The fossils remain of the first flying vertebrates, the pterosaurs; have intrigued archaeologists for more than two centuries. How such large creatures, which weighed in some cases as much as a piloted hang glider and had wingspans from 8 to 12 meters, solved the problems of powered flight, and exactly what these creatures were, reptiles or birds are among the questions researcher have puzzled over. Perhaps the least controversial belief about the pterosaurs is that they were reptiles. Their skulls and hind feet are reptilian. The structure of their wings suggests that they did not evolve into the class of birds. In pterosaurs, a greatly extended fourth finger of each forelimb supported a wing-like membrane. The other fingers were short and reptilian with sharp claws, in birds, the second finger is the principle strut of the wing, which consists primarily of feature & lithe pterosaur walked or remained stilt the fourth finger, and with it, the wing could only turn upward in an extended inverted V-shape alongside the animal's body. The pterosaurs looked like both birds and bats in their overall structure and proportions. This is not surprising because the design of any flying vertebrate is subject to aerodynamic constraints. Both the pterosaurs and the birds have hollow bones, a feature that represents a saving in weight. In the birds, these bones are reinforced more massively by internal struts. Although scales typically cover reptiles, the pterosaurs probably had hairy coats.