Complex sentence: An X-ray analysis performed on the corroded metal found under the vertebrae and thought to be an arrowhead, revealed it was a Roman nail that had been in the ground immediately under the grave by coincidence and had nothing to do with the body.
Split into simpler sentences: An X-ray analysis performed on the corroded piece of metal, found under the vertebrae and thought to be an arrowhead, revealled that it was a Roman nail. It had been in the ground, immediately underneath the grave, by coincidence and had nothing to do with the body.