Board Thread:Suggestions forum/@comment-25987328-20160402234405/@comment-26172435-20160403191336

Just a general note on flying rideable mobs: It takes a huge airborne animal to carry other creatures with the typical weight of a sapient species, or 'humanoid'. Such creatures didn't exist on earth as far as we know. In the world of Tolkien these were huge eagles and dragon-like species, and possibly some oversized swans.

It's wisest to stick to lore-based bestiary elements only for such rare and extraordinary creatures.

Simple additional reasoning: If Tolkien would have conceived the idea of such beasts, he probably would have mentioned them in some lost tale of Numenorean explorer adventures or they would have appeared in some poem or tale as part of his rich legacy.