Every fossil Pokemon are either part Rock-Type or pure Rock-Type:

Kabuto: Rock/Water

Omantye: Rock/Water

Aerodactyl: Rock/Flying

Lileep: Rock/Grass

Anorith: Rock/Bug

Cranidos: Rock (the only pure Rock-Type Fossil Pokemon)

Shieldon: Rock/Steel (my personal favorite Fossil pokemon)

Tirtouga: Water/Rock (as a matter of fact, Tirtouga is the only Fossil Pokemon to have Rock as it's secondary type)

Archen: Rock/Flying

Tyrunt: Rock/Dragon

Amuara: Rock/Ice