Index fossil

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Examples of key fossils

Guide fossils ( orthostratigraphs ) are fossils that can be used to determine the relative age of different rock layers. If the same key fossil is found in sedimentary rocks from different places on earth , the rocks are approximately the same age. This type of age determination is called biostratigraphy .

Requirements for index fossils

An ideal index fossil fulfills the following conditions:

  • The relevant characteristics of the species may only have existed for a short time in order to enable the most precise dating possible.
  • The species should have existed in as different habitats as possible and thus be found in as many different rock facies as possible .
  • The fossils must be geographically widespread, so that even distant layers can be compared with one another.
  • The fossils must be easily and clearly identifiable.
  • The fossils must be found in large numbers.

The less these requirements are met, the less useful it is as a guide fossil.

Examples

Key fossils for the Cambrian are mainly trilobites , for Ordovician and Silurian mostly graptolites and from the Devonian to the Cretaceous the ammonoids represent most of the key fossils. In the Cenozoic layers, fossil foraminifera and ostracodes are often used to determine the sequence of fauna on a more refined scale (microfossils).

Pig fossils play an important role in dating the African sites from the Pliocene and early Pleistocene, which are particularly interesting in connection with the human tribal history . Above all, the 3rd molars of the bush pigs and the giant forest pigs have changed from wide-low to high-crowned-narrow in the past four million years, which is why their structure is a reliable indicator of their age.

Figuratively

The term is used in a figurative sense to refer to types of prehistoric pottery whose neighboring sites represent a cultural province.

See also

Individual evidence

  1. ^ Andrew Alden: Index Fossils . About.com. Retrieved January 27, 2013.
  2. ↑ Friedemann Schrenk , Timothy Bromage : The hominid corridor of Southeast Africa. In: Spektrum der Wissenschaft , No. 8/2000, pp. 48-49, ISSN  0170-2971