Fire-drakes

Uruloki in Quenya, the fire-breathing kind of dragon, and perhaps a breed apart rather than a stage of growth. They grew to enormous size and threw flame and burning vapour from mouth and nostril, and the heat of their bodies alone could dry a riverbed or melt a road through deep snow. Most of the dragons whose names are remembered were of this kind, though not all of them served Morgoth. The first and most renowned was Glaurung, who came out of Angband in the Elder Days and was a terror to the Elves of Beleriand.