Polished Pair of Ammonite FossilsSmooth Polished Ammonite sliced into 2 matching sides allowing view of the interior of this ancient creature Ammonite Fossil Ammonites began appearing over 410 million years ago, during the Early Devonian period, vanishing soon after the Cretaceous mass extinction event 66 million years ago. They are most closely related to living octopuses, squid, and cuttlefish. The name "ammonite" was inspired by the spiral shape of their fossilized shells, which