What is one example of index fossil

Ammonites were common during the Mesozoic Era (245 to 65 mya), They were not found after the Cretaceous period, as they went extinct during the K-T extinction (65 mya).

Explanation:

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Explanation:

Examples of index fossils include: Ammonites were common during the Mesozoic Era (245 to 65 mya), They were not found after the Cretaceous period, as they went extinct during the K-T extinction (65 mya).

index fossil: The trilobite is in all three outcrops (it is widespread) and in only one layer per outcrop (it is short lived.)