Index fossil

A species used to date and correlate rocks: widespread, abundant, easily recognised, and short-lived geologically. Ammonite species give Jurassic resolution to under a million years.

Sources

Treatise on Invertebrate Paleontology — glossaries (KU Paleontological Institute, CC BY 4.0)
Earle, S. (2019). Physical Geology, 2nd ed., Chapter 8: Fossils (CC BY 4.0)

Cite this article

Stratum Study. "Index fossil" (Glossary). Stratum Study pack 2026.09, as of 2026-09-16. https://stratum.black/study/glossary/index-fossil. Accessed 2026-09-20.

BibTeX · CSL-JSON

@misc{stratum-index-fossil,
  title        = {Index fossil},
  author       = {{Stratum Study}},
  howpublished = {\url{https://stratum.black/study/glossary/index-fossil}},
  year         = {2026},
  note         = {Glossary article, Stratum Study pack 2026.09, as of 2026-09-16; sources: stratum. Accessed 2026-09-20.}
}

Citations carry the pack version and the article's as-of date so they resolve to the same text later. The facts themselves belong to the sources listed below; cite those for the science.