See text The Cymatoceratidae is a family of Mesozoic and early Cenozoic nautiloid cephalopods and the most abundant of their kind in the Cretaceous.

They are characterized by ribbed, generally involute shells of varied forms - coiled such that the outer whorl envelops the previous one, as with Nautilus, and sutures that are variably sinuous.

[1] First to appear was the large, tightly involute, rapidly expanding Procymatoceras from the Middle Jurassic, followed by the Middle and Upper Jurassic Cymatonautilus which has a wide umbilicus and subquadrate whorl section.

Of the Cymatoceratidae, Cymatoceras has the longest temporal range, extending from the Late Jurassic to the Tertiary Oligocene.

The only other to cross a period boundary is Paracymatoceras which lived during both the Late Jurassic and Early Cretaceous.