Brachiopods are a genus of shell fish which date back from the one of the earliest periods in geological history, the Cambrian period, approximately 540 million years ago, and are still alive today with very little morphological changes. Essentially, most people will recognise brachiopods as shell fish fossils, with two parts to their bodies and internal organs. However, through out geological history, certain changes over time have meant that geologists and palaeontologists are able to use brachiopods as zoning fossils, e.g. certain species with a specific pattern or form of shell may have only existed in certain periods. Thus resulting in dating rock formations which the fossils are found in quite easily.