index fossil

noun

, Geology, Paleontology.

1. a widely distributed fossil, of narrow range in time, regarded as characteristic of a given geological formation, used especially in determining the age of related formations.

index fossil

noun

1. a fossil species that characterizes and is used to delimit a geological zone Also calledzone fossil

index fossil

/ ĭn′dĕks′ /

1. The fossil remains of an organism that lived in a particular geologic age, used to identify or date the rock or rock layer in which it is found. The best type of index fossils are usually those of swimming or floating organisms that evolved quickly (and therefore did not cover a long span of geologic history) and were able to spread over large areas. Ammonites and graptolites are good index fossils.

Word History and Origins

Origin of index fossil¹

First recorded in 1895–1900

Example Sentences

In other cases, researchers can date fossilized remains using nearby “index fossils” of species known to have existed during a specific narrow time frame.

From Scientific American

The grounds were often more interesting than the matches, the All England Lawn Tennis and Croquet Club being such an index fossil from the nineteenth century.

From The New Yorker