Warm Sea periodically laps second egg fossil (8)
I believe the answer is:
ammonite
'fossil' is the definition.
(ammonite is a kind of fossil)
'warm sea periodically laps second egg' is the wordplay.
I cannot quite see how this works, but
'second' could be 'mo' (both are short periods of time) and 'mo' is found within the answer.
'egg' could be 'nit' (a nit is an insect egg) and 'nit' is present in the answer.
The remaining letters 'ame' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ammonite that I've seen before include "old enemy of Israelites" , "shelled to extinction?" , "Common fossil" , "Type of explosive" , "marine fossil!" .)