Ammonoids are extinct spiral shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living coleoids than they are to shelled nautiloids. The earliest ammonoids appeared during the Devonian, with the last species vanishing during or soon after the Cretaceous–Paleogene extinction event. They are often called ammonites, which is most frequently used for members of the order Ammonitida, the only remaining group of ammonoids from the Jurassic up until their extinction.
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.
Goniatids, informally goniatites, are ammonoid cephalopods that form the order Goniatitida, derived from the more primitive Agoniatitida during the Middle Devonian some 390 million years ago. Goniatites (goniatitids) survived the Late Devonian extinction to flourish during the Carboniferous and Permian only to become extinct at the end of the Permian some 139 million years later.
In anatomy, a suture is a fairly rigid joint between two or more hard elements of an organism, with or without significant overlap of the elements.
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.
Lytoceratina is a suborder of Jurassic and Cretaceous ammonites that produced loosely coiled, evolute and gyroconic shells in which the sutural element are said to have complex moss-like endings.
Pseudohaloritidae is the larger of two families that form the goniatitid superfamily Pseudohaloritoidea, the other being the monogenerc Maximitidae. They are part of the vast array of shelled cephalopods known as ammonoids that are more closely related to squids, belemnites, octopuses, and cuttlefish, than to the superficially similar Nautilus.
Ussurites is an extinct ammonoid cephalopod genus belonging to the suborder Phylloceratina and is included in the family Ussuritidae. Its range is restricted to the early Middle Triassic, (Anisian)
Psiloceratoidea is a superfamily of Early Jurassic ammonoid cephalopods proposed by Hyatt in 1867, assigned to the order Ammonitida. They were very successful during Hettangian and Sinemurian. Last of them, family Cymbitidae and genera Hypoxynoticeras and Radstockiceras survived into Early Pliensbachian.
Prolecanitida is an order of extinct ammonoid cephalopods, the major Late Paleozoic group of ammonoids alongside the order Goniatitida. Prolecanitids had narrow shells, discoidal (disc-shaped) to thinly lenticular (lens-shaped). They retained a retrochoanitic siphuncle, a simple form with septal necks extending backwards. As is typical for ammonoids, the siphuncle sits along the ventral margin of the shell.
The Clydonautiloidea are a superfamily within the nautiloid order Nautilida characterized by smooth, generally globular, shells with nearly straight sutures, in early forms, but developing highly differentiated sutures in some later forms. Where known, the siphuncle tends to be central to subcentral.
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.
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 Cenozoic right down to the recent. Syringonautilidae is a strictly Triassic family, derived early in the Triassic from 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.
Phylloceratidae is the predominant family of the Phylloceratina with some 15 or more genera found in rocks ranging from the Lower Jurassic to the Upper Cretaceous. Members of the Phylloceratidae are characterized by smooth, involute shells with very thin walls. Many are covered with fine growth lines but are usually without ribbing. Sutures are complex with the major and minor branches of the saddles with phylloid or spatulate endings.
Discophyllitidae are discoidal, generally evolute Phylloceratina from the Upper Triassic, derived from the Ussuritidae, in which the principal saddles of the suture have bifurcated or trifurcated endings, described as being di- or triphyllic. Discophyllitid shells are rather similar to those of the ancestral Ussuritidae and are distinguished primarily by the more complex suture. The Discophyllitidae provided the source for the Jurassic Phylloceratidae and Juraphyllitidae. Four genera are recognized and described.
Gaza superba, common name the superb gaza, is a species of deep sea sea snail, a marine gastropod mollusc in the family Margaritidae.
The Clydonautilidae are Middle and Upper Triassic nautiloid cephalopods, which are derivatives of the clydonautiloidean family Liroceratidae, that have generally smooth, involute, globular to compressed shells, characterized by a suture with prominent lobes and saddles. The family is known to contain five genera, These are:
Tornoceras is a strongly involute, subdiscoidal Middle and Upper Devonian goniatite with a suture that forms six to ten lobes. Tornoceras is an extinct genus of cephalopods that shares similarities with the modern pearly nautilus. This genus first appeared during the Devonian Period, which spanned from 416 million to 359 million years ago. The shell is circular and relatively flat, with the final whorl enveloping the previous ones. The sutures between the successive chambers of the shell exhibit a gently rippled pattern.
Flickiidae is a family of dwarf ammonites with little ornament and very simples sutures known from small pyritic specimens found in middle Cretaceous deposits. Inclusion in the Acanthoceratoidea is tentative.
