: Glaurung (sp?), if he actually was a Maia, seems to locked into his flesh form from the begining, or at least was at the time of his death. I don't remember his body falling into dust or disappearing immediately after he was slain. It is possible that the decendents of Glaurung were purely flesh creatures.

Interesting thought, also one could draw a parallel to Melian, who being a Maia, took a fleshly form and gave birth to Luthien (who was counted among Elves). Melian left her body afterwards to return to Valinor, but her descendants were just Men/Elves, though carrying the Maiar strain...