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 Allonautilus, with six species. All told, between 22 and 34 families and 165 to 184 genera have been recognised, making this the largest order of the subclass Nautiloidea.
Ammonitida is an order of more highly evolved ammonoid cephalopods that lived from the Jurassic through Cretaceous time periods, commonly with intricate ammonitic sutures.
Arctoceras is a genus of ceratitid ammonoids from the Lower Triassic with a moderately narrow discoidal shell and ceratitic suture.
Arctogymnites is a genus of ammonoid cephalopods from the middle Triassic included in the ceratitid subfamily Beyrichitinae. Related genera include Beyrichites, Frechites, Gymnotoceras, and Salterites
Badiotites is a genus of extinct ammonoid cephalopods belonging to the ceratitid family Badiotitidae. It was previously included with Lecanites in the Lecanitidae, a family formerly of the Clydonitaceae but reassigned by Tozer (1981) to the Danubitaceae. The Badiotitidae is included in the Ceratitaceae.
Ceratitida is an order that contains almost all ammonoid cephalopod genera from the Triassic as well as ancestral forms from the Upper Permian, the exception being the phylloceratids which gave rise to the great diversity of post Triassic ammonites.
'Xenodiscoidea, formerly Xenodiscaceae, is a superfamily within the ammonoid order Ceratitida. The superfamily was named by Frech in 1902, presently contains ten families, only one of which was included in the original Otocerataceae of Hyatt, 1900, the remaining having been added.
Ammonitina comprises a diverse suborder of ammonite cephalopods that lived during the Jurassic and Cretaceous periods of the Mesozoic Era. They are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific geological time periods.
Ancyloceratoidea, formerly Ancylocerataceae, is a superfamily of typically uncoiled and loosely coiled heteromorph ammonoids established by Alpheus Hyatt in 1900, that may contain as many as 11 families, depending on the classification accepted.
Ceratitoidea, formerly Ceratitaceae, is an ammonite superfamily in order Ceratitida characterized in general by highly ornamented or tuberculate shells with ceratitic sutures that may become goniatitic or ammonitic in some offshoots.
The Trachyceratidae is an extinct family of ceratitid ammonoid cephalopods.
The Tropitidae is a family of Upper Triassic Ammonoidea belonging to the Tropitaceae, a superfamily of the Ceratitida
The Danubitoidea is a large and diverse superfamily in the order Ceratitida of the Ammonoidea that combines five families removed from the Ceratitaceae, Clydonitaceae, and Ptychitaceae.
Paratirolites is a genus of Early Triassic ceratites from Armenia and Iran with distinct ribs, prominent ventro-lateral tubercles, and a broadly arched venter. The suture is ceratitic with a large ventral saddle. Ceratites are ammonoid cephalopods that lived during the Late Permian and Triassic.
Perisphinctoidea, formerly Perisphinctaceae, is a superfamily of Middle Jurassic (Bajocian) to Lower Cretaceous (Barremian) ammonites, commonly with evolute shells with strong ribbing that typically divides about mid flank before crossing the venter.
Gymnites is a genus of ammonoid cephalopod from the Middle Triassic belonging to the ceratitid family Gymnitidae. These nektonic carnivores lived during the Triassic period, Anisian age.
Gymnitidae is a family of Lower to Middle Triassic ammonite cephalopods with evolute, discoidal shells.
Hildoceratidae is a family of ammonoid cephalopods from the Lower Jurassic, lower Pliensbachian to lower Bajocian substages, generally with strongly ribbed, involute shells. They are combined with the Hammatoceratidae, Graphoceratidae, and Sonniniidae to make up the Hildoceratoidea.
Aplococeratidae is a family of ceratitids from the Middle Triassic with very simplified sutures and a tendency to lose their ornamentation. Shells are generally evolute, more or less compressed, with rounded venters. Ornamentation if present consists of umbilical ribs that disappear outwardly, toward the venter. The suture is ceratitic or goniatitic.
Protrachyceras is a genus of ceratitid ammonoid cephalopods belonging to the family Trachyceratidae.
