Gliding through the air, wyverns wheel and bank their way across the Melidoran skies. These flying vertebrates have managed to colonize every corner of the globe, from the frigid polar regions to tropical forests and dry deserts. Some species even spend their entire lives flying over the great oceans.

Wyverns are not endognathans — they are instead members of a sister group called Monognatha. They lack inner jaws, and the upper two mandibles on their outer jaw have fused together, creating a simple two-part jaw. Additionally, like all monognathans, they have lost their front two limbs. Their four limbs are connected together by a membrane of skin, making them resemble a Terran pterosaur. Limb loss has occurred many times among Melidoran land vertebrates, and is not unusual — consider how Terran snakes evolved from four-legged ancestors.

The Common Rosin is a cosmopolitan species, found on practically every continent. It is about the size of a Eurasian Blackbird, and like its Terran counterpart it is quite a generalist eater. Anything goes, from tenucaulian spores to small trilomorphs (radially symmetrical insect-like creatures).

Some wyverns have become highly specialized. Brinelappers are found in the highland deserts of the Avalonian Plateau. Here, the only sources of water are hypersaline lakes. Any normal creature would die of salt poisoning if they attempted to drink the water here. But Brinelappers have a special technique. As they ingest the water, they force it through a series of high-pressure tubes in their esophagus. As this happens, the water moves from the region of high salt concentration in the tubes to the surrounding region of low salt concentration. The Brinelapper then drinks the freshwater that pools on the membranes of its esophagus. In effect, this process is a biological form of reverse osmosis.

Perhaps the most spectacular of all the wyverns is the Spitfire of the Notian Highlands. Like the fire-breathing dragons of Terran mythology, Spitfires are capable of producing a powerful flame. This flame is created when methane gas, travelling up from the Spitfire's digestive system, reaches the outer jaw. A special arch-like organ, located on the upper mandible, acts like a piezoelectric igniter by generating an electric spark when squeezed. The resulting spark ignites the gas, which burns brilliantly in the high-oxygen atmosphere. Spitfires have a nasty habit of swooping down towards unfortunate mountain creatures that forage near the edge of cliffs. The started creature, burned by the heat of the flame, tumbles down the cliff to its death. Once dispatched, the Spitfire glides down and feeds on the charred carcass.