The Trigonoceratidae is a

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

of coiled

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 species ...

cephalopods that lived during the period from the

Early Carboniferous Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * Early ...

( 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 (Son of Dave album), ''01'' (Son of Dave album), 2000 * 01 (Urban ...

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 The Trigonoceratoidea are a superfamily within the Nautilida that ranged from the Devonian to the Triassic, thought to have contained the source for the Nautilaceae in which ''Nautilus'' is found. Trigonoceratoidea are characterized by open-spir ...

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 The Centroceratidae is the ancestral family of the Trigonoceratoidea and of the equivalent Centroceratina; extinct shelled cephalopods belonging to the order Nautilida Diagnosis The Centroceratidae, which range from the Middle Devonian to the ...

(basis for the name

Centroceratina The Trigonoceratoidea are a superfamily within the Nautilida that ranged from the Devonian to the Triassic, thought to have contained the source for the Nautilaceae in which ''Nautilus'' is found. Trigonoceratoidea are characterized by open-spir ...

) 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'' :*'' 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 formal and systematic written discourse on some subject, generally longer and treating it in greater depth than an essay, and more concerned with investigating or exposing the principles of the subject and its conclusions."Treat ...

. 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

in ''

Carlloceras The Centroceratidae is the ancestral family of the Trigonoceratoidea and of the equivalent Centroceratina; extinct shelled cephalopods belonging to the order Nautilida Diagnosis The Centroceratidae, which range from the Middle Devonian to the ...

'' and ''

Phacoceras The Centroceratidae is the ancestral family of the Trigonoceratoidea and of the equivalent Centroceratina; extinct shelled cephalopods belonging to the order Nautilida Diagnosis The Centroceratidae, which range from the Middle Devonian to the ...

'', 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'' (or ''TIP'') published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and co ...

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