Hi! (and Fell Beasts...)

[Lalwendë]

Welcome Dwimmerlaik!

That's a good question. Maybe Fell Beasts are a strange hybrid of other creatures. Certainly, there were Dragons, and Sauron knew of bats, and the description of Fell Beasts has elements of both. The wings are like bats' wings, with webbing between 'horned fingers', but the neck is more Dragon-like - there were Dragons without wings, so it is quite possible that Sauron had indulged some of his 'talents' in either creating or breeding these creatures.

I like that phrase:

lingering in forgotten mountains cold beneath the Moon