Shevyrev (2006). Wade (1988) divided the subclass Nautiloidea (sensu lato) into 6 superorders, incorporating orders that are phylogenetically related. They are: †Plectronoceratoidea = †Plectronocerida, †Protactinocerida, †Yanhecerida, and †Ellesmerocerida. †Endoceratoidea = †Endocerida †Orthoceratoidea = †Orthocerida, †Ascocerida, and †Pseudorthocerida (the Orthoceratoidea of Kröger 2007) Nautilitoidea = †Tarphycerida, †Oncocerida, and Nautilida. †Actinoceratoidea = †Actinocerida †Discosoritoidea = †Discosorida Three of these superorders were established for orders of uncertain placement: Endocerida, Actinocerida, and Discosorida. The other three unite related orders which 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 (including the ancestors for Bacritida and Ammonoidea); and Nautilitoidea, which includes the first coiled 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 Orthocerida as subtaxa. Early cladistic efforts Cladistic approaches are rare in nautiloid systematics. Many nautiloid orders (not to mention the group as a whole) are not monophyletic clades, but rather paraphyletic grades. This means that they include some descendant taxa while excluding others. For example, the paraphyletic order Orthocerida includes numerous orthocerids stretching through the Paleozoic, but it excludes coleoids, despite coleoids having a well-established ancestry among the orthocerids. Interpretations by Engeser (1996-1998) suggests that nautiloids, and indeed cephalopods in general, should be split into two main clades: Palcephalopoda (including all the nautiloids except Orthocerida and Ascocerida) and Neocephalopoda (the rest of the cephalopods). Palcephalopoda is meant to correspond to groups which are closer to living nautilus, while Neocephalopoda is meant to correspond to groups closer to living coleoids. One issue which this scheme is the necessity of establishing a firm ancestry for nautilus, to contextualize which cephalopods are closer to which of the two living end members. On the basis of morphological traits, Nautilida is most similar to coiled early nautiloids such as the Tarphycerida and Oncocerida. However, these orders diverged from coleoid ancestors in the early Ordovician at the latest, while genetic divergence estimates suggest that Nautilida diverged in the Silurian or Devonian. A more recent phylogenetic study by Lindgren et al. (2004), which