你查一下神百那边记录就知道了吧

At first, only Skull Fossils or Armor Fossils can be found depending on the game versionDP or the last digit of the player's Trainer ID numberPt. After obtaining the National Pokédex, however, the game will also yield Helix Fossils, Dome Fossils, Old Ambers, Root Fossils, and Claw Fossils. A number of items that were found rarely prior to obtaining the National Pokédex can also be found more easily now, such as the Evolution stones. Furthermore, in the Pokémon Diamond and Pearl games, Fire Stones, Thunderstones, Sun Stones, Heat Rocks, Icy Rocks, Helix Fossils, and Claw Fossils can be found more easily in Diamond, while Water Stones, Leaf Stones, Moon Stones, Damp Rocks, Smooth Rocks, Dome Fossils, and Root Fossils can be found more easily in Pearl. Pokémon Platinum uses the Trainer ID, much like the Skull and Armor Fossils, to determine which set of treasures is more common during gameplay.
种百的说法就这样

具体几率好像没见过，但确实是概率问题，是能挖到的