Most fossils are found in rocks either as minerals or as cast as and moulds. Few original body parts are found, the most common being bones and shells. Soft parts have usually disappeared.

The lack of soft parts has made it difficult for scientists to work out what many ancient creatures were really like. Scientists even have this problem with popular and famous fossils such as those of dinosaurs.

Fossils are mainly found where animals and plants were buried by silt being deposited on top of them, so they are more common in the sea than on land.