High Quality Content by WIKIPEDIA articles! Xenocephalites is an extinct ammonoid cephalopod genus from the early Middle Jurassic belonging to the suborder Ammonitina and to the superfamily Stephanocerataceae. The Ammonoidea constitute a subclass of extinct cephalopods found in marine sediments from the Early Devonian through the Cretaceous (479—65 mya), existing for approximately 414 million years. Bearing an external shell, ammonoids superficially resemble nautiloids, such as the modern Nautilus . however, based on similarity of the radulas, they are more closely related to modern coleoids; squid, octopus, and cuttlefish.

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