For a long time people thought pterosaurs could only glide and soar, and were not strong enough to flap their wings. In the 20th century, after aeroplanes had been invented, our understanding of flight advanced. English palaeontologists showed that pterosaurs could fly, and Tilly Edinger showed that by the end of the Jurassic, pterosaur brains were more like that of modern birds than of "Archaeopteryx". Recent work has used working model to simulate their flight. The wing membrane was about 1mm thick, with a tough skin and had long fibres reinforcing it. This can be clearly seen in some of the fossils. The structure helped the wings survive the stresses of flight. The larger pterosaurs were mainly soarers, as is the case with birds today.