''Ellesmeroceras'' is the type genus for the

Ellesmeroceratidae The Ellesmeroceratidae constitute a family within the cephalopod order Ellesmerocerida. They lived from the Upper Cambrian to the Lower Ordovician. They are characterized by straight and endogastric shells, often laterally compressed, so the do ...

, a family of primitive

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

cephalopods, that is characterized by its small, generally compressed, gradually expanded,

orthoconic An orthocone is an unusually long straight shell of a nautiloid cephalopod.; During the 18th and 19th centuries, all shells of this type were named ''Orthoceras'', creating a wastebasket taxon, but it is now known that many groups of nautiloids d ...

shell, found in Lower

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...

marine sediments. The septa are close spaced and the

siphuncle The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and ...

is ventral, about 0.2 the diameter of the shell. Septal necks are typically orthochoanitic (short, straight) but may slant inwardly ( loxochoanitic) or reach halfway to the previous septum ( hemichoanitic). Connecting rings are thick. As common for the

Ellesmerocerida The Ellesmerocerida is an order of primitive cephalopods belonging to the subclass Nautiloidea with a widespread distribution that lived during the Late Cambrian and Ordovician. Morphology The Ellesmerocerida are characterized by shells that ...

, ''Ellesmeroceras'' has diaphragms within the siphuncle tube. The type species, ''Ellesmeroceras scheii'', named by Foeste, 1921, was first found on

Ellesmere Island Ellesmere Island ( iu, script=Latn, Umingmak Nuna, lit=land of muskoxen; french: île d'Ellesmere) is Canada's northernmost and third largest island, and the tenth largest in the world. It comprises an area of , slightly smaller than Great Bri ...

in the Canadian arctic, from whence the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

gets its name. ''Ellesmeroceras'' is one of three straight shelled Ellesmeroceratids, the other two being ''

Ectenolites ''Ectenolites'' is a genus of small, slender, cylindrical Ellesmeroceratids that resemble '' Ellesmeroceras'' but are smaller and proportionally narrower. Septa, as typical for ellesmerocerids, are close spaced with shallow lobes on either flank ...

'' and ''

Eremoceras ''Eremoceras'' is a genus in the Ellesmeroceratidae which lived during the Early Ordovician, characterized by an orthoconic adult stage, similar to ''Ellesmeroceras'', but with the dorsal side of the adult living chamber somewhat convex, and a ju ...

''. It differs from ''Ectenolites'', from which it is probably derived, in being stouter and proportionally wider, and from ''Eremoceras'' in being more straight overall.

References

*Rousseu H Flower, (1964). "The Nautiloid Order Ellesmeroceratida (Cephalopoda)" New Mexico Bureau of Mines and Mineral Resources Memoir 12. *W.M Furnish & Brian F. Glenister (1964). ''Nautiloidea - Ellesmerocerida. Treatise on Invertebrate Paleontology, Part L. (Nautiloidea)''. Geological Society of America and Univ. Kansas Press. {{Taxonbar, from=Q5365267 Ellesmerocerida Paleozoic life of Nunavut Prehistoric nautiloid genera