A fossil that is useful for dating and correlating the strata in which it is found.
- ‘These rocks are interbedded in Emsian marine sedimentary successions that are well documented by index fossils.’
- ‘Carboniferous and Permian strata often contain useful index fossils belonging to this group.’
- ‘This ‘dating’ is based on the presence of the ammonite index fossil Dactylioceras tenuicostatum.’
- ‘Stratigraphic occurrences of Carcineretes in the Caribbean Province suggest that this crab should be regarded as an index fossil for the early Maastrichtian.’
- ‘Possibly the species will prove to be an index fossil for the lower Frasnian and uppermost Givetian of the Sauerland and the Maider in Morocco, ‘Ait Ou Amar’.’
- ‘They are very abundant in some Paleozoic formations and include useful index fossils.’