large. The smallest species had a wingspan no less than . The most sizeable forms represent the largest known animals ever to fly, with wingspans of up to . Standing, such giants could reach the height of a modern giraffe. Traditionally, it was assumed that pterosaurs were extremely light relative to their size. Later, it was understood that this would imply unrealistically low densities of their soft tissues. Some modern estimates therefore extrapolate a weight of up to for the largest species. Skull, teeth, and crests Compared to the other vertebrate flying groups, the birds and bats, pterosaur skulls were typically quite large. Most pterosaur skulls had elongated jaws. Their skull bones tend to be fused in adult individuals. Early pterosaurs often had heterodont teeth, varying in build, and some still had teeth in the palate. In later groups the teeth mostly became conical. Front teeth were often longer, forming a "prey grab" in transversely expanded jaw tips, but size and position were very variable among species. With the derived Pterodactyloidea, the skulls became even more elongated, sometimes surpassing the combined neck and torso in length. This was caused by a stretching and fusion of the front snout bone, the premaxilla, with the upper jaw bone, the maxilla. Unlike most archosaurs, the nasal and antorbital openings of pterodactyloid pterosaurs merged into a single large opening, called the nasoantorbital fenestra. This feature likely evolved to lighten the skull for flight. In contrast, the bones behind the eye socket contracted and rotated, strongly inclining the rear skull and bringing the jaw joint forward. The braincase was relatively large for reptiles. In some cases, fossilized keratinous beak tissue has been preserved, though in toothed forms, the beak is small and restricted to the jaw tips and does not involve the teeth. Some advanced beaked forms were toothless, such as the Pteranodontidae and Azhdarchidae, and had larger, more extensive, and more bird-like beaks. Some groups had specialised tooth forms. The Istiodactylidae had recurved teeth for eating meat. Ctenochasmatidae used combs of numerous needle-like teeth for filter feeding; Pterodaustro could have over a thousand bristle-like teeth. Dsungaripteridae covered their teeth with jawbone tissue for a crushing function. If teeth were present, they were placed in separate tooth sockets. Replacement teeth were generated behind, not below, the older teeth. The public image of pterosaurs is defined by their elaborate head crests. This was influenced by the