Irish researchers discovered in 2015 that the Petrous portion of the temporal bone preserves DNA much better than other parts of the body, so that is where researchers have tried to get it ever since. It is an extremely hard and dense bone, hence its name. They have even gone back to fossil remains of ancient humans that they thought they could not get DNA from and extracted it, knowing now where to best look for it. DNA degrades more quickly in other areas. Just one of the little technique things in science that can push the field forward as much as a new discovery.