Editing Vetulicolia (section)

===History of identification===
[[File:Ou et al. 2012 f06.jpg|thumb|Evidence for the presence of a pharynx and dorsal/ventral feeding gutters in vetulicolians, supporting their placement among the [[Deuterostomes]].  Click through for detailed description.]]
The current consensus view is that vetulicolians are [[stem group]] [[chordates]], although some researchers continue to raise other possibilities.<ref name=Onai2023 />  The possible identification of an [[endostyle]] bolstered theories of a [[tunicate]] affinity, but was later retracted, while the tentative identification of a [[notochord]] in ''[[Nesonektris]]'' and ''[[Vetulicola]]'' has further supported overall chordate affinities.<ref name=Gee2018 /><ref name="GB2014" /> Other characters that have been used to support a tunicate affinity include the limiting of the notochord to the tail and the presence of a stiff cuticle (tunic).<ref name="GB2014" />

Recent research has strengthened the arguments for placing vetulicolians in the chordate stem lineage rather than near the tunicates.  Like vetulicolians, members of the [[basal (phylogenetics)|basal]] [[ambulacrarian]] clade [[Cambroernida]] have a terminal anus rather than a post-anal tail.  Since Ambulacraria is the sister-group of the chordates within the deuterostomes, this suggests that the last common ancestor of both groups lacked a post-anal tail.<ref name=ancestral /> However, ascidian larvae have been noted to have endoderm extending to the terminal end, which could suggest that tunicates also lacked post-anal tails ancestrally.<ref name="GB2014" />

Some workers have questioned the inclusion of Banffozoa within this group due to their lack of gill slits and apparent gut diverticula, and have theorized that they may fit within Protostomia instead.<ref name=Caron2005>{{harvnb|Caron|2005}}</ref> ''[[Skeemella]]'', in particular, has been noted as having striking arthropod-like characteristics.<ref>{{harvnb|Shu|2005|page=2352}}</ref> However, ''[[Herpetogaster]]'', the most basal cambroernid, is thought to have non-serialized pores for pharyngial openings.  If banffozoans are the most basal vetulicolians, this could explain why they also lack serialized pharyngeal structures.<ref name=ancestral /> Additionally, a comprehensive review of the Vetulicolia in 2007 did not find evidence of gut diverticula in their material while acknowledging the previous report regarding ''Banffia''.<ref>{{harvnb|Aldridge|Hou|Siveter|Siveter|2007|pages=151–152}}</ref>  ''[[Shenzianyuloma]]'' has been interpreted as a vetulicolian with both a notochord (a definitively deuterostome trait) and gut diverticula. However, this fossil has is of unusual provenance (a "crystal and fossil vendor"), and has not yet been examined by other researchers.<ref>{{harvnb|McMenamin|2019|pages=15–16}}</ref>

{{thumb|width=450|content=<div style="text-align:left;">
</div>
{{Clade|style=font-size:75%;line-height:75%
   |label1=Protostomia
   |1={{Clade
      |1=[[Spiralia]]
      |label2=[[Ecdysozoa]]
      |2={{Clade
         |label1=[[Kinorhyncha]]
         |sublabel1={{small|([[total group]])}}
         |1={{Clade
            |label1=
            |1=? Vetulicolia† |state1=dashed
            |2=[[Kinorhyncha]]<br />{{small|([[crown group]])}}
         }}
         |label2=[[Panarthropoda]]
         |2={{Clade
            |label1=
            |1=? Vetulicolia† |state1=dashed
            |2={{Clade
               |1=[[Onychophora]]
               |2={{Clade
                  |1={{Clade
                     |label1=
                     |1=? Vetulicolia† |state1=dashed
                     |2=[[Anomalocaridid|Anomalocaridida]]†
                  }}
                  |label2=[[Arthropoda]]
                  |sublabel2={{small|([[total group]])}}
                  |2={{Clade
                     |label1=
                     |1=? Vetulicolia† |state1=dashed
                     |2=[[Arthropoda]]<br />{{small|([[crown group]])}}
                  }}
               }}
            }}
         }}
      }}
   }}
   |label2=[[Deuterostomia]]
   |2={{Clade
      |1=? Vetulicolia† |state1=dashed
      |2={{Clade
         |label1=[[Ambulacraria]]
         |1={{Clade
            |1=? Vetulicolia† |state1=dashed
            |2={{Clade
               |1=[[Hemichordata]]
               |label2=[[Echinodermata]]
               |sublabel2={{small|([[total group]])}}
               |2={{Clade
                  |label1=
                  |1=? Vetulicolia† |state1=dashed
                  |2=[[Echinodermata]]<br />{{small|([[crown group]])}}
               }}
            }}
         }}
         |label2=[[Chordata]]
         |2={{Clade
            |1=? Vetulicolia† |state1=dashed
            |2={{Clade
               |label1=[[Tunicata]]
               |sublabel1={{small|([[total group]])}}
               |1={{Clade
                  |label1=
                  |1=? Vetulicolia† |state1=dashed
                  |2=[[Tunicata]]<br />{{small|([[crown group]])}}
               }}
               |label2=[[Euchordata]]
               |sublabel2={{small|([[total group]])}}
               |2={{Clade
                  |label1=
                  |1=? Vetulicolia† |state1=dashed
                  |label2=[[Euchordata]]
                  |sublabel2={{small|([[crown group]])}}
                  |2={{Clade
                     |1=[[Cephalochordata]]
                     |2=[[Vertebrata]]
                  }}
               }}
            }}        
         }}
      }}
   }}
}}
|caption=Adapted from cladograms in Aldridge ''et al.'' 2007, showing each possible placement for Vetulicolia considered in the paper;<ref>{{harvnb|Aldridge|Hou|Siveter|Siveter|2007|pages=156, 158}}</ref> note the presence of the [[Euchordata]] clade rather than the now-favored [[Olfactores]].
}}

Vetulicolians were thought to be stem [[arthropods]] when ''[[Vetulicola]]'' was first discovered, but around 2001 the focus of most theories shifted towards stem [[deuterostomes]] due to the discovery of pharyngial gill slits (a deuterostome characteristic), as well as the mounting evidence that vetuicolians have no appendages of any kind.<ref name=TreeOfLife>{{harvnb|Giribet|Edgecombe|2020|page=105}}</ref>  A theory grouping both vetulicolians and [[vetulocystida|vetulocystids]] with ''[[Saccorhytus]]'' was disproven when the alleged pharyngial openings of ''[[Saccorhytus]]'' were shown to be remnants of spines that had broken off; the saccorhytids are now considered to be [[ecdysozoans]].<ref>{{harvnb|Liu|Carlisle|Zhang|Yang|2022}}</ref>