I apologize wholeheartedly for my blurry photography. Just pretend that you're viewing the picture through a sheen of frightened tears.
The skulls are just paper and glue, the sphere-y bit is pre-crumpled paper (to soften the lines), covered in glue, and rolled up. The lower jaw is folded separately. Details drawn in pen.
As for the little skeletons... string and posterboard. The joints are little overhand knots.