The Trigonoceratidae is a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of coiled

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 that lived during the period from the

Early Carboniferous Early may refer to: Places in the United States * Early, Iowa, a city * Early, Texas, a city * Early Branch, a stream in Missouri * Early County, Georgia * Fort Early, Georgia, an early 19th century fort Music * Early B, stage name of Jamaican d ...

( Mississippian) to the

Early Permian 01 or 01 may refer to: * The year 2001, or any year ending with 01 * The month of January * 1 (number) Music * '01 (Richard Müller album), ''01'' (Richard Müller album), 2001 * 01 (Urban Zakapa album), ''01'' (Urban Zakapa album), 2011 * ''01011 ...

Diagnosis

Trigonoceratidae comprise members of the order Nautilida characterized by a loosely coiled to evolute shell generally bearing longitudinal ribs or ridges with a whorl section that is oval to subquadrate and varying from compressed (squeezed) to depressed (flattened). (Kummel 1964)

Classification and phylogeny

Taxonomic position

The Trigonoceratidae along with four other related families are combined in the Superfamily Trigonocerataceae in the Treatise,(''ibid'' Kummel) a superfamily. They are also the Triboloceratidae (Flower and Kummel, 1950) which form the Tribolocerataceae within the Centroceratina of the Osnovy according to Shimansky. The Trigonocerataceae and Centroceratina are essentially equivalent as are the Trigonoceratidae and Triboloceratidae.

Derivation

The Trigonerceratidae were derived from the core Centroceratidae (basis for the name Centroceratina) early in the Mississippian along with the longer lived Grypoceratidae. Of the five families of the Trigonocerataceae, the Trigonoceratidae was defined first, by Hyatt in 1884, hence the choice of name.

Generic composition

Seventeen trigonoceratid genera are listed in the Treatise. All but one are found in the Lower Carboniferous of Europe and equivalent Mississippian of North America.(''ibid'' Kummel)

Geographic distribution

Mississippian Genera from North America alone :* '' Chouteauoceras'' :* '' Diodoceras '' :* '' Imonautilus'' Mississippian Genera from North America and Europe (L Carb) :*'' Aphelaeceras'' :*'' Maccoyoceras'' :*'' Rineceras'' :*'' Stroboceras'' :*'' Thrincoceras'' -- -- extends to Lower Permian :*'' Vestinautilus'' Mississippian (L Carb) Genera from Europe :*''

Trigonoceras ''Trigonoceras'' is an extinct genus of prehistoric nautiloids from the nautilid family Trigonoceratidae that lived during the Early Carboniferous in what is now western Europe. ''Trigonoceras'' has a very loosely coiled gyroconic or cyrtoconic ...

'' :*'' Discitoceras'' :*'' Epistroboceras'' :*'' Leuroceras'' :*'' Lispoceras'' :*'' Mesochasmoceras'' :*'' Pararineceras'' :*'' Subclymenia'' Lower Permian Central Asia :*'' Apogonoceras'' -- see ''Thrincoceras''

Morphological variations

''Trigonoceras'', type genus, named by Hyatt, 1844, is unique among the Trigonoceratidae in the

Treatise A treatise is a Formality, formal and systematic written discourse on some subject concerned with investigating or exposing the main principles of the subject and its conclusions."mwod:treatise, Treatise." Merriam-Webster Online Dictionary. Acc ...

. It is the only genus included that has a subtriangular whorl section consisting of a broad concave venter and narrow dorsum. The remaining can be divided on the basis of shell morphology into those that are smooth, at least on the outer whorl, those with numerous equal longitudinal ribs or lirae, and those with prominent longitudinal ridges separated by wide grooves or sulci.(''ibid'' Kummel) Those with smooth whorls include ''Leuroceras'' and ''Mesochasmoceras''; those with numerous longitudinal ribs or lirae include ''Chouteauoceras'', ''Discitoceras'', and ''Rineceras''; and those with prominent, wide spaced, longitudinal ridges are such as ''Stroboceras'' and ''Vestinautilus''. Trigonoceratid genera can also be grouped on the basis of the suture which may be essentially straight and transverse or slightly sinuous, or may have a well defined ventral lobe, or a ventral saddle. Those with straight or slightly sinuous sutures are ''Apogonoceras'', ''Diodoroceras'', ''Discitocdras'', ''Rineceras'', ''Stroboceras'', and ''Thrincoceras''; with a discernible ventral lobe: ''Aphelaeceras'', ''Epistroboceras'', ''Lispoceras'', ''Maccoyoceras'', ''Pararineceras'', ''Subclymenia'', and ''Vestinutilus''; and with a ventral saddle: ''Chouteauoceras'' and ''Leuroceras''. Ventral saddles are also found in the Centroceratidae in '' Carlloceras'' and '' Phacoceras'', in the Grypoceratidae in '' Stenopoceras'' and '' Parastenopoceras'', and in the Syringonautilidae.(''ibid'' Kummel)

References

*Kummel, B. Nautililoidea - Nautilida;

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology,'' published from 1953–2007 by the Geological Society of America and the University of Kansas, then 2009–present by the University of Kansas Paleontological Institute, is a definitive multi-authore ...

Part K, Geol Soc of America and Univ of Kansas press, R.C.Moore (Ed)