When naturalists first began studying pterosaur fossils at the turn of the 19th century, they had the same reaction you probably would: What IS that? They didn't really have anything to compare the bones to, and as a result, misguided theories began flying faster than a pterosaur with a tailwind. But this is science. New discoveries soon led to new knowledge, and today paleontologists know much more about pterosaurs' place in evolutionary history.
It's not too surprising that scientists initially tried to connect pterosaurs to modern birds and bats, given their shared ability to fly. Anatomy and surgery professor Samuel Thomas von Sommering first suggested that the creatures were some type of bat in the early 1800s, a theory that was only bolstered by some pretty great drawings of furry pterosaurs with big ears. Paleontologist Harry Seeley made a similar goof in his 1901 book, "Dragons of the Sky," in which he insisted birds were the descendants of pterosaurs [source: Unwin].
While there are a lot of reasons these two men were wrong, the most basic explanation has to do with the wings. On both bats and pterosaurs, the wings are made from a membrane stretched between their arms and legs. However, the outer part of this wing is supported by four fingers in bats and just one finger in pterosaurs. Bird wings are mostly supported by their arms and are obviously covered in feathers [sources: Unwin, Hutchinson].
What's less clear is what came before pterosaurs. Cuvier, the French naturalist, took a step in the right direction when he suggested in the early 1800s that pterosaurs were reptiles (although that theory didn't gain full acceptance for another century). Since then, paleontologists have been working their chisels dull trying to place them on the reptile family tree. The problem is that no one has found a protopterosaur — basically a transition fossil between pterosaurs and their lizardlike ancestors. But that hasn't stopped paleontologists from guessing. Of the four main theories that explain pterosaur ancestry, the one that seems to have gained the most acceptance places them in Ornithodira, sort of a sister group to the dinosaurs [sources: Unwin, Witton].