Theyre not excavated but dug only for fun (4)
I believe the answer is:
ribs
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for ribs that I've seen before include "Makes fun of - bones" , "Arched bones extending from the spine" , "cage" , "Bones in chest, may be floating" , "Chest bones, tasty when spare" .)