Thread: Raiths! Raiths on WINGS!
I think they're maybe supposed to be dinosaurs. In ROTK there's a line about them being a "creature of an older world". Although in one of his letters Tolkien says their not necessarily supposed to be a pterodactyl, he does acknolwedge that there's a strong similarity.
Maybe Morgoth in the first age,marred some eagles and those became the " Fell beasts" . Sauron found some in the unknown East and made them more hideous to behold.
In the Sillmarilion, there is a line about Morgoth making beasts "of horn and Ivory" that "died the earth red with blood". Perhaps the fell beasts were created then, but like a number of other animals faded into obscurity (Mumakil). However, when Sauron came to power in the Third Age he was defiantly looking for as many hand-me-downs as possible. After searching long and hard, perhaps he found them lurking in the east or far north. Maybe after the rising of the sun and moon they fled to caves and obscurity, but when Sauron found them he nourished them and they grew to endure the sun. Then they enter the text. This is Largely conjecture, however it is somewhat supported and is logical, so this is a potential answer. Someone who is more knowledge might give a definitive answer. In any case you could tell your friend about this theory.