how do fossils show the change of sea level?

Question: how do fossils show the change of sea level?
- Keywords:
  fossil,
  sea level
Asked by bug to Sophie on 15 Mar 2018.
- Sophie Williams answered on 15 Mar 2018:
  
  Because some like to live on the land and some like to live in the sea so if you find certain types you know whether the sea was there or not

Question: how do fossils show the change of sea level?