Dawsonoceratidae is an extinct family of orthoconic nautiloid cephalopods that lived in what would be

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

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 ...

from the Late Ordovician through the Middle

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 ...

from about 480–390

mya Mya may refer to: Brands and product names * Mya (program), an intelligent personal assistant created by Motorola * Mya (TV channel), an Italian Television channel * Midwest Young Artists, a comprehensive youth music program Codes * Burmese ...

, existing for approximately .PaleoBiology Database: Dawsonoceratidae, basic info
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Taxonomic Position

Dawsonoceratidae was named by Flower (1962) and included in the Michelinoceratida.R. H. Flower. 1962, Notes on the Michelinoceratida Memoir 10 Part 2 New Mexico Bureau of Mines and Mineral Resources, Socorro New Mexico. It was assigned to the Orthocerida by Walter Sweet in Teichert ''et al.'' 1964Sweet W. A. 1964, Nautiloidea - Orthocerida, Treatise on Invertebrate Paleontology Part K, Mollusca 3, Curt Teichert & R.C.Moore (eds) as part of the Orthocerataceae. The type genus is '' Dawsonoceras'', named by Hyatt in 1883.

Morphology

Dawsonoceratidae are michelinocerids (Orthocerida) with the internal pattern of the

Michelinoceratidae Orthoceratidae is an extinct family of actively mobile carnivorous cephalopods, subclass Nautiloidea, that lived in what would be North America, Europe, Asia, Africa, and Australia from the Ordovician through Triassic from 490—203.7 mya, exis ...

except that the siphuncle segments, which are generally tubular, are constricted at the septal foremina (the openings through with the siphuncular tissues pass). This feature is also found in Silurian ''Kionoceras'', but less developed. Septal necks are short and generally recumbent. The type genus, ''Dawsonoceras'' and its close relative ''Dawsonocerina'' are further characterized by having orthoconic shells with conspicuous annulations, covered by transverse, scalloped or festooned lirae which in some are also longitudinal. Annulations consist of narrow encircling ribs that may be somewhat oblique, separated by generally wider areas in between

Genera

The Dawsonoceratidae comprise six known genera, ''Dawsonoceras'', the type, ''Anaspyroceras'', ''Calocyrtocerina'', ''Dawsonocerina'', ''Metaspyroceras'', and ''Palaeodawsonocerina''. ''Anaspyroceras'', named by Shimizu and Obata (1935) and ''Metaspyroceras'', named by Foeste (1932), were previously included in the orthoceratid subfamily Leuroceratinae, which is no longer considered a valid taxon, and reassigned to the Dawsonoceratidae. ''Anaspyroceras'' and ''Metaspyroceras'' differ from Flowers definition of the Dawsonoceratidae in that the septal necks are othochoanitic rather than recumbent and siphuncle segments are without noted constrictions. ''Calocyrtocerina'', named by Chen (1981) was originally included in the

Paraphragmitidae Paraphragmitidae is an extinct family of actively mobile aquatic carnivorous cephalopods belonging to the subclass Orthoceratoidea endemic to what would be Asia and Europe during the Silurian living from 436 to 418.7 mya, existing for approxima ...

of Flower and Kümmel 1950. ''Palaeodawsonocerina'' started off as ''Spyroceras senckenbergi'' Teichert (1932) and redefined by Kroger and Isakar (2006) as the type species of ''Paleodawsonocerina'' (''P. senckenbergi'')

References

* ''Fossils'' (Smithsonian Handbooks) by David Ward {{Taxonbar, from=Q5242697 Prehistoric nautiloid families Ordovician cephalopods Silurian animals Paleozoic cephalopods of North America Paleozoic animals of Europe Devonian cephalopods Middle Devonian extinctions