Pterosaurs

Of all the creatures that ever lived, pterosaurs probably most closely resemble the dragons of European legend. Reptilian and featherless, pterosaurs flew on wings of hide that were supported by a single long and boney finger. The smallest pterosaur was the size of a sparrow, while Quetzalcoatlus -- named after the Aztec god -- had a wingspan of more than 40 feet, making it the largest flying creature ever. Quetzalcoatlus is shown here.

by www.livescience.com