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.
Some parallel worlds have different time-flows, like the fabled dwelling-places of the elves: those who visit them under the hill for a night return to find that years have passed in this world. Perhaps it is the gate leading between the worlds which causes the alteration. If a gate were 'misaligned', the shift from '| |' to '| \' or '| /' as it were would lead to that difference, much as a light-beam split and bent by a prism ends up taking a longer path. There might even be a mathematical function linking degree of misalignment to alteration of time-rate.