index fossils

index fossil

noun Geology, Paleontology.
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.
Also called guide fossil.


Origin:
1895–1900

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Collins
World English Dictionary
index fossil
 
n
Also called: zone fossil a fossil species that characterizes and is used to delimit a geological zone

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
index fossil   (ĭn'děks')  Pronunciation Key 
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.
The American Heritage® Science Dictionary
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