Ancient dragon bones are associated with the Prayer skill, by burying the bones they give 500 prayer xp, 2000 Prayer experience when offered at the Ectofuntus, or 1750 Prayer experience when offered at Gilded altar with 2 burners lit, which is the highest xp gained from bones. The only downside of the bones is that they are untradable and can only be achieved as drops from extremely hard dragons.