Minecraft wiki entry for Fossil, associated text: Many fossils that have generated on a superflat world in a swamp biome.
A fossil that has generated underwater, inside an underwater ravine.
A fossil that generated mid-air in a flooded cave.
A fossil generated at the bottom of an ocean.
A fossil generated in an ocean ravine.
Another fossil generated at the bottom of an ocean.
A fossil that generated just below the seafloor.