WordReference Random House Unabridged Dictionary of American English © 2025
in′dex fos′sil, [Geol., Paleontol.]
  1. Geology, Paleontologya widely distributed fossil, of narrow range in time, regarded as characteristic of a given geological formation, used esp. in determining the age of related formations.
Also called guide fossil. 
  • 1895–1900

Collins Concise English Dictionary © HarperCollins Publishers::
index fossil
  1. a fossil species that characterizes and is used to delimit a geological zone
    Also called: zone fossil
'index fossil' also found in these entries (note: many are not synonyms or translations):
guide fossil

Forum discussions with the word(s) "index fossil" in the title:


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