Ammonite

[Sarah]

A fossil cephalopod shell related to the nautilus. There aremany genera and species, and all are extinct, the typical formshaving existed only in the Mesozoic age, when they were exceedinglynumerous. They differ from the nautili in having the margins of thesepta very much lobed or plaited, and the siphuncle dorsal. Alsocalled serpent stone, snake stone, and cornu Ammonis.

[Zipporah Schumaker]

an extinct sea creature (= one that no longer exists) often found as a fossil (= an animal turned into rock) , with a flat, spiral shell

[Sonia]

An ammonoid that belongs to the order Ammonitida, typically having elaborately frilled suture lines.