Answer:
Index Fossil
Step-by-step explanation:
index fossil, any animal or plant preserved in the rock record of the Earth that is characteristic of a particular span of geologic time or environment. A useful index fossil must be distinctive or easily recognizable, abundant, and have a wide geographic distribution and a short range through time.
Kids Definition: A fossil that is found over a relatively short span of geological time and can be used in dating formations in which it is found.