Editing Nautiloid (section)

{{Short description|Extant subclass of cephalopods}}
{{Automatic taxobox
| name = Nautiloids
| fossil_range = {{fossil range|495|0}}[[Late Cambrian]] – Recent
| image = Nautilus-JB-01.jpg
| image_caption = ''[[Nautilus pompilius]]''
| image2 = Cameroceras trentonese.jpg
| image2_caption = the [[Endocerida|endocerid]] ''[[Cameroceras]]'', shown feeding on the [[Tarphycerida|tarphycerid]] ''[[Aphetoceras]]'', while a quartet of [[Ellesmerocerida|ellesmerocerid]] ''[[Cyclostomiceratidae|Cyclostomiceras]]'' swim by.
| taxon = Nautiloidea
| authority = [[Louis Agassiz|Agassiz]], 1847
| subdivision_ranks = Major subdivisions
| subdivision = *†[[Plectronoceratoidea]] <small>([[paraphyletic]])</small>
*†[[Endoceratoidea]]
*Order [[Nautilida]]
*†[[Multiceratoidea]] <small>( possibly paraphyletic)</small>
*†[[Orthoceratoidea]] <small>(paraphyletic)</small>
}}

'''Nautiloids''' are a group of [[cephalopod]]s ([[Mollusca]]) which originated in the [[Late Cambrian]] and are represented today by the living ''[[Nautilus (genus)|Nautilus]]'' and ''[[Allonautilus]]''. [[Fossil]] nautiloids are diverse and species rich, with over 2,500 recorded species. They flourished during the early [[Paleozoic]] era, when they constituted the main predatory animals. Early in their evolution, nautiloids developed an extraordinary diversity of shell shapes, including coiled morphologies and giant straight-shelled forms ([[orthocone]]s). No orthoconic and only a handful of coiled species, the [[nautilus]]es, survive to the present day.

In a broad sense, "nautiloid" refers to a major cephalopod [[Subclass (biology)|subclass]] or collection of subclasses ('''Nautiloidea ''sensu lato'''''). Nautiloids are typically considered one of three main groups of cephalopods, along with the extinct [[Ammonoidea|ammonoids]] (ammonites) and living [[Coleoidea|coleoids]] (such as [[squid]], [[octopus]], and kin). While ammonoids and coleoids are [[Monophyly|monophyletic]] [[clade]]s with exclusive ancestor-descendant relationships, this is not the case for nautiloids. Instead, nautiloids are a [[Paraphyly|paraphyletic]] [[Evolutionary grade|grade]] of various early-diverging cephalopod lineages, including the ancestors of ammonoids and coleoids. Some authors prefer a narrower definition of Nautiloidea ('''Nautiloidea ''sensu stricto'''''), as a singular subclass including only those cephalopods which are closer to living nautiluses than they are to either ammonoids or coleoids.