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A primary difference between ammonites and nautiloids is the siphuncle of ammonites (excepting Clymeniina) runs along the ventral periphery of the septa and camerae (i.e., the inner surface of the outer axis of the shell), while the siphuncle of nautiloids runs more or less through the center of the septa and camerae.
Nautiloids are typically considered one of three main groups of cephalopods, along with the extinct ammonoids (ammonites) and living coleoids (such as squid, octopus, and kin). While ammonoids and coleoids are monophyletic clades with exclusive ancestor-descendant relationships, this is not the case for nautiloids.
Nautiloids were much more extensive and varied 200 million years ago. The ancestors of all Coleoidea (shell-less Cephalopods) once possessed shells, and many early cephalopod species are only known from shell remains. Following the K-Pg extinction event most nautiloid species went extinct, while members of Coleoidea managed to survive ...
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 ...
Also acid ionization constant or acidity constant. A quantitative measure of the strength of an acid in solution expressed as an equilibrium constant for a chemical dissociation reaction in the context of acid-base reactions. It is often given as its base-10 cologarithm, p K a. acid–base extraction A chemical reaction in which chemical species are separated from other acids and bases. acid ...
Any shells with complex sutures were assigned to the genus Ammonites. This definition persisted for nearly 200 years, from the time of the genera's 1758 inception by Carl Linnaeus to 1949, when paleobiologist Arthur K. Miller provided a detailed description of the shell of N. pompilius, becoming the type species of the genus.
The main difference is that the Rutoceratidae are included with the Aipocerataceae of Kummel (1964) in the Rutoceratina. The remaining Tainocerataceae are the Tainoceratina. Rousseau Flower (1950) distinguished the Solenochilida, Rutoceratida, and Centroceratida, as separate orders, from the Nautilida, derived from the Barrandeocerida, which ...
Ammonites — members of the Ammonoidea subclass of molluscan prehistoric cephalopods. Pages in this category should be moved to subcategories where applicable. This category may require frequent maintenance to avoid becoming too large.