Vicissicaudata

Vicissicaudata Temporal range: Early Cambrian - Late Carboniferous PreꞒ Ꞓ O S D C P T J K Pg N
Sidneyia minor, a vicissicaudatan unplaced in any subgroup
Cheloniellon, a cheloniellid
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
(unranked):	†Artiopoda
(unranked):	†Vicissicaudata Ortega-Hernández, Legg & Braddy, 2013
Subgroupings
†Sidneyia †Emeraldella †Etainia †Kodymirus †Eozetetes †Tardisia[1] †Carimersa †Cheloniellida †Aglaspidida

Vicissicaudata is an unranked group of artiopods, containing Cheloniellida, 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,[2] often ending in a telson and caudal appendages. The morphology of this posterior region varies between clades. Aglaspidids, alongside Eozetetes[3] and Carimersa,[4] 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[5] 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.[6] Most have eyes, although some later aglaspidids and cheloniellids, alongside Tardisia and Etainia,[7] 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),[8] 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,[8] Wheeler Shale,[9] Chengjiang biota,[5] Paseky Shale,[6] Emu Bay Shale,[3] Fezouata Formation,[10] Llanfalteg Formation,[7] Coalbrookdale Formation,[4] Hunsrück Slate[11] and Mazon Creek.[1]

Taxonomy

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,[12] 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.[13]

Etymology

Vicissicaudata translates to "changed tail", in reference to the differentiation of the posterior body region in the group.[2]

References

1. McCoy, Victoria E.; Herrera, Fabiany; Wittry, Jack; Mayer, Paul; Lamsdell, James C. (2025). "A possible vicissicaudatan arthropod from the Late Carboniferous Mazon Creek Lagerstätte". Geological Magazine. 162. doi:10.1017/S001675682400044X.
2. Ortega‐Hernández, Javier; Legg, David A.; Braddy, Simon J. (February 2013). "The phylogeny of aglaspidid arthropods and the internal relationships within Artiopoda". Cladistics. 29 (1): 15–45. doi:10.1111/j.1096-0031.2012.00413.x.
3. Edgecombe, Gregory D.; Paterson, John R.; García-Bellido, Diego C. (January 2017). "A new aglaspidid-like euarthropod from the lower Cambrian Emu Bay Shale of South Australia". Geological Magazine. 154 (1): 87–95. doi:10.1017/s0016756815001053.
4. Briggs, Derek E. G.; Siveter, David J.; Siveter, Derek J.; Sutton, Mark D.; Legg, David; Lamsdell, James C. (August 2023). "A vicissicaudatan arthropod from the Silurian Herefordshire Lagerstätte, UK". Royal Society Open Science. 10 (8). doi:10.1098/rsos.230661. PMC 10394423.
5. Du, Kunsheng; Bruton, David L.; Yang, Jie; Zhang, Xiguang (March 2023). "An early Cambrian Sidneyia (Arthropoda) resolves the century-long debate of its head organization". Science China Earth Sciences. 66 (3): 521–527. doi:10.1007/s11430-022-1019-8.
6. Lamsdell, James C.; Stein, Martin; Selden, Paul A. (September 2013). "Kodymirus and the case for convergence of raptorial appendages in Cambrian arthropods". Naturwissenschaften. 100 (9): 811–825. doi:10.1007/s00114-013-1081-y.
7. Legg, David A.; Hearing, Thomas W. (September 2015). "A late surviving xenopod (Arthropoda) from the Ordovican Period, Wales". Geological Magazine. 152 (5): 942–948. doi:10.1017/S001675681400065X.
8. Stein, Martin; Selden, Paul A. (June 2012). "A restudy of the Burgess Shale (Cambrian) arthropod Emeraldella brocki and reassessment of its affinities". Journal of Systematic Palaeontology. 10 (2): 361–383. doi:10.1080/14772019.2011.566634.
9. Stein, Martin; Church, Stephen B.; Robison, Richard A. (29 September 2011). "A new Cambrian arthropod, Emeraldella brutoni, from Utah". Paleontological Contributions (3). doi:10.17161/PC.1808.8086. hdl:1808/8086.
10. Ortega-HernáNdez, Javier; Van Roy, Peter; Lerosey-Aubril, Rudy (May 2016). "A new aglaspidid euarthropod with a six-segmented trunk from the Lower Ordovician Fezouata Konservat-Lagerstätte, Morocco". Geological Magazine. 153 (3): 524–536. doi:10.1017/S0016756815000710.
11. Stürmer, Wilhelm; Bergström, Jan (June 1978). "The arthropod Cheloniellon from the devonian hunsrück shale". Paläontologische Zeitschrift. 52 (1–2): 57–81. doi:10.1007/BF03006730.
12. Lerosey-Aubril, Rudy; Zhu, Xuejian; Ortega-Hernández, Javier (2017-09-11). "The Vicissicaudata revisited – insights from a new aglaspidid arthropod with caudal appendages from the Furongian of China". Scientific Reports. 7 (1). doi:10.1038/s41598-017-11610-5. ISSN 2045-2322. PMC 5593897. PMID 28894246.
13. Lustri, Lorenzo; Antcliffe, Jonathan B.; Gueriau, Pierre; Daley, Allison C. (October 2024). "New specimens of Bunaia woodwardi Clarke, 1919 (Euchelicerata): a new member of Offacolidae providing insight supporting the Arachnomorpha". Royal Society Open Science. 11 (10). doi:10.1098/rsos.240499. ISSN 2054-5703. PMC 11524597. PMID 39479250.