Index fossil

Index fossils ( Orthostratigraphen ) are fossils, which helps you to make the relative age determination of various rock layers. If one finds the same index fossil in sedimentary rocks from different places of the earth, the rocks are approximately the same age. This type of dating is called biostratigraphy.

Requirements for index fossils

An ideal index fossil fulfills the following conditions:

• The relevant characteristics of the species may have existed only a short time to allow a precise dating possible
• The species should have existed in different habitats as possible and therefore be found in as many different Gesteinsfazies
• The fossils must be geographically widespread, so that even the most distant layers can be compared
• The fossils must be easily and precisely defined.
• The fossils must occur in high numbers.

The less these requirements are met, the lower the utility as index fossil.

Examples

Index fossils for the Cambrian are mainly trilobites, Ordovician and Silurian for most graptolites and from the Devonian to the Cretaceous ammonoids represent the most index fossils. In Cenozoic strata often fossil foraminifera and ostracods are used to determine the Faunenfolge in refined scale ( microfossils ).

For the dating of particular interest in connection with the phylogeny of human African sites from the Pliocene and early Pleistocene fossils pigs play an important role. Especially the third molars of the bush pig and giant forest hogs have changed in the past four million years of wide - low to hochkronig - narrow, which is why their construction is a reliable indication of their age.

In a figurative sense

The term is used figuratively to types of prehistoric pottery, of which the adjacent find sites to reflect a cultural province.