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This list of ammonites is a comprehensive listing of genera that are included in the subclass †Ammonoidea, excluding purely vernacular terms. The list includes genera that are commonly accepted as valid, as well as those that may be invalid or doubtful ( nomina dubia ), or were not formally published ( nomina nuda ), as well as junior ...
Fagesia is a small, subglobular ammonite (suborder Ammonitina) belonging to the vascoceratid family of the Acanthocerataceae that lived during the Turonian stage of the Late Cretaceous, 92–88 Ma ago.
Ammonites of prehistoric North America — a marine molluscs group of the prehistoric Cephalopods in North America. Subcategories This category has the following 5 subcategories, out of 5 total.
Sphenodiscus is an extinct genus of acanthoceratacean ammonite.The genus has been found from many continents and is thought to have had a large global distribution during the Maastrichtian stage of the Late Cretaceous.
Nostoceras is the type genus for the ammonite family Nostoceratidae which is included in the Turrilitoidea. [2] The Turrilitoidea, with Nostoceras and the Nostoceratidae, are commonly included in the suborder Ancyloceratina but may instead belong in the Turrilitina, a proposed order of heteromorphs thought to have a separate derivation, though this separation does not have wide support.
Ancyloceras ammonites have a shell reaching a length of about 10 centimetres (3.9 in) and a width of about 7 centimetres (2.8 in). They are known as heteromorph shaped, with a partly uncoiled shell and the aperture directed toward the coiled part.
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.
Polyptychoceras is a heteromorph ammonite, meaning that its shell does not curl up into the tight spiral shape which shells of ammonites from the subclass Ammonoidea typically do. Polyptychoceras shells have an abrupt weight increase after formation of the initial shaft, which represents the shell's automatic balance condition. [ 4 ]