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-spiraled, gyroconic, to closed, nautiliconic shells in which the Whorl section is quadrate in primitive forms; the venter 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.
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.
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.