Fossil Formation

Fossil Formation Process

A Crinoid Story

The fossil formation process, called fossilization, is a complex and a rarity for given organism. Hard parts of an organism, such as a mineralized shell of an ammonite, or exeskeleton of an arthropod are much more likely to become fossilized than soft parts. One key to fossilization is burial, particular by sediment, in a marine environment. The crinoid is an example of an animal that left a poorly fossilized due to its delicate parts. This explains why most crinoids, for example, are found only as stem pieces. Since crinoids were not usually buried quickly, their hard stem parts are far more frequently found as fossils. Observations of rare living crinoids have shown that they will rapidly disarticulate within a few days of death. Rapid burial, in contrast, prevents this disintegration, and thus explains a few localities where beds of delicate crinoids, starfish and brittle stars are preserved in their entirety.