Faunal stages are a subdivision of geologic time used primarily by paleontologists who study fossils rather than by geologists who study rock formations. Typically, a faunal stage will consist of a series of rocks that contain similar fossils. There will be one or more index fossils that are usually common, easily recognized, and limited to a single, or at most a few, stages. Thus, for example, a North American paleontologist finding fragments of the trilobite Olenellus would identify the beds as being from the Waucoban Stage whereas fragments of a later trilobite such as Elrathia would identify the stage as Albertan. The geologic time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of the Earth. ... A paleontologist carefully chips rock from a column of dinosaur vertebrae. ... A fossil Ammonite Fossils (from Latin fossus, literally having been dug up) are the mineralized or otherwise preserved remains or traces (such as footprints) of animals, plants, and other organisms. ... A geologist is a contributor to the science of geology, studying the physical structure and processes of the Earth. ... Index fossils (or zone fossils) are fossils used to define and identify geologic periods (or faunal stages). ... Orders Agnostida Redlichiida Corynexochida Lichida Phacopida Proetida Asaphida Harpetida Ptychopariida doubtful order Nektaspida Trilobites are extinct arthropods in the class Trilobita. ...

Faunal stages were very important in the 19th and early 20th Century as they were the major tool available for dating rock beds until the development of seismology and radioactive dating in the second half of the 20th Century. Seismology (from the Greek seismos = earthquake and logos = word) is the scientific study of earthquakes and the movement of waves through the Earth. ... Radiometric dating is a technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, and the current abundances. ...

Faunal stages are regional. They often include many formations of differing rock types that were being laid down in different environments at the same time. In recent years, regional and global correlations of rock sequences have become relatively certain and there is less need for faunal labels to refine the age of formations. There has been a tendency to use European and, to a lesser extent, Asian, stage names for the same time period world wide even though the faunas in other regions may have little in common with the stage as originally defined.

See also

• Body form