So what are all the items that can be dug up in game from mounds in caves like twist mountain for example? There are no fossils anywhere in game in any of these mounds outside of the underground?
As for the fossil, I honestly can't recall, I know it was either Sinnoh or Unova, but if your saying that wasn't available outside the underground in Sinnoh, then it must have been Unova. I can't recall exactly where I found it, but I'm pretty sure I found it in one of the caves on a rock or in a corner. I don't even remember what it was, I sold it right away.