Mangled bones are obtained when fighting the monsters or rummaging the barbarian skeleton found on the ground within the Ancient Cavern. With any type of logs, a hatchet, and a tinderbox, players can use it on the burnt space (pyre site) to make a pyre ship.
A sure way of getting mangled bones is by killing confused barbarians or lost barbarians, as they always drop them. Note that a bonecrusher will activate for these bones, giving the xp of normal bones.
Note: if rummaging a skeleton at least 2 slots must be free because of the random chance of finding an ancient page for my notes. If you do not have enough slots free, the bones will "disintegrate".
Mangled bones also do not give the Prayer experience bonus that chewed bones give.
If the bones are lost on death, when returning to claim items from the grave, they will have become normal bones.