From the beginning of the article: In natural history, fossils provide important evidence of past life forms and their activity (Pellant 1990). Things like ammonites, trilobites and graptolites are the tangible remains of what were once living beings. Although their original chemical composition has changed, the physical structure is often perfectly preserved through a process of petrification. Accordingly, there is a sense in which these creatures have a continuing material existence despite being well and truly dead.