Ammonites (Apoderoceras) were predatory mollusks that resembled a squid with a shell.

They are more closely related to a living octopus, though the shells resemble that of a nautilus.

True ammonites appeared in the fossil record about 240 million years ago.

[3] The International Commission on Stratigraphy (ICS) has assigned the First Appearance Datum of genus Apoderoceras and of Bifericeras donovani the defining biological marker for the start of the Pliensbachian Stage of the Jurassic, 190.8 ± 1.0 million years ago.

Jurassic of Argentina, Hungary, Italy, Portugal, the United Kingdom [4]