Why did many pterosaurs have large crests on their heads?

With a wingspan of 6 to 10 feet, the pterosaur also had two long, thin bones sticking out of its head, probably connected by soft tissue, forming a large crest. ... Scientists have many theories about why crests evolved, which include recognizing one's own species, cooling, or even steering through the air. read more

From the BBC: Flying reptile mystery 'solved' UK scientists say they have solved the mystery of why prehistoric flying reptiles grew crests on their heads. read more

The pterosaurs are divided into two groups; the Rhamphorhynchoids had no crests and tails, while the Pterodactyloids had crests but no tails. Most large Pterodactyloids had crests on their head, possibly colored brightly, but different types of Pterodactyloids had differently shaped crests. read more