index fossil

Example Sentences

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So distinctive is this fossil that paleontologists often use it as an index fossil to determine the age of rock layers.

From Science Daily

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