Ammonite, say (6)
I believe the answer is:
fossil
'ammonite say' is the definition.
(I know that ammonite is a type of fossil)
This is all the clue.
(Other definitions for fossil that I've seen before include "Ammonite, for example" , "Ancient remains embedded in rock" , "Relic of former life preserved in stone" , "Ancient remains preserved in rock" , "The remains of a plant or animal that existed in a past geological age" .)