Loone has marked the location of another leviathan on your map, but she has found that it is missing some of its bones.
Quest Location
This quest starts after you complete Eldin's Colossal Fossil.
Completing the Quest
In the Hebra Great Skeleton cave, talk to Loone and she points out that one of the skeleton's fin bones and spine bones is missing.
Look in the south wall for a wall of boulders. You can see a bone sticking out. Break the boulders, then use Ultrahand to move the fin bone into place. The bone will automatically attach itself if you have positioned it correctly.
Near the missing piece of spine, there is a large chunk of ice. Melt this ice to find the missing spine piece. Use Ultrahand to move it into place. The bone will automatically attach itself if you have positioned it correctly.
Quest Reward
Talk to Loone after you put the bones in place to get 50 rupees.