Ammonitida is an order of more highly evolved ammonoid cephalopods that lived from the Jurassic through Cretaceous time periods, commonly with intricate ammonitic sutures.
Frechiella is an ammonite with a smooth, somewhat globose involute shell that lived during the later part of the Early Jurassic, which has been found in England and Italy. The shell is coiled so that the outer whorls cover most of the inner, leaving the inner whorls only slightly exposed. The outer rim, known as the venter, is broadly arched, with either a low narrow keel bordered by small grooves, or a large median groove.
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.
Stephanoceratoidea, formerly Stephanocerataceae, is a superfamily of middle- upper Jurassic ammonoid cephalopods within the order Ammonitida containing diverse forms, generally with sharp ribbing and complex suture lines. Aptychi are believed to be mostly granular (Granulaptycus) or concentrially ribbed on the surface (Praestriaptychus)
Otoidtidae: stephanoceratoid ammonitina from the early Middle Jurassic that begin as cadicones but become more planualte with age; derived from the Hammitoceratidae (Hildoceratoidea), probably through Erycites by way of Abbasites.
Eoderoceratoidea is a superfamily of true ammonites from the Lower Jurassic, comprising seven phylogenetically related families, characterized in general by having ribbed evolute shells that commonly bear spines or tubercles. Adult shell size ranges from 2 or 3 cm to giants reaching 50 cm in such genera as Apoderoceras, Epideroceras, and Liparoceras.
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.
Oppeliidae are compressed to oxyconic, sculptured Haploceratoidea, either unkeeled, unicarinate, bicarinate, or tricarinate; with sutures in great variety, but ribbing usually more or less falcoid or falcate. The Oppeliidae is the principal family of the Haploceratoidea, with the longest duration, extending from the Middle Jurassic (Bajocian) to the Upper Cretaceous (Cenomanian) Their derivation is from the Hildoceratoidea.
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.
Hammatoceratoidea, formerly Hammatocerataceae was a superfamily of middle Jurassic ammonites erected by Schindewolf in 1964 that combined the families Graphoceratidae, Hammatoceratidae, and Sonniniidae. The three families were previously included in the Hildoceratoidea, however subsequent classifications have moved the families back into Hildoceratoidea.
Harpoceratinae is an extinct subfamily of cephalopods belonging to the family Hildoceratidae. Ammonites of this subfamily had involute and compressed shells with strong keels. Keel might be rarely missing, but this is considered to be an abnormality. This has been observed both in Cleviceras and Harpoceras and called as genus Monestieria, which is now known to be invalid. Another example is Pseudolioceras, whose unkeeled specimen was used as type for description of invalid genus Praehaploceras. Oxyconic forms of this subfamily does not have any keel. Ribs were single, but in some genera also bifurcating with shapes from sigmoidal to falcate. Sometimes, shell can have only striate ribs or is smooth. Tubercules are rare. Dimorphism is known in some genera and it is observable mostly in size. Macrochons can be 4, to 6 times larger than microconchs. As an example, macroconchs of Pseudolioceras are more than 150mm in diameter, while adult microconchs are only 35-50mm. There are big size differences even within dimorphs. Specimens ca be 2, or sometimes even 3 times bigger than other specimens of same dimorph.
Erycitidae is a family of Lower and Middle Jurassic ammonites included in the Hildoceratoidea. The hammatoceratid subfamily Erycitinae is equivalent. Genera include Erycites (type) and Abbasites.
Hammatoceratidae is a family of lower and middle Jurassic ammonites included in the superfamily Hildoceratoidea.
Hammatoceras is a genus of ammonites belonging to the family Hammatoceratidae which lived during the Late Toarcian stage of the Early/Lower Jurassic between about 184 and 175 million year ago.
Collina is genus of ammonite that lived during lower to upper Toarcian stage of early Jurassic. Members of this genus existed from Braunianus Subzone to Variabilis Zone. Their fossils were found in Europe, Asia, North America and South America. It has evolved from Mesodactylites.
Hildoceratinae is an extinct subfamily of cephalopods belonging to the family Hildoceratidae. Ammonites of this subfamily had shells with elliptical or quadrate whorl section with keel or tricarinate, bisulcate venter. Ribs were variable, from falcate to strongly angled and from fine to strong. They can be interrupted by spiral groove in midlateral part of the shell. While some species can be smooth, strongly ribbed ones can have tubercules. Microconchs have short lapplets that is in its shape similar to the shape of growth lines in spiral midlateral groove.
Orthildaites is a genus of ammonites that lived during the lower Toarcian stage of early Jurassic, during Falciferum subzone.
Tiltoniceras is an extinct genus of cephalopod belonging to the family Hildoceratidae. These cephalopods existed in the Jurassic period, from upper Pliensbachian age, Spinatum zone until lower Toarcian, Tenuicostatum zone in what is now Europe, North America and Asian part of Russia.
Mercaticeras is an extinct genus of ammonites belonging to the family Hildoceratidae.
Federico Venturi was an Italian paleontologist. He is internationally known as a specialist of Early Jurassic ammonites.
