Ammonites are an extinct group of marine invertebrate animals in the subclass Ammonoidea of the class Cephalopoda.

These molluscs are more closely related to living coleoids (i.e. octopuses, squid, and cuttlefish) than they are to shelled nautiloids such as the living Nautilus species.

The earliest ammonites appear during the Devonian, and the last species died out during the Cretaceous–Paleogene extinction event.

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