''Geisonoceras'' is an extinct orthocerid genus named by Hyatt, 1884, and type for the

Geisonoceratidae Geisonoceratidae is an extinct family of orthoceroid cephalopods endemic to what would be Asia, Europe, and North America from the Middle Ordovician to the Middle DevonianSweet, W. C. 1964. Nautiloidea- Orthocerida; Treatise on Invertebrate Pale ...

established by Zhuravleva in 1959.

Fossil record

Fossils of '' Geisonoceras'' are found in marine strata from the Ordovician until the

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

(age range: from 460.9 to 383.7 million years ago.). Fossils are known from various localities in

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

and Asia.

Species

*†''Geisonoceras heintzi'' Strand 1934 *†''Geisonoceras maclareni'' Murchison 1859 *†''Geisonoceras shumardi'' Billings 1859 *†''Geisonoceras wegelini'' Teichert 1930

Description

Shells are elongate, straight or slightly curved, and slowly expanding with a circular or subcircular cross section, transverse aperture and slight hyponomic sinus. The surface has broad transverse bands with fine growth lines between. Sutures are straight, transverse or slightly oblique. 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 subcentral, necks short and straight, connecting rings slightly expanded into the chambers.Walter A Sweet, 1964. Nautiloidea -Orthocerida, ''Treatise on Invertebrate Paleontology'' Part K, Endoceratoidea, Actinoceratoidea, Nautiloidea. Geological Society of America and Univ Kansas Press. Teichert and Moore (Eds)

References

{{Taxonbar, from=Q16976416 Nautiloids Middle Ordovician first appearances Middle Devonian genus extinctions Paleozoic life of Ontario Paleozoic life of Quebec Orthocerida