The authors of Mediaeval bestiaries were not merely concerned with providing a description of creatures. No, for them, everything in Creation had a purpose - nothing had been made without an ulterior aim: the edification and instruction of sinful man. So, each creature described is not merely an animal but a living parable, imbued with moral or religious symbolism.
When the great ice-sheets covered the north, life retreated before them, but some species stayed and endured. Whilst man huddled around fires in his caves, mighty beasts roamed the tundra: the Woolly Mammoth, the Woolly Rhinoceros…and the Woolly Wyvern.
Small red flower, originally sprouted from the blood where St. Senren fell but now found widely over all Laurentia. Occasionally, a rare white flower will be found, with powerful magic properties. It is particularly prized by the religious order, the Senrenites.
A secret MLM (pyramid) company that offers eternal life, but in fact it transfers the life forces of its members to those position "above". If you get high enough, (meaning you get enough new members) you start to enjoy the benefits. Maybe a willing sacrifice is much more effective for the transfer. But no one says, that a suddenly unwilling member, threatening to tell the authorities, may not loose it involuntarily... thus start people to vanish, and aged corpses are deposited somewhere safe.