Root Fossil

In Hoenn's Desert on Route 111, you can come across the Root Fossil and Claw Fossil. The Root Fossil can be given to a scientist at Devon Corporation, where it will be revived into a living Lileep.

In Pokémon Ruby and Sapphire, you have only one chnace to acquire one of the fossils. You must select which one you want, as the other fossil will sink into the sand forever. In Pokémon Emerald, you can select one, and after defeating the Elite Four, return for the other underground.