Eothinoceratidae is a family of Lower Ordovician

nautiloid Nautiloids are a group of cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and species rich, with over 2,500 recorded species. Th ...

cephalopods included in the

Cyrtocerinida Cyrtocerinida is an order of Ordovician nautiloid cephalopods. The order includes the families Cyrtocerinidae and Eothinoceratidae, as well as the genera '' Bathmoceras'' and '' Rummoceras''. Cyrtocerinids can be characterized by a broad siphu ...

. The family was originally established for the genus '' Eothinoceras''.

Morphology

The Eothinoceratidae as typified by ''Eothinoceras'' is characterized by slender slightly exogastric shells with a rather large siphuncle running along the convex ventral margin. Connecting rings are triangular in section and point straight into the interior of the siphuncle. Septal necks are short to absent.

Genera

In addition to the type genus ''Eothinoceras'' the family is said to include '' Conothinoceras'', '' Desioceras'', '' Margaritoceras'', '' Protothinoceras'', '' Sacerdosoceras'', and '' Saloceras'' summarized here.Eothinoceratidae in PaleoDB
/ref> ''Desioceras'' Cecioni 1953 has a generally straight, narrow shell with a circular cross section covered with lirae. The siphuncle is marginal, septal necks are essentially lacking. Sutures show a rounded ventral saddle. ''Margaritoceras'' Cecioni and Flower 1985 is found in the Obispo Formation, San Lucas, Bolivia.The nautiloid Family Eothinoceratidae from the Floian of the Central Andean Basin (NW Argentina and South Bolivia

/ref> ''Conothinoceras'' and ''Protothinoceras'' were both named by Chen and Teichert in 1987, ''Sacerdosoceras'' and ''Saloceras'' by Evans in 2005. ''Sacerdosoceras'' from Great Britain is early Middle Ordovician in age. ''Saloceras'' from lower in the section in Great Britain and France is Early Ordovician.

References

*Rousseau H Flower, 1964. Memoir 12. The Nautiloid Order Ellesmericerida (Cephalopoda). State Bureau of Mines and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, New Mexico. {{Taxonbar, from=Q24895988 Ellesmerocerida Ordovician animals Prehistoric nautiloid families