Fossils can be used to revive prehistoric Pokémon whose Eggs are not placed in the Lab. They are found by scouring. A fossil Pokémon will find its corresponding fossil more easily. The Pokémon does not have to be a Prehistoric Pokémon itself to receive this Scouring boost. When a Pokémon returns with a fossil, it will be placed in the Fossils section of the Inventory.
Once obtained, the owned fossils can be found and revived in the Lab. Reviving a fossil requires 1,500 Interactions, then the revived Pokémon can be placed in the Party if there is an empty spot. Otherwise the user will be prompted to place a Pokémon into a field to make space for the revived Pokémon. Reviving a fossil while Shiny Hunting does not break the chain, as they are not hatched from an Egg. It is not possible to get a Shiny or Albino from reviving fossils.
A revived Pokémon is designated by a Prehistoric icon next to its gender. If a prehistoric Pokémon is placed in the party, it will give a bigger boost to the EXP gained by Eggs of the same species than normal Pokémon do, roughly double the EXP the egg would get if there was no other Pokémon in the party.