Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids than they are to shelled nautiloids such as the living Nautilus species. The earliest ammonites appeared during the Devonian, with the last species vanishing during or soon after the Cretaceous–Paleogene extinction event.
Ammonitida is an order of ammonoid cephalopods that lived from the Jurassic through Paleocene time periods, commonly with intricate ammonitic sutures.
Abrytasites (Abrytusites) is an extinct genus of cephalopods belonging to the Ammonoidea subclass. The genus was named after the ancient Roman town of Abrittus, located near the present Bulgarian city of Razgrad. There are several described species of Abrytasites, including A. thieuloyi, A. julianyi, and A. neumayri. They are inflated, with constrictions, have rather thick ribs springing irregularly, singly or in pairs, from umbilical bullae. Their inner whorls closely resemble types species of Valdedorsella. This animal lived 125–136.4 million years ago during the Hauterivian and the Barremian in Europe and western Africa.
Australiceras is an extinct ammonite genus from the upper part of the Early Cretaceous, Aptian stage, included in the family Ancyloceratidae.
Anagaudryceras is an extinct genus of ammonite from the later Cretaceous belonging to the Ammonoidea family Gaudryceratidae. Anagaudryceras has a moderately involute shell with a deep umbilicus and strongly ribbed outer whorl. Ribs are thick and rounded and cross over the venter uninterrupted.
Asapholytoceras is a lytoceratid ammonite, originally from the upper Lower Jurassic of southeastern Europe with high, compressed whorls and a sharp angle to the umbilical shoulder. The exposed suture has four primary lobes on either side; the internal dorsal lobe is not cruciform.
Aulatornoceras is a genus belonging to the subfamily Aulatornoceratinae, a member of the Goniatitida, an extinct order of shelled cephalopods included in the Ammonoidea. Aulatornoceras, which has been considered a subgenus of Tornoceras has ventro-lateral grooves. As with Tornoceras, the suture forms six lobes. The shell itself is involute.
Barremites is an ammonoid cephalopod genus belonging to the family Desmoceratidae, that lived during the Hauterivian and Barremian stages of the Early Cretaceous.
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.
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.
Heteroceras is a genus of Lower Cretaceous heteromorph ammonites belonging to the ancyloceratoidean family, Heteroceratidae.
Tissotiidae is a family of ammonites (Ammonitina) belonging to the Acanthoceratoidea.
Acanthoceratoidea, formerly Acanthocerataceae, is a superfamily of Upper Cretaceous ammonoid cephalopods belonging to the order Ammonitida, and comprising some 10 or so families.
Arietitidae is a family of true ammonites that make up part of the superfamily Psiloceratoidea, named after the type genus Arietites. They comprise medium-size to large or gigantic genera which in general are strongly ribbed, tuberculate in some, with keeled or grooved and keeled venters, and well differentiated ammonitic sutures. The aptycus is single valved with a shiny, concentrically striated surface.
Desmoceratoidea, formerly Desmocerataceae, is a superfamily of Cretaceous ammonites, generally with round or oval-whorled shells that are mostly smooth or weakly ribbed and rarely tuberculate, but commonly with constrictions. Regarded as monophyletic, the Desmocerataceae are derived from the Phylloceratidae, splitting off in the Early Cretaceous (Valanginian) and persisting to the end of the Maastrichtian.
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.
Perisphinctidae is a family of Middle and Upper Jurassic discoidal ammonites in the order Ammonitida. They have a shell morphology that is mostly evolute, typically with biplicate, simple, or triplicate ribbing. Large forms have simple apertures and smooth body chambers while small forms have lappets and ribbed body chambers.
Lytoceratidae is a taxonomic family of ammonoid cephalopods belonging to the suborder Lytoceratina, characterized by very evolute shells that generally enlarge rapidly, having whorls in contact but mostly overlapping very sightly, or not at all.
Megalytoceras is an extinct genus of ammonite from the middle Jurassic, belonging to the suborder Lytoceratina.
Holcodiscus is an extinct ammonite genus placed in the family Holcodiscidae. Species in this genus were fast-moving nektonic carnivores. The type species of the genus is Ammonites caillaudianus.
