Index fossils (also known as guide fossils or indicator fossils) are
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
s used to define and identify
geologic periods (or faunal stages). Index fossils must have a short vertical range, wide geographic distribution and rapid evolutionary trends. Another term, Zone fossil is used when the fossil have all the characters stated above except wide geographical distribution, they are limited to a zone and can't be used for correlations of strata.
See also
*
Biostratigraphy#Index fossils
References
{{Reflist
he:מאובן#מאובן מנחה