Humans have always been fascinated with the one part of the world that we could not conquer - the sky. How did the earth's first flying creatures come to be? In this episode of Evolve we will examine the first vertebrate flyer, the pterosaur, which took to the air over 220 million years ago and eventually evolved to be the size of small airplanes. Scientists have long pondered how they, the largest flying creatures ever, were able to achieve such an astonishing feat. Scientists examine the fossil record and living birds to try and unlock how some species evolved to have the remarkable trait of flight.