Dragon Skulls are rare drops from Ender Dragons and are common drops for Boneheads. It has several uses that make it unique from other items. Only Ender Dragons and Boneheads can drop Dragon Skulls, however, and no other dragonlike boss can have a chance of dropping this item.
Dragon Skulls can be placed on the ground as decoration, sort of like Dragon eggs. They can also mine things slightly faster (1.3x) and they can be worn or be put on another mob. The skull stays the same size for all mobs, so big mobs like Ghasts can wear the skull, but the skull won't be very visible. Wearing a Dragon Skull does not make the player evil or a Bonehead, but it does prevent them from receiving the Bone effect, which causes the Player to have traits like a Skeleton (will burn in sunlight, arrows deal less damage but they shoot faster).