Ashark would not be a good index fossil

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.

Answerhave flowing water either episodically or during only a portion of the year;