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-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.

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.

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.

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.