Vicissicaudata

{{Short description|Extinct group of artiopods}} {{Automatic taxobox | fossil_range = {{fossil_range|Cambrian Stage 3|Moscovian|Early Cambrian - Late Carboniferous}} | image = Sidneyia minor.png | image_caption = ''Sidneyia minor'', a vicissicaudatan unplaced in any subgroup | image2 = 20200415_Cheloniellon_calmani.png | image2_caption = ''Cheloniellon'', a cheloniellid | taxon = Vicissicaudata | authority = Ortega-Hernández, Legg & Braddy, 2013 | subdivision_ranks = Subgroupings | subdivision = *†''Etainia'' *†''Kodymirus'' *†''Sidneyia'' *†''Emeraldella'' *†''Eozetetes'' *†''Tardisia''<ref name=tardisia>{{cite journal |last1=McCoy |first1=Victoria E. |last2=Herrera |first2=Fabiany |last3=Wittry |first3=Jack |last4=Mayer |first4=Paul |last5=Lamsdell |first5=James C. |title=A possible vicissicaudatan arthropod from the Late Carboniferous Mazon Creek Lagerstätte |journal=Geological Magazine |date=2025 |volume=162 |doi=10.1017/S001675682400044X|doi-access=free }}</ref> *†''Carimersa'' *†''Molaria''? *†''Acanthomeridion''? *†'''Cheloniellida''' *†'''Aglaspidida''' | synonyms = *Xenopoda Raymond, 1935 (in part) | subdivision_ref = }}

'''Vicissicaudata''' is an unranked group of artiopodan arthropods, containing Cheloniellida, the speciose Aglaspidida, and several other genera outside these groups like ''Sidneyia'' and ''Emeraldella.''

== Description ==

Vicissicaudatans are similar to most other artiopods in shape, with rounded bodies consisting of many wide tergites, sometimes with a distinguishable axis along the midline. This clade is defined by a differentiated posterior region,<ref name=Hernandez2013>{{cite journal |last1=Ortega‐Hernández |first1=Javier |last2=Legg |first2=David A. |last3=Braddy |first3=Simon J. |title=The phylogeny of aglaspidid arthropods and the internal relationships within Artiopoda |journal=Cladistics |date=February 2013 |volume=29 |issue=1 |pages=15–45 |doi=10.1111/j.1096-0031.2012.00413.x}}</ref> often ending in a telson and caudal appendages. The morphology of this posterior region varies between clades. Aglaspidids, alongside ''Eozetetes''<ref name=eozetetes>{{cite journal |last1=Edgecombe |first1=Gregory D. |last2=Paterson |first2=John R. |last3=García-Bellido |first3=Diego C. |title=A new aglaspidid-like euarthropod from the lower Cambrian Emu Bay Shale of South Australia |journal=Geological Magazine |date=January 2017 |volume=154 |issue=1 |pages=87–95 |doi=10.1017/s0016756815001053}}</ref> and ''Carimersa'',<ref name=carimersa>{{cite journal |last1=Briggs |first1=Derek E. G. |last2=Siveter |first2=David J. |last3=Siveter |first3=Derek J. |last4=Sutton |first4=Mark D. |last5=Legg |first5=David |last6=Lamsdell |first6=James C. |title=A vicissicaudatan arthropod from the Silurian Herefordshire Lagerstätte, UK |journal=Royal Society Open Science |date=August 2023 |volume=10 |issue=8 |doi=10.1098/rsos.230661 |doi-access=free|pmc=10394423 }}</ref> have long styliform telsons and relatively small, flap-like caudal appendages while cheloniellids and ''Tardisia'' have much longer caudal appendages similar to the caudal furcae of various taxa, alongside much smaller telsons more resembling the postabdominal segments. The paraphyletic "xenopods" are more similar to those of aglaspidids, also with long telsons and flap-like caudal appendages, however in ''Sidneyia''<ref name=sidneyia>{{cite journal |last1=Du |first1=Kunsheng |last2=Bruton |first2=David L. |last3=Yang |first3=Jie |last4=Zhang |first4=Xiguang |title=An early Cambrian Sidneyia (Arthropoda) resolves the century-long debate of its head organization |journal=Science China Earth Sciences |date=March 2023 |volume=66 |issue=3 |pages=521–527 |doi=10.1007/s11430-022-1019-8}}</ref> the caudal appendages have become large with broad, lobed tips. In terms of bodily morphology, aglaspidids and ''Carimersa'' closely resemble trilobites, with cheloniellids having an unusual radial arrangement of their tergopleurae. The various basal taxa are mostly less derived in body shape with rounded tergite edges and large head shields, although the first appendage pair of ''Kodymirus'' vaguely resembles the frontal appendages of radiodonts.<ref name=kodymirus>{{cite journal |last1=Lamsdell |first1=James C. |last2=Stein |first2=Martin |last3=Selden |first3=Paul A. |title=Kodymirus and the case for convergence of raptorial appendages in Cambrian arthropods |journal=Naturwissenschaften |date=September 2013 |volume=100 |issue=9 |pages=811–825 |doi=10.1007/s00114-013-1081-y}}</ref> Most have eyes, although some later aglaspidids and cheloniellids, alongside ''Tardisia'' and ''Etainia'',<ref name=etainia>{{cite journal |last1=Legg |first1=David A. |last2=Hearing |first2=Thomas W. |title=A late surviving xenopod (Arthropoda) from the Ordovican[''sic''] Period, Wales |journal=Geological Magazine |date=September 2015 |volume=152 |issue=5 |pages=942–948 |doi=10.1017/S001675681400065X}}</ref> seem to lack them. However, the placement of eyes varies throughout Vicissicaudata, with some having eyes on the underside of their carapace (such as ''Emeraldella''),<ref name=ebrocki/> so the apparent lack of eyes may simply be due to them not being visible on fossils. Unlike trilobites, most vicissicaudatans are not biomineralised, therefore they are much rarer and mainly appear in lagerstätten.

== Distribution ==

Vicissicaudatans seem to have a wide distribution both in time and space, with fossils being recorded from the Cambrian to the Carboniferous. Fossils have been found in locations including but not limited to the Burgess Shale,<ref name=ebrocki>{{cite journal |last1=Stein |first1=Martin |last2=Selden |first2=Paul A. |title=A restudy of the Burgess Shale (Cambrian) arthropod Emeraldella brocki and reassessment of its affinities |journal=Journal of Systematic Palaeontology |date=June 2012 |volume=10 |issue=2 |pages=361–383 |doi=10.1080/14772019.2011.566634}}</ref> Wheeler Shale,<ref name=ebrutoni>{{cite journal |last1=Stein |first1=Martin |last2=Church |first2=Stephen B. |last3=Robison |first3=Richard A. |title=A new Cambrian arthropod, Emeraldella brutoni, from Utah |journal=Paleontological Contributions |date=29 September 2011 |issue=3 |doi=10.17161/PC.1808.8086|hdl=1808/8086 |hdl-access=free }}</ref> Chengjiang biota,<ref name=sidneyia/> Paseky Shale,<ref name=kodymirus/> Emu Bay Shale,<ref name=eozetetes/> Fezouata Formation,<ref>{{cite journal |last1=Ortega-HernáNdez |first1=Javier |last2=Van Roy |first2=Peter |last3=Lerosey-Aubril |first3=Rudy |title=A new aglaspidid euarthropod with a six-segmented trunk from the Lower Ordovician Fezouata Konservat-Lagerstätte, Morocco |journal=Geological Magazine |date=May 2016 |volume=153 |issue=3 |pages=524–536 |doi=10.1017/S0016756815000710|hdl=1854/LU-8714213 |hdl-access=free }}</ref> Llanfallteg Formation,<ref name=etainia/> Coalbrookdale Formation,<ref name=carimersa/> Hunsrück Slate<ref>{{cite journal |last1=Stürmer |first1=Wilhelm |last2=Bergström |first2=Jan |title=The arthropod Cheloniellon from the devonian hunsrück shale |journal=Paläontologische Zeitschrift |date=June 1978 |volume=52 |issue=1-2 |pages=57–81 |doi=10.1007/BF03006730}}</ref> and Mazon Creek.<ref name=tardisia/>

== Taxonomy == ''Sidneyia'' and ''Emeraldella'' were recognised to be closely related to each other since the early 20th century, with the order "Xenopoda" being erected to house the two genera in 1935.<ref>Raymond, P. E. 1935. ''Leanchoilia'' and other Mid-Cambrian Arthropoda. Museum of Comparative Zoology Bulletin 76, 205–30.Google Scholar</ref><ref name="etainia" /> A close relationship between ''Sidneyia'', ''Emeraldella'', aglaspididans and cheloniellids had long been hypothesised, but the grouping lacked a formal name until 2013. Vicissicaudata is often considered to be closely related to the clade containing trilobites and their close relatives (Trilobitomorpha) as part of Artiopoda,<ref name=":0">{{Cite journal |last=Lerosey-Aubril |first=Rudy |last2=Zhu |first2=Xuejian |last3=Ortega-Hernández |first3=Javier |date=2017-09-11 |title=The Vicissicaudata revisited – insights from a new aglaspidid arthropod with caudal appendages from the Furongian of China |url=https://www.nature.com/articles/s41598-017-11610-5 |journal=Scientific Reports |language=en |volume=7 |issue=1 |doi=10.1038/s41598-017-11610-5 |issn=2045-2322 |pmc=5593897 |pmid=28894246}}</ref> though some studies hypothesise that Artiopoda is paraphyletic, with some studies hypothesising that Vicissicaudata is more closely related to other arthropod groups like chelicerates than to trilobitomorphs.<ref>{{Cite journal |last=Lustri |first=Lorenzo |last2=Antcliffe |first2=Jonathan B. |last3=Gueriau |first3=Pierre |last4=Daley |first4=Allison C. |date=October 2024 |title=New specimens of Bunaia woodwardi Clarke, 1919 (Euchelicerata): a new member of Offacolidae providing insight supporting the Arachnomorpha |url=https://royalsocietypublishing.org/doi/10.1098/rsos.240499 |journal=Royal Society Open Science |language=en |volume=11 |issue=10 |doi=10.1098/rsos.240499 |doi-access=free|issn=2054-5703 |pmc=11524597 |pmid=39479250}}</ref>

Cladogram after McCoy et al. 2025:<ref name="tardisia2">{{cite journal |last1=McCoy |first1=Victoria E. |last2=Herrera |first2=Fabiany |last3=Wittry |first3=Jack |last4=Mayer |first4=Paul |last5=Lamsdell |first5=James C. |date=2025 |title=A possible vicissicaudatan arthropod from the Late Carboniferous Mazon Creek Lagerstätte |journal=Geological Magazine |volume=162 |doi=10.1017/S001675682400044X|doi-access=free }}</ref>{{Clade|{{clade |label1=Vicissicaudata |1={{Clade sequential |1=''Molaria spinifera'' 70px |2=''Emeraldella brocki'' |3=''Emeraldella brutoni'' 100px |4={{Clade sequential |1=''Sidneyia inexpectans'' 100px |2=''Tardisia broedeae'' |3=Cheloniellida 150px }} |5=''Carimersa neptuni'' |6=''Kodymirus vagans'' 70px |7=''Eozetetes gemelli'' |8=Aglaspidida 100px }} }}|label1=}}

Cladogram after Lerosey-Aubril et al. (2017).<ref name=":0" /> {{clade |label1='''Vicissicaudata''' |1={{clade |1=''Sidneyia'' |2={{clade |label1=Cheloniellida|1={{clade |1=''Neostrabops'' |2={{clade |1=''Cheloniellon'' |2={{clade |1=''Triopus'' |2=''Duslia'' }} }} }} |2={{clade |1=''Emeraldella'' |2={{clade |1=''Kodymirus'' |2={{clade |1=''Eozetetes'' |2=Aglaspidida }} }} }} }} }} }} Cladogram after Jiao et al. 2021.<ref>{{Cite journal |last1=Jiao |first1=De-Guang |last2=Du |first2=Kun-Sheng |last3=Zhang |first3=Xi-Guang |last4=Yang |first4=Jie |last5=Eggink |first5=Daniel |date=May 2022 |title=A new small soft-bodied non-trilobite artiopod from the Cambrian Stage 4 Guanshan Biota |journal=Geological Magazine |language=en |volume=159 |issue=5 |pages=730–734 |doi=10.1017/S0016756821001254 |issn=0016-7568 |doi-access=free}}</ref>{{clade |label1='''Vicissicaudata''' |1={{clade |1=''Sidneyia inexpectans'' |2={{clade |1=''Emeraldella brocki'' |label2=Cheloniellida |2={{clade |1=''Cheloniellon calmani'' |2={{clade |1=''Triopus draboviensis'' |2=''Duslia insignis'' }} }} |3={{clade |1=''Kodymirus vagans'' |2={{clade |1=''Eozetetes gemmelli'' |label2=Aglaspidida |2={{clade |1=''Beckwithia typa'' |2={{clade |1={{clade |1=''Chlupacaris dubia'' |2={{clade |1=''Quasimodaspis brentsae'' |2={{clade |1=''Tremaglaspis unite'' |2={{clade |1=''Tremaglaspis vanroyi'' |2=''Brachyaglaspis singularis'' }} }} }} |3={{clade |1=''Cyclopites vulgaris'' |2=''Australaglaspis stonyensis'' |3={{clade |1=''Uarthrus instabilis'' |2=''Flobertia kochi'' |3={{clade |1=''Aglaspella granulifera'' |2={{clade |1=''Gogglops ensifer'' |2={{clade |1=''Glypharthrus simplex'' |2=''Aglaspis spinifer'' }} }} |3={{clade |1=''Chraspedops modesta'' |2={{clade |1=''Glypharthrus thomasi'' |2={{clade |1=''Glypharthrus trispinicaudatus'' |2=''Glypharthrus magnoculus'' }} }} }} }} }} }} }} }} }} }} }} }} }} }}

== Etymology == Vicissicaudata translates to "changed tail", in reference to the differentiation of the posterior body region in the group.<ref name=Hernandez2013/>

== References == {{reflist}}

{{Artiopoda}} {{Taxonbar|from=Q124477198}}

Category:Artiopoda Category:Cambrian first appearances Category:Pennsylvanian extinctions Category:Fossil taxa described in 2013