Board Thread:Fun and Games/@comment-33719810-20171122020843/@comment-26149161-20171206040302

Tolkien comments on this in a fan letter (Letter 211).

Did the Witch-king ride a pterodactyl at the Siege of Gondor?

"Pterodactyl. Yes and no. I did not intend the steed of the Witch-King to be what is now called a 'pterodactyl', and often is drawn (with rather less shadowy evidence than lies behind many monsters of the new and fascinating semi-scientific mythology of the 'Prehistoric'). But obviously it is pterodactylic and owes much to the new mythology, and its description even provides a sort of way in which it could be a last survivor of older geological eras."

Ithilion, Discussions Moderator (Auta i lómë)