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Cymatoceratidae

The Cymatoceratidae is a family of Mesozoic and early Cenozoic nautiloid cephalopods and the most abundant of this kind in the Cretaceous. They are characterized by ribbed, generally involute shells of varied form - coiled such that the outer whorl envelops the previous, as with Nautilus, and sutures that are variably sinuous.

Cymatoceratids first appear in the Middle Jurassic, derived from the Lower Jurassic Cenoceras ( Nautilidae) and extend as far as the Oligocene.