Ammonoid

Ammonoids are extinct, typically coiled-shelled cephalopods composing the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish than they are to nautiluses, which they resemble. The earliest ammonoids appeared during the Emsian stage of the Early Devonian, around 410-408 million years ago, with the last species vanishing during or soon after the Cretaceous–Paleogene extinction event approximately 66 million years ago. They are often called ammonites, which is most frequently used for members of the order Ammonitida, the only remaining group of ammonoids from the Jurassic up until their extinction.