Ammonite + stand Ammonite 15cm 12.5cm 2cm Aioloceras (Cleoniceras) sp. ammonite fossil from the Cretaceous of Madagascar. It exhibits gorgeous mineralization within the chambers, each separated by white calcite scepta (divisions). Ammonites were predatory mollusks that resembled a squid with a shell. These cephalopods had eyes, tentacles, and spiral shells. They are more closely related to a living octopus, though the shells resemble that of a nautilus. Ammonites appeared in the fossil record about 240 million years ago and they barely survived several major extinction events. The last lineages disappeared 65 million years ago at the end of the Cretaceous.