ANSWER:
A "shark" would not be a "good index fossil" because the "species has survived for too long".
EXPLANATION:
- Index fossil are basically used to make study and identify about its nature, geographic periods.
- The formation of index fossil is made through the preserving animal or plants on the "rock record" of Earth.
- This pattern is noticed, studied which would result in providing us properties of certain life time of geologic time and environment.
- Example of index fossil is Ammonites.
