Trigonoceratoidea

The Trigonoceratoidea are based on the family Trigonoceratidae of Alpheus Hyatt, 1884, with which other phylogenetically 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, Grypoceratidae, Permoceratidae, and Syringonautilidae. 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, while continuing until the very Early Permian. 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 Trigonoceratidae, type family, named by Hyatt, 1884, are loosely coiled to evolute, with oval to subquadrate, compressed to depressed whorl sections, and generally with longitudinal ridges or lirae. Sutures are typically slightly sinuous; the siphuncle small, subcentral, and orthochoanitic. In all the umbilicus is open and perforate. It includes some 17 genera.

The Centroceratidae, ancestral stock, proposed by Hyatt in 1900, consist of gyroconic to evolute and involute shells that have a quadrangular cross section in which the venter is much narrower that the dorsum, the venereal and umbilical shoulders usually angular, the flanks flattened and converging on the venter. Sutures form lobes on the sides and venter but are transverse across the dorsum. The siphuncle is tubular, orthochoanitic, and close to but not on the ventral margin. It includes some six genera.

The Grypoceratidae, predominant stock, established by Hyatt in 1900, are characterized by generally smooth, compressed, evolute to involute shells with the venter flattened to subangular. Ornamenation is not common, but some forms bear nodes or keels. Sutures have distinct ventral and lateral lobes. The siphuncle, which is narrow and tubular, is variable in position. It includes about 13 genera.

Shimanskiy separated the Domatoceratidae, typified by the Permian Domatoceras, from the Grypoceratidae in the Treatise,^[1] leaving the Grypoceratidae for mostly earlier forms.

The Permoceratidae, Permian offshoots named by Miller and Collinson in 1953 for the genus Permoceras, are involute, smooth, with a compressed, higher than wide, whorl section, ventrally subcentral siphuncle, and a suture with a deep, narrow, pointed ventral lobe and large pointed lateral lobes, mimicking contemporary goniatites.

The Syringonautilidae, Triassic offshoots named by Johann August Georg Edmund Mojsisovics von Mojsvar, 1902, gave rise to the Nautilaceae (Nautilina); containing five genera, they have generally smooth, involute shells with slightly sinuous sutures and a variably positioned siphuncle.

Discover more about Classification and phylogeny related topics

Alpheus Hyatt

Alpheus Hyatt

Alpheus Hyatt was an American zoologist and palaeontologist.

Centroceratidae

Centroceratidae

The Centroceratidae is the ancestral family of the Trigonoceratoidea and of the equivalent Centroceratina; extinct shelled cephalopods belonging to the order Nautilida

Grypoceratidae

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.

Mississippian (geology)

Mississippian (geology)

The Mississippian is a subperiod in the geologic timescale or a subsystem of the geologic record. It is the earlier of two subperiods of the Carboniferous period lasting from roughly 358.9 to 323.2 million years ago. As with most other geochronologic units, the rock beds that define the Mississippian are well identified, but the exact start and end dates are uncertain by a few million years. The Mississippian is so named because rocks with this age are exposed in the Mississippi Valley.

Cisuralian

Cisuralian

The Cisuralian is the first series/epoch of the Permian. The Cisuralian was preceded by the Pennsylvanian and followed by the Guadalupian. The Cisuralian Epoch is named after the western slopes of the Ural Mountains in Russia and Kazakhstan and dates between 298.9 ± 0.15 – 272.3 ± 0.5 Mya.

Evolute

Evolute

In the differential geometry of curves, the evolute of a curve is the locus of all its centers of curvature. That is to say that when the center of curvature of each point on a curve is drawn, the resultant shape will be the evolute of that curve. The evolute of a circle is therefore a single point at its center. Equivalently, an evolute is the envelope of the normals to a curve.

Subquadrate

Subquadrate

Lira (mollusc)

Lira (mollusc)

Lirae are fine lines or ridges that are a sculptural feature of the outside of the shells of various animals. The term is commonly applied to the shells of molluscs such as gastropods, bivalves and nautiloids. It can also be used to describe similar sculpture on the surface of the shells of brachiopods.

Siphuncle

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 Spirula. In the case of the cuttlefish, the siphuncle is indistinct and connects all the small chambers of that animal's highly modified shell; in the other cephalopods it is thread-like and passes through small openings in the septa (walls) dividing the camerae (chambers). Some older studies have used the term siphon for the siphuncle, though this naming convention is uncommon in modern studies to prevent confusion with a mollusc organ of the same name.

Involute

Involute

In mathematics, an involute is a particular type of curve that is dependent on another shape or curve. An involute of a curve is the locus of a point on a piece of taut string as the string is either unwrapped from or wrapped around the curve.

Domatoceras

Domatoceras

Domatoceras is a nautiloid genus and member of the Grypoceratidae from the Pennsylvanian and Permian with a wide spread distribution.

Permoceras

Permoceras

Permoceras, the sole member of the family Permoceratidae, is a genus of coiled nautiloids with a smooth, compressed involute shell, whorls higher than wide, earlier whorls hidden from view. The venter is rounded as are the ventral and umbilical shoulders, the flanks flattened. The siphuncle is ventrally subcentral. The suture, which is most characteristic, has a deep, narrow pointed ventral lobe and large, asymmetrical pointed lobes on either side.