Firstly, let's understand the meaning of ammonities.
It is the name of fossil shell of an cephalopods of the subfamily Ammonoidea.
Now, the answer is:
The scientists were not certain what living ammonites looked like because the insects or creatures living in those shells could be of different looks and as no living ammonite has ever been found(only we have discovered their shells through fossils) thus, no prediction could be done about it.
