The Trigonoceratoidea are a superfamily within the

Nautilida The Nautilida constitute a large and diverse order of generally coiled nautiloid cephalopods that began in the mid Paleozoic and continues to the present with a single family, the Nautilidae which includes two genera, ''Nautilus'' and ''Allonauti ...

that ranged from the

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

to the

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

, thought to have contained the source for the

Nautilaceae The Nautilaceae form one of five superfamilies that make up the Nautilida according to Bernard Kummel (1964), and the only one that survived past the Triassic. The Nautilaceae comprise six families: Nautilidae, Paracenoceratidae, Pseudonautili ...

in which ''

Nautilus A nautilus (; ) is any of the various species within the cephalopod family Nautilidae. This is the sole extant family of the superfamily Nautilaceae and the suborder Nautilina. It comprises nine living species in two genera, the type genus, ty ...

'' is found. Trigonoceratoidea are characterized by open-spiraled, gyroconic, to closed, nautiliconic shells in which the

Whorl A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). In nature File:Photograph and axial plane floral diagra ...

section is quadrate in primitive forms; the

venter Venter or Venters is an Afrikaans (and rarely, Jewish) surname, and may refer to: Venter * AJ Venter (b. 1973), South African rugby union footballer * Al J Venter (b. 1938), author * André Venter (b. 1970), South African rugby union footballer * ...

typically narrow to acute, the dorsum broad. In some advanced forms, the venter may become concave or broad and rounded, and in some, the surfaces may be strongly

lirate Lirae (singular lira) are fine lines or ridges (much finer than ribs) that are a sculptural feature of the outside of the shells of various organisms. The term is commonly applied to the shells of molluscs such as gastropods, bivalves and naut ...

Classification and phylogeny

The Trigonoceratoidea are based on the family

Trigonoceratidae The Trigonoceratidae is a family of coiled nautiloid cephalopods that lived during the period from the Early Carboniferous ( Mississippian) to the Early Permian. Diagnosis Trigonoceratidae comprise members of the order Nautilida characterized ...

Alpheus Hyatt Alpheus Hyatt (April 5, 1838 – January 15, 1902) was an American zoologist and palaeontologist. Hyatt served as the founding president of the American Society of Naturalists from 1883 to 1884 and was the founding editor of the journal '' T ...

, 1884, with which other

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

ally related families are combined, and are equivalent to the abandoned Centroceratida of Flower in Flower and Kümmel 1950, and to the Centroceratina of Shimanskiy 1957, revised to the Centrocerataceae, Shimanskiy 1962. The Trigonoceratoidea combine five families, the type, Trigonoceratidae, along with the

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 ...

Grypoceratidae Grypoceratidae is the longest-lived family of the Trigonoceratoidea, or of the near equivalent Centroceratina; members of the Nautilida from the Upper Paleozoic and Triassic.Kummel,B. 1964. Nautiloidea-Nautilida, Treatise on Invertebrate Paleont ...

, Permoceratidae, and

Syringonautilidae Syringonautilidae is a family of Nautiloidea from the middle to late Triassic. Syringonautilidae comprise the last of the Trigonoceratoidea and are the source for the Nautilaceae which continued the Nautiloidea through the Mesozoic and into the ...

. Phylogenetic study and age show that the Centroceratidae are the root stock in spite of having been first recognized 16 years after the Trigonoceratidae were first described. The Centroceratidae gave rise to the Trigonoceratidae and Grypoceratidae in the early

Mississippian Mississippian may refer to: * Mississippian (geology), a subperiod of the Carboniferous period in the geologic timescale, roughly 360 to 325 million years ago * Mississippian cultures, a network of precontact cultures across the midwest and Easte ...

, while continuing until the very

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 ...

. The Trigonoceratidae which ranged into the Permian left no descendants. The Grypoceratidae which ranged almost to the end of the Triassic gave rise to two small families, the Permian Permoceratidae and the Triassic Syringonautilidae. The Syringonautilidae, in turn, are the source for the Nautilidae (Nautilaceae) which contain the genus ''Nautilus''.

Families

The

, type family, named by Hyatt, 1884, are loosely coiled to

evolute In the differential geometry of curves, the evolute of a curve is the locus (mathematics), locus of all its Center of curvature, centers of curvature. That is to say that when the center of curvature of each point on a curve is drawn, the result ...

, with oval to

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