Deltoidonautilus cassinianus

Deltoidonautilus cassinianus

(Foord & Crick, 1890)

Common name Nautilus
Fossil group Molluscs
Order Nautilida
Family Hercoglossidae
Genus Deltoidonautilus
Taxonomic status Accepted
Geological age Ypresian

Summary

Deltoidonautilus cassinianus was a free-swimming chambered cephalopod in the London Clay sea. Its tightly coiled shell contained gas-regulated chambers for buoyancy, allowing the animal to cruise above the seabed and adjust its position in the water without constant active swimming.

Its diet is inferred from nautiloid biology rather than preserved stomach contents. It was probably an opportunistic predator and scavenger, taking small marine animals and carrion. The species belonged to a diverse group of Eocene nautiloids that occupied the seas long after ammonites had disappeared.

Quick Identification

Look for: a fairly large, tightly coiled Deltoidonautilus with a broad rounded whorl and gently sinuous chamber sutures; compare carefully with D. sowerbyi, which has a narrower, more sharply converging outer profile.

Diagnostic Features

  • Shell is planispiral and strongly involute, with most earlier whorls concealed.
  • Whorl section is broad and rounded rather than strongly compressed.
  • Chamber sutures form gently sinuous curves across the flank.
  • Umbilical region is small because of the strong degree of whorl overlap.
  • Overall shell is robust and lacks the distinctly narrow, peaked outer profile typical of Deltoidonautilus sowerbyi.

Fossil Details

Typical size
About 90 mm.
Fossil material
Shell, Internal Mould / Cast
Preservation
The original aragonitic shell is often lost, leaving a sideritic, phosphatic or pyritic internal mould. Weathering can erase the sutures and compression can alter the whorl section, both of which are important for separating this species from other London Clay nautiloids.

Similar Species

Recorded Fossil Sites

Synonyms & Previous Names

Nautilus cassinianus; Hercoglossa cassiniana

References

  • Foord, A. H.; Crick, G. C. (1890). On some new and imperfectly-defined species of Jurassic, Cretaceous, and Tertiary Nautili contained in the British Museum (Natural History). The Annals and Magazine of Natural History, Series 6, 5, 388–409 View reference
  • Hewitt, R. A. (2002). A review of the Early Eocene nautiloids of the London Clay Formation (upper division C to lowest division E) of south-east England, with particular reference to concretionary horizons and faunules in the offshore facies strata at Southend-on-Sea, Essex and in the adjacent cliffs of the Isle of Sheppey, Kent. Tertiary Research, 21(1–4), 39–50 View reference
Last Reviewed
15 August 2026 Reviewed by Sam Harris