Organisms with hard parts stand a good chance of being fossilized if they are rapidly buried by sediment.
The processes of fossilization are complex with many stages from burial to discovery as a fossil. Organisms with hard parts such as a mineralized shell, like a trilobite or ammonite, are much more likely to become fossilized than animals with only soft parts such as a jellyfish or worms.
Body fossils of plants and animals almost always consist only of the skeletonized or toughened parts because soft tissues are destroyed by decay or by scavengers.
Even hard parts can be destroyed by natural processes such as wave action or can be eaten or destroyed by other organisms like fungi and algae. Many species of plant and animal fossils are known only from their fragments.
The remains of an organism that survive natural biological and physical processes must then become quickly buried by sediments. The probability for an organism to become fossilized increases if it already lives in the sediment , and those on the sea floor are more readily fossilized than those floating or swimming above it.
Learn more about how fossils form at FossilMuseum.net.
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