The Ancyloceratina were a diverse suborder of ammonite most closely related to the ammonites of order Lytoceratina. They evolved during the Late Jurassic but were not very common until the Cretaceous period, when they rapidly diversified and became one of the most distinctive components of Cretaceous marine faunas. They have been recorded from every continent and many are used as zonal or index fossils. The most distinctive feature of the majority of the Ancyloceratina is the tendency for most of them to have shells that are not regular spirals like most other ammonites. These irregularly-coiled ammonites are called heteromorph ammonites, in contrast to regularly coiled ammonites, which are called homomorph ammonites.
Australiceras is an extinct ammonite genus from the upper part of the Early Cretaceous, Aptian stage, included in the family Ancyloceratidae.
Algerites is middle Cretaceous (Cenomanian) anisoceratid ammonoid with a close-coiled adult shell in which the whorls at that stage are in close contact, after starting off with openly coiled whorls, and in which every rib has a pair of sharp ventral tubercles.
Ancyloceras is an extinct genus of heteromorph ammonites found throughout the world during the Lower Cretaceous, from the Lower Barremian epoch until the genus extinction during the Lower Aptian.
Anaklinoceras is a genus of extinct heteromorph ammonite cephalopod that lived in marine environments in what is now Western North America during the Campanian division of the Cretaceous period. Their shells were very similar to the related ammonites of the genus Ainoceras, where the young ammonite's shell coiled helically, and upon reaching adulthood, the youngest coil arched over the older coils.
Axonoceras is a genus in the ammonitid family Nostoceratidae proposed by Stephenson in 1941, for "slender shells coiled in a plane with numerous closely spaced ribs and two rows of ventral nodes'...The shells may be closely coiled, though not involute, but most... are more or less loosely and irregularly coiled". Shells may be coplanar or coiled in a low flat spiral with the early whorls in contact, later whorls free.
Astiericeras is an ammonite from the Lower Cretaceous, the shell of which is evolute, stout; outer whorl with strong, well spaced, transverse ribs that cross smoothly over the broad venter; early whorls with lateral tubercles. The outer, mature whorl separates from the coil but hooks back quickly, referred to as a heteromorph.
Parapuzosia is an extinct genus of desmoceratid ammonites from the Cenomanian to the Campanian of Africa, Europe, and North America. They are typically very large ammonites, reaching diameters of 60 cm (2.0 ft) or more, with the largest species measuring upwards of more than 2.5 m (8.2 ft). It possesses a moderately involute shell with flat or slightly rounded sides. Distinct primary and secondary ribbing can be observed in the inner whorls.
The columella or pillar is a central anatomical feature of a coiled snail shell, a gastropod shell. The columella is often only clearly visible as a structure when the shell is broken, sliced in half vertically, or viewed as an X-ray image.
Nostoceratidae is a diverse family of heteromorph ammonites found throughout the oceans of the world during the Late Cretaceous. The nostoceratids are famous for the bizarre coiling of their shells. Many genera, such as Yezoceras, Ainoceras, Anaklinoceras, and some species of Bostrychoceras and Eubostrychoceras, display, as young shells at least, a helical coiling very similar to the shells of the related family, Turrilitidae. As adults, though, the coils then curve away from the axis of coiling, either as an oxbow-like curve around the juvenile coils as in Ainoceras and Anaklinoceras, or in a simple curved loop beneath the juvenile coils, as in Yezoceras. Other genera form loose coils, sometimes in a spiral, such as those of Madagascarites, Muramotoceras, Hyphantoceras, and the infamously convolute Nipponites.
Bradfordia is a moderately involute to involute genus included in the ammonoid cephalopod family Oppeliidae, coiled so that the outer whorl encloses most, or much, of the previous, but with a small umbilicus exposing inner whorls. The shell is compressed, whorl height much greater than width, extending well out from the contact with the adjacent inner whorl. Outer flanks are finely ribbed and the rounded venter is smooth.
Parastrenoceras is an extinct genus from the ammonoid cephalopod order Ammonitida, included in the family Spiroceratidae that lived during the Bajocian stage of the Middle Jurassic.
Uranoceras is a barrandeocerid genus from the Middle Silurian belonging to the family Uranoceratidae, characterized by its loosely coiled, gyroconic shell of 1.5 to 2 subquadrate whorls.
Permoceras, the sole member of the family Permoceratidae, is a genus of coiled nautiloids with a smooth, compressed involute shell, whorls higher than wide, earlier whorls hidden from view. The venter is rounded as are the ventral and umbilical shoulders, the flanks flattened. The siphuncle is ventrally subcentral. The suture, which is most characteristic, has a deep, narrow pointed ventral lobe and large, asymmetrical pointed lobes on either side.
Tylonautilus is an extinct genus in the nautiloid order Nautilida from the Lower Carboniferous of Europe and Permian of Japan.
Trigonoceras is an extinct genus of prehistoric nautiloids from the nautilid family Trigonoceratidae that lived during the Early Carboniferous in what is now western Europe.
Clymeniida is an order of ammonoid cephalopods from the Upper Devonian characterized by having an unusual dorsal siphuncle. They measured about 4 cm (1.6 in) in diameter and are restricted to Europe, North Africa, and possibly Australia.
Eubostrychoceras is a genus of helically wound, corkscrew form, heteromorph ammonite which lived during the Upper Cretaceous. The genus is included in the ancycleratid family Nostoceratidae.
Macroscaphites is an extinct cephalopod genus included in the Ammonoidea that lived during the Barremian and Aptian stages of the Early Cretaceous. Its fossils have been found throughout most of Europe and North Africa.
Calycoceras is an extinct genus of cephalopods belonging to the subclass Ammonoidea and family Acanthoceratidae that lived during the Cenomanian stage of the Late Cretaceous, 100-94 Mya. Their shells had ornate ribs.
