Answer:-
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
