Nautiloids - Classification

Classification

Classifications vary and a subject to change as new information is found and in accordance with the perspective of various workers. The taxonomy of the Taxo Box is one such scheme, Teichert's 1988 classification is another, that of Teichert et al. 1964 in the Treatise Part K, still another.

Wade (1988) divided the subclass Nautiloidea into 6 superorders, combing orders that are phylogenetically related. They are:

• Plectronoceratoidea = Plectronocerida, Protactinocerida, Yanhecerida,and Ellesmerocerida.
• Endoceratoidea = Endocerida
• Orthoceratoidea = Orthocerida, Ascocerida, and Pseudorthocerida (the Orthoceratoidea of Kröger 1007)
• Nautilitoidea = Tarphycerida, Oncocerida, and Nautilida.
• Actinoceratoidea = Actinocerida
• Discosoritoidea = Discosorida

Three of them are established as equivalent places to put Endocerida, Actinocerida, and Discosorida. Three unite related orders that share a common ancestor and form a branch of the nautiloid taxonomic tree; Plectronoceratoidea, which consists mostly of small Cambrian forms that include the ancestors of subsequent stocks; Orthoceratoidea, which unites different primarily orthoconic orders of which one is the source for Bacritida and Ammonoidea; and Nautilitoidea, which includes the first coilded cephalopods, Tarphycerida, as well as Nautilida, which includes the recent Nautilus.

Another order, Bactritida, which is derived from Orthocerida, is sometimes included with Nautiloidea, sometimes with Ammonoidea, and sometimes placed in a subclass of its own, Bactritoidea.

Recently some workers in the field have come to recognize Dissidocerida as a distinct order, along with Pseudorthocerida, both previously included in Orthoceridaas subtaxa.

A more recent interpretation (Engeser 1997-1998) suggests that nautiloids, and indeed cephalopods in general, fall into two main groups, Palcephalopoda (including all the nautiloids except Orthocerida and Ascocerida) and Neocephalopoda (the rest of the cephalopods).