Cymatoceratidae

Cymatoceratidae Temporal range: Middle Jurassic–Oligocene PreЄ Є O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	Nautiloidea
Order:	Nautilida
Superfamily:	Nautilaceae
Family:	Cymatoceratidae Spath, 1927
Genera
Procymatoceras Cymatonautilus Paracymatoceras Cymatoceras Eucymatoceras Heminautilus Anglonatutilus Deltonautilus Epicymatoceras Syrionautilus

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.^[1]

Cymatoceratids first appear in the Middle Jurassic, derived from the Lower Jurassic Cenoceras (Nautilidae) and extend as far as the Oligocene.^[1]

Taxonomy

The Cymatoceratidae includes ten known genera, beginning with the Middle Jurassic Procymatoceras and Middle and Upper Jurassic Cymatonautilus. Procymatoceras is described as tightly involute, large, rapidly expanding; with early whorl sections more rounded (than latter). Cymatonautilus has a subquadrate whorl section and wide umbilcus. Procymatoceras and Cymatonautilus are followed by Cymatoceras and the similar Paracymatoceras.^[1]

Cymatoceras has the longest temporal range of any of the Cymatoceratidae, from the Upper Jurassic to the Oligocene. Paracymatoceras' is much shorter, extending only to the Lower Cretaceous. Cymatoceras has a generally subglobular, variably involutie shell with a rounded whorl section, conspicuous ribs, and suture that is only slightly sinuous. Paracymatoceras differs primarily in that the suture in more sinuous with deep, broadly rounded lateral lobes.^[1]

Genera from the Lower Cretaceous are the subglobular involute Eucymatoceras with prominent ribs that form a deep v-shaped ventral sinus, the involute and compressed Heminautilus with sides converging on a narrow flattened venter. and Anglonautilus with large transverse foldlike undulations, which is also known from the Upper Cretaceous.^[1]

Upper Cretaceous genera, in addition to Anglonautilus, are Deltocymatoceras, a broadly arched, involute form with a keel-like ridge running along the venter, i.e. outer, rim; the discoidal and widely evolute Epicymatocers with a narrow flattened venter, and the subglobular Syrionautilus with acute ribs that are widely spaced.^[1]

References

1. ^ ^{a b c d e f} Kummel 1964. Nautiloidea-Nautilida; Treatise on Invertebrate Paleonology Part K; Teichert and Moore (eds), Geological Society of America and University of Kansas press

• The Paleobiology Database entry for Cymatoceratidae