While the wyvern, or at least the living beast now known by the name, is not native to Aren, there is reason to describe it here. Its story starts in middle Ordosia, in the kingdom of Felangia whose notable chalk deposits were mined for at least a millennium before the Imperial times. The Thelquamian scholar Evann the younger wrote a treatise on geology, "On minerals", where he mentions that among the bones of goblins, kobolds and bears, the miners often find bones of the "whiddwerm". Evann describes the creature as a serpentine animal with a long tail and neck, membraneous wings, one pair of somewhat birdlike legs and long jaws lined with sharp teeth. The name of the creature came from the old Galanic words "whidd" which means both white and chalk, and "werm", meaning serpent. What Evann was in fact describing was a common fossil in Felangian chalk: the well preserved remains of an ancient flying animal that had become extinct tens of millions of years ago.
Since dragons were known to nest in caves, it was assumed that the whiddwerm, which was soon shortened to widvern in the mouths of Velaneics, was a two-legged dragon of some sort, and it was described accordingly in bestiaries. These early mentions often attribute the widvern with a breath that causes lung disease, which many miners were indeed suffering from, although not because of any mysterious draconic creature dwelling underground.
It appears that scholars were beginning to realize that there was no truth to the existance of a living wyvern, because it was given certain impossible properties, such as wyvern venom being able to resurrect the dead and its skin having the property of being able to turn lesser metals into gold. It is however also possible that these originated from miners' legends and were diligently written down by scholars who didn't know better.
The latter indeed seems more likely, considering that the notable mage Cordastros of Savaria, who had studied the lesser of the Gates of Five, learning how to summon matter from different parts of Aren and beyond, decided to summon and capture the fabulous wyvern to gain its powers. He finally succeeded in his quest at an old age, locating and summoning a creature fitting the descriptions and illustrations from notable bestiaries. This, however, was not an Arenian creature, but a large predator from the same world from which dragons had originally come, known sometimes by the name Ziruvach.
The wyvern proved to be more than the old mage could handle, and although he survived its initial attack, the beast escaped. Terror struck the countryside surrounding the city of Savaria as the wyvern, assumed by many to be the dreaded cockatrice, attacked several farms and lone travelers. Apparently trying to find prey it would recognize as edible, it often merely ate the internal organs, sometimes even left its victim dead without taking a single bite.
A notable feature in the attacks was that the wyvern would always attack from the air, grasping the person or beast with its talons and then driving a long spike at the end of its tail into the flesh. Most victims of the beast, no matter how badly mauled, had the signs of severe poisoning. Eventually tracked down and killed by the city guard, helped by the advice of Cordastros himself, the dead wyvern was taken back to the city, where everyone could see the dead beast, and witness for themselves that it hadn't been a cockatrice, a notion that had caused widespread panic.
From the city records we know the wyvern of Savaria had a roughly man-sized green white-bellied scaly body with long taloned legs, dragon-like wings supported by three elongated fingers, an arching neck ending in a slender dragon-like head adorned with two rows of horny spikes behind the eyes. A row of quills ran down its neck and back, ending at the base of the tail. The long tail of the animal flexed only downwards (or at least had very limited sidewise movement) and ended in a diamond-shaped fin followed by a sharp hollow "fang-like" spike, which the animal used to deliver its poison into its victims. The text also mentions two curved spikes protruding from the chest.
Sadly the body of the wyvern was burned after it started to rot and "caused a horrid stench", and not even a part of it was saved for later study. Cordastros himself died of the injuries he had sustained before seing the animal again, and other mages and alchemists were probably too afraid to ask for parts of the animal, fearing that they would be associated with the wyvern attacks.
The fact that the wyvern of Savaria had lacked all the magical qualities associated with wyverns in bestiaries caused scholars to widely abandon them from the descriptions, although the claim that silver turns into gold if polished with wyvern skin survived for long. The deadly tail spike, on the other hand, was added to all of these later descriptions.
It wasn't until two centuries later, during the age of the United Empire, that Cordastros' success at summoning a wyvern was replicated. The animal summoned by several Imperial master mages was succesfully captured and brought into the Imperial Menagerie. The animal appears to have been of a different species from the wyvern of Savaria, as it was considerably smaller, had an olive skin with black stripes, a pale yellowy belly and a red neck wattle, while lacking the horny cranial growths of the Savarian beast. It also had rudimentary arms with two claws protruding from its chest. This was later understood as a feature that linked wyverns to the hexapodal dragons.
The wyverns summoned by Imperial mages have provided some clues to dragon evolution. It appears that wyverns diverged early from the dragon lineage, before they became sensitive to magic. The wyvern lacks any ability to use magic and its intelligence is, at best, at the level of a bird of prey. It has given up its first limb pair in exchange for more powerful flight muscles, and probably to shed excess weight.
Like dragons, wyverns have hollow, extremely strong bones, and a similiar wing structure with the thick wing membrane attaching to the pelvis, but they have all but lost the first and second finger in their wings, which do not support the main wing membrane. Based on the slender snouts of wyverns summoned, it appears that they kill their prey with the fast-acting venom delivered with the tail stinger. Short-tailed wyverns without a stinger have also been summoned, but based on their enormous wingspan and narrow jaws lined with sharp slender teeth, they appear to be completely piscivorous gliders.