Don't forget; if you don't get what you're searching for underground, you can always soft reset and try again. The items are arranged randomly whenever you go underground for the first time on any given day. If you redo your first time, it'll be different.
Also, make sure to note that you can only get shield fossils in pearl, and skull fossils in diamond. All the rest (claw, root, helix, dome, and old amber) are in both.
Also, make sure to note that you can only get shield fossils in pearl, and skull fossils in diamond. All the rest (claw, root, helix, dome, and old amber) are in both.