An important observation to be made about any fossil is the method of preservation. This indicates what happened to the fossil subsequent to its burial, and the kind of environment in which it was originally buried. Not every organism becomes fossilized. Important prerequisites for fossilization are quick burial, and the presence of some hard parts.
Most fossils have some hard parts.
However, organisms sometimes die in anaerobic environments and soft parts can be preserved. But preservation of soft parts is unusual. Below are the different types of preservation. This includes many invertebrate shells composed of calcium carbonate, silica, chitin, or vertebrate bones of calcium phosphate. This will coat and preserve any organism which dies here.