200 million years ago, the first vertebrates took to the air. Some paleontologists thought that since pterosaurs had reptilian characteristics, they must have been cold-blooded, slow-moving, and poor flyers. We know now that they were warm-blooded, active creatures, with powerful flight muscles. Pterosaurs had large eyes, as birds do, suggesting they had sharp vision and were active by day. Some were probably bipedal, walking on their hind legs like birds, and of course they had hollow bones just as birds do. Pterosaurs did not have feathers. Instead, they had fur to keep warm and papery wing membranes for flight.

There were two major groups. Rhamphorynch pterosaurs, with teeth and long tails, dominated skies of the Jurassic period. They gave rise to pterodactyls, which had short tails and, in many cases, toothless beaks. Quetzalcoatlus northropi was the largest known pterosaur. Its wings spanned perhaps 11 meters, and it weighed about 65 kilograms. Pterosaurs had a wide range of feeding adaptations and held similar niches to the birds of today. Competition with birds may have contributed to their late-Cretaceous extinction.