I've found bones and pieces many times out detecting, most likely animal bones from the farms I detect on that were used for food; I would imagine that others have done similar.
Are you asking generally about bones, or did you mean other types of bones, human perhaps?
Yep, I have found deer skulls before. I once found a fox skeleton which I gave to a friend that like anatomy who makes displays out of animal bones. He ended up getting very very excited when I told him I saw a fox skeleton and started asking for coordinates and such so I went out there with a garbage bag and grabbed it for him. He was thrilled and worked on the display right away.
years ago my cousin found a mound and started digging. It was near old gold mine and i had a bad feeling about it. In the area also was an Indian camp where we found beads and arrows. All of a sudden he started yellin for me and i walked over to him. He had a human skull with a large hole in it in his hands. We called the sheriff and they came out for a look. After 3 weeks we got a call from the sheriff of what they thought it was. They said it was not indian but maybe the bones dated to about the 1920s. We went back and the area had no trespassing signs everywhere.