They became extinct. They changed their diets. They hid in marine sediments. They migrated to new environments.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Index fossils help scientists estimate the age of a rock because index fossil species only existed for a relatively short time. What happened to the species that are now used as index fossils?
Possibilities:
- They became extinct.
- They changed their diets.
- They hid in marine sediments.
- They migrated to new environments.

They became extinct.