Coilopoceratidae

Coilopoceratidae Temporal range: U Cretaceous Turonian-Coniacian.
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	Ammonoidea
Order:	Ammonitida
Suborder:	Ammonitina
Family:	Coilopoceratidae

Coilopoceratidae is a family of generally large, proper ammnites with strongly involute shells from the Upper Cretaceous, Turonian and Coniacian stages. Coilopoceratids have variably compressed shells with flattish to broadly rounded sides and narrowly rounded to sharp keel-like venters. Whorl sections are generally lanceolate. The suture is ammonitic with an overall clumpy appearance.

The Coilopoceratidae are derived from the Tissotiidae by a secondary re-development of an ammonitic suture and of more narrowly compressed shells.

Coilopoceratid genera

Coilopoceras – Coilopoceratidae with a widespread distribution, characterized by well compressed involute shells with rounded flanks and narrow ventral margins and clumpy ammonitic sutures, found in north and west Africa, Syria, Baluchistan, and western North America (Colo, N Mex, Texas).

Glebosoceras – a coilopocerid from Nigeria with a rapidly expanding shell with a fairly sharp venter and clumpy ribs that become more prominent with age. The suture has clumpy saddles and lobes with multiple finger-like projections. Glebosoceras has been included in the Pseudotossiidae ( ex Pseudotossiinae).

Hoplitoides – coilopoceratids in which early whorls have grooved, then flat, and finally narrowly rounded venters; early stages with umbilical tubercles and space ribs, later stages becoming smooth. The suture is similar to that of Glebosoceras but less extreme. Hoplitoides has been found in north and west Africa, Syria, Columbia and Peru.

Herrickiceras

The suture in Coilopoceras is distinct from that of Glebosoceras and Hoplitoides in having a deep, narrow, ventral lobe with wavy sides. The ventral lobe in Glebosoceras and Hoplitoides is broad and shallow. The sutures of Glebosoceras and Hoplitoides are a more strongly ammonitic development of the Hemitissoita (Tissoitiidae) suture. In Coilopoceras the lateral lobes become less sharply digitate.

References

• Arkell, W.J.et al., Mesozoic Ammonoidea in the Treatise on Invertebrate Paleontology, Part L, Mollusca 4. Geol Soc of America and Univ Kansas Pres. R.C. Moore (ed)
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