Winged Beasts, a squandered resource?

[Morthoron]

Originally Posted by Lalwendë

This:

means they are probably not reptilian creatures. I can't think of any reptiles which thrive on cold and moonlight. Even British snakes need to bask, and they hibernate in winter, as do Toads and Frogs, so I doubt it's Amphibian either.

If it's a mammal then it's one which doesn't need to be nursed on milk, or else has been weaned early. Being able to fly doesn't rule out it being a mammal of course.

Well, Tolkien was never one for the proper placement of biospheres or ecosystems. If the 'Withered Heath' can best be described as the hatchery or nursery of dragons, then its northern proximity indicates that in Middle-earth reptiles of the draconis order were adaptable to rather frigid climes, or at least wild fluctuations of temperature. With their innate intelligence, they could have been precursors to mammals!

Originally Posted by Lalwendë

Also, they were "lingering in forgotten mountains". Does that literally mean 'in' the mountain, as in a cave? Or does the use of 'eyrie' exclude that?

I think it's yet another example of archaic Tolkienisms. Tolkien says 'in' when he means 'on' or 'atop', and uses 'under' when he means 'in' or 'below'. So lingering 'in' forgotten mountains means existing 'atop' or 'along' the mountain. Or at least, that's my understanding, without getting in too deep.