Which phrases describe organisms that formed index fossils? check all that apply.

First an INDEX FOSSIL is any animal or plant preserved in the rock, record of the Earth that is characteristic of a certain geologic time or environment.

Guiding us with the definition above some phrases can be:

For example, Trilobites are a very good index fossil, because they lived in all parts of the ocean, had a hard and large shell, and were enough species to compare in the time range they were alive.