") were flying reptiles that lived from the end of the Triassic Period to the end of the Cretaceous period. Pterosaurs were members of the order Pterosauria. They were the first vertebrates to evolve powered flight, after insects about 120 million years earlier.
They are are sometimes called dinosaurs, pterosaurs are not members of superorder Dinosauria and are thus not true dinosaurs, though they did live at the time that dinosaurs dominated terrestrial ecosystems. Pterosaurs lived for a relatively long time (163 million years) for an order of animals, a testament to their domination of the aerial niche. Pterosaurs would have occupied a niche similar to today's birds, but some (including some of the largest) had adaptations to walking on land with all fours, with various species using either sprawling or erect postures. Though sometimes depicted as unsteady on land, some pterosaurs would have been competent runners and walkers, capable of hunting down prey without even taking off.
Although pterosaurs were reptiles, they lacked scales, had a fine layer of hair, were covered in a large stretchy membrane, and were warm-blooded. The Mesozoic was a time when reptiles had diversified to occupy a large number of niches left unoccupied by the class today. Pterosaurs were characterized by long, thin skulls and an enlarged brain to handle the complexity of flight. The fragile nature of pterosaur skulls makes study of them difficult.
Pterosaurs ranged wildly in size, from the 10 in (23 cm) Nemicolopterus to the 39 ft (12 m) wingspan monster Hatzegopteryx, the largest flying animal known, with a 10 ft (3 m) skull, among the largest of any land animal. On several occasions it has been thought that the largest known pterosaur skeleton found at the time represented the largest physically possible flying animal, but a larger specimen has always been found thus far. Even larger specimens may be hidden in some remote area of Mesozoic strata.