Pterosaurs

Pterosaurs were flying reptiles — close cousins of the dinosaurs, but a separate branch entirely. They appear in the fossil record around 228 million years ago already fully capable of flight, which means the crucial transition happened earlier, in animals we have not yet found. By the time the curtain rises, they are airborne.

Their defining feature is the wing, and it is unlike anything alive today. Where a bird spreads its wing across an entire arm and hand, and a bat stretches skin between four long fingers, a pterosaur built its entire wing on a single, monstrously elongated fourth finger. From the tip of that finger a tough membrane — the patagium — ran back to the ankle, laced with fibres that let the animal change the wing's shape and stiffness in flight.

Built to be light

Flight is a war against weight, and pterosaurs fought it everywhere. Their bones were hollow and walled with struts, inflated by extensions of the lungs — a system of air sacs that also helped them breathe. Some giant species had skeletons that weighed only a fraction of what their size suggests. Many were covered in pycnofibres, hair-like filaments that insulated the body and tell us these were active, warm-running animals, not sluggish reptiles.

Two broad grades: the early, long-tailed "rhamphorhynchoids" of the Triassic and Jurassic, and the later, short-tailed, often spectacularly crested pterodactyloids that dominated the Cretaceous.

Crests, crests, crests

Many pterosaurs wore elaborate head crests — bony blades, soft-tissue sails, even antler-like prongs. Most were almost certainly display structures: billboards for attracting mates and signalling species, the Mesozoic equivalent of a peacock's tail. A few may have helped with steering or temperature, but show was the main business.

From insects to giants

The group spanned an astonishing range. The smallest were the size of small birds, snapping insects out of the dusk. The largest — the azhdarchids like Quetzalcoatlus — stood as tall as a giraffe with wings spanning eleven metres, and likely stalked the ground like enormous storks, plucking up prey the size of a dog.