The grim discovery was made by a woman walking her dog on the main Sheffield road at Oxspring, Barnsley, south Yorkshire. She alerted police after finding it on a grass verge.
Police said they knew who the man was, but added: "It is not yet possible to give the identity of the man as relatives are away."
They have revealed that the man, who was in his eighties, died from natural causes and was buried in December 1995.
Police are believed to be examining a number of theories - including black magic or simple ghoulish curiosity.Reuse content