ammonite vs fossil

ammonite and fossil both are nouns.

Word	Noun	Adjective	Verb	Adverb
ammonite	Yes	No	No	No
fossil	Yes	Yes	No	No

As nouns, fossil is a hypernym of ammonite; that is, fossil is a word with a broader meaning than ammonite:

ammonite: one of the coiled chambered fossil shells of extinct mollusks
fossil: the remains (or an impression) of a plant or animal that existed in a past geological age and that has been excavated from the soil

ammonite (noun)	fossil (noun)
one of the coiled chambered fossil shells of extinct mollusks	the remains (or an impression) of a plant or animal that existed in a past geological age and that has been excavated from the soil
	someone whose style is out of fashion

ammonite (adjective)	fossil (adjective)
	characteristic of a fossil