An extensive number of fossil cephalopods usually very rich in Mesozoic stones. See ammonite.
A superfamily of tetrabranchiate cephalopods, including those which have an external layer of two principal layers, with a short smooth chamber together with siphonal cavity extending forward. It includes the majority of the order Ammonea.
Definition for "ammonitoidea"
An extensive number of fossil cephalopods usually very…