What are fossils organisms that existed over a wide area but only a limited time period called

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Index Fossils

Explanation:-

Index fossils are fossils that are preserved in the rock record and are characteristic for a particular geological time period.

Index fossils have a wide distribution geographically and is easily identifiable. But they were there for only a small time period. Hence they are often used to define geological time frames and relate strata datas.

Index fossils are thus fossils organisms that existed over a wide area but only a limited time period