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In a broad sense, "nautiloid" refers to a major cephalopod subclass or collection of subclasses (Nautiloidea sensu lato). 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).
The idea that the Nautilida evolved from straight-shelled ("Orthoceras") nautiloids, as proposed by Otto Schindewolf in 1942, through transitional forms such as the Ordovician Lituites can be rejected out of hand as evolutionarily unlikely. Lituites and the Lituitidae are derived tarphycerids and belong to a separate evolutionary branch of ...
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 ...
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This list of nautiloids is a comprehensive listing of all genera that have ever been included in the subclass Nautiloidea, excluding purely vernacular terms.The list includes all commonly accepted genera, but also genera that are now considered invalid, doubtful (nomina dubia), or were not formally published (nomina nuda), as well as junior synonyms of more established names, and genera that ...
An orthocone, loosely, may be thought of as a nautiloid shell, albeit somewhat larger and with a cone-shaped, straight formation as opposed to the nautiloid's coiled, curled shape. It was previously believed that these represented the most primitive form of nautiloid, however, it is now known that the earliest nautiloids had shells that were ...
Wade, M. 1988. Nautiloids and their descendants: cephalopod classification in 1986. Memoir 44, pp 15–25; New Mexico Bureau of Mines and Mineral Resources, Socorro, NM See also. Kummel Bernhard. Nautiloidea - Nautilida, Treatise on Invertebrate Paleontology Part K. Geological Soc of America and Univ of Kansas Press, R.C. Moore (Ed) 1964.
Cenoceras, the earliest member of the Nautilaceae and Nautilidae, is the only nautiloid known to have crossed the upper Triassic boundary and the only one known from the Lower Jurassic. All six families of the Nautilaceae, except for the Aturiidae ( Aturia ), are derived from the Cenoceras complex in the Middle Jurassic or from Eutrephoceras ...