Artiopoda

Cephalon of Peratagnostus cf. nobilis, from Shergold (1980).

Belongs within: Euarthropoda.
Contains: Conciliterga, Aglaspidida, Trilobita, Agnostina.

The Agnostida are a distinctive group of fossil arthropods known from the Cambrian and Ordovician. They were mostly blind, and may have been planktic or pseudoplanktic (Prothero 1998). The affinities of Agnostida have been subject to debate. They have most commonly been regarded as derived trilobites, as indicated by the exoskeletal features of the plesiomorphic Eodiscina. However, preserved appendages of Agnostus are quite different from those known from other trilobites, casting doubt on this relationship (Fortey 2001).

ArtiopodaLSE13
    |--Trilobitomorpha [Emeraldellacea, Naraoiida, Naraoiidae, Nektaspidida]AC17
    |    |  i. s.: HongshiyanaspisAC19
    |    |--+--+--‘Burgessia’ Walcott 1912 non McCook 1894AC19, B95 [Burgessiida]
    |    |  |  |    `--B. bella Walcott 1912CB04
    |    |  |  `--+--Phytophilaspis Ivantsov 1999LSE13, CB04
    |    |  |     `--+--‘Naraoia’ spinosaLSE13
    |    |  |        `--+--Misszhouia Chen et al. 1997LSE13, CB04
    |    |  |           |    `--M. longicaudata (Zhang & Hou 1985)CB04
    |    |  |           `--Naraoia Walcott 1912AC19, CB04
    |    |  |                |  i. s.: N. longicaudataFO99
    |    |  |                |--N. compactaLSE13
    |    |  |                |--N. taijiangensisLSE13
    |    |  |                `--+--N. bertiensisLSE13
    |    |  |                   `--N. spiniferLSE13
    |    |  `--+--KwanyinaspisAC19
    |    |     `--ConcilitergaAC19
    |    `--+--AglaspididaAC19
    |       `--+--+--+--TrilobitaAC19
    |          |  |  `--+--Buenaspis Budd 1999LSE13, CB04
    |          |  |     |    `--B. forteyi Budd 1999CB04
    |          |  |     `--+--CampanamutaLSE13
    |          |  |        `--+--PanlongiaLSE13
    |          |  |           |    |--P. spinosaLSE13
    |          |  |           |    `--P. tetranodosaLSE13
    |          |  |           `--+--+--EmucarisLSE13
    |          |  |              |  `--KangacarisLSE13
    |          |  |              |       |--K. shuiLSE13
    |          |  |              |       `--K. zhangiLSE13
    |          |  |              `--+--Liwia Dzik & Lendzion 1988LSE13, CB04 [Liwiidae]
    |          |  |                 |    `--L. plana (Lendzion 1975)CB04
    |          |  |                 `--+--Tariccoia Hammann et al. 1990CB04
    |          |  |                    |    `--T. arrusensis Hammann et al. 1990CB04
    |          |  |                    `--Soomaspis Fortey & Theron 1994CB04
    |          |  |                         `--S. splendida Fortey & Theron 1994CB04
    |          |  `--PetalopleuraLSE13
    |          |       |--AaveqaspisLSE13
    |          |       `--+--Sinoburius lunaris Hou et al. 1991LSE13, CB04
    |          |          `--+--Acanthomeridion Hou, Chen & Lu 1989LSE13, B95
    |          |             |    `--A. serratumC12
    |          |             `--XandarellidaLSE13
    |          |                  |  i. s.: AlmeniaCB04
    |          |                  |--LuohuilinellaLSE13
    |          |                  `--+--Cindarella eucalla Chen et al. 1996LSE13, CB04
    |          |                     `--Xandarella [Xandarellidae]AC19
    |          |                          `--X. spectaculum Hou et al. 1991CB04
    |          `--+--Sidneyia Walcott 1911AC19, CB04 [Limulavida, Sidneyidea, Sidneyiida]
    |             |    `--S. inexpectans Walcott 1911CB04
    |             `--+--+--MolariidaB95
    |                |  |    |--Molaria Walcott 1912LSE13, CB04
    |                |  |    `--Emeraldoides Simonetta 1964B95
    |                |  `--Emeraldella Walcott 1912AC19, CB04 [Emeraldellida]
    |                |       |--E. brocki Walcott 1912CB04
    |                |       `--E. brutoniLSE13
    |                `--Cheloniellida [Cheloniellonida]LSE13
    |                     |--StrabopidaeS93
    |                     |    |--Strabops thacheri Beecher 1901S93
    |                     |    `--Neostrabops Caster & Macke 1952LSE13, H75
    |                     |         `--N. martini Caster & Macke 1952S93
    |                     `--+--PseudoathronLSE13
    |                        `--+--Cheloniellon Broili 1932LSE13, B95
    |                           |    `--C. calmani Broili 1932CB04
    |                           `--+--Triopus [Triopida]LSE13
    |                              `--+--ParadusliaLSE13
    |                                 `--Duslia Jahn 1893LSE13, S60
    |                                      `--*D. insignis Jahn 1893S60
    `--Agnostida [Miomera]AC17
         |  i. s.: Geragnostella tullbergiFO99
         |         Litagnostus meniscusFO99
         |         Strictagnostus Shergold 1975SS84
         |         Kormagnostella Romanenko 1967 [incl. Litagnostoides Schrank 1975]SS84
         |--AgnostinaS80
         `--Eodiscina [Eodiscoidea]P98
              |  i. s.: CalodiscusP79
              |         HebediscusP79
              |         Triangulaspis Lermontova 1940P79, SS84
              |           `--T. vigilansL95
              |         Pagetia significans (Etheridge 1902)F90, F71 [=Microdiscus significansF71]
              |         LadadiscusF90
              |         Sinodiscus changyanensis Zhang in Zhang et al. 1980F90
              |--WeymouthiidaeRC93
              |    |--Serrodiscus bellimarginatusRC93
              |    `--Cobboldites simplex Cobbold 1931RC93
              `--EodiscidaeRC93
                   |--Tsunyidiscus liangshanensis Chang 1988RC93
                   |--Hupeidiscus orientalis (Chang 1988)RC93
                   |--Opsidiscus depolitusRC93
                   `--Dawsonia Hartt in Dawson 1868 non Brown 1811 (ICBN)M14
Inorganic: Sidneyia groenlandica Cleaves in Cleaves & Fox 1935H75

*Type species of generic name indicated

References

[AC17] Aria, C., & J.-B. Caron. 2017. Burgess Shale fossils illustrate the origin of the mandibulate body plan. Nature 545: 89–92.

[AC19] Aria, C., & J.-B. Caron. 2019. A middle Cambrian arthropod with chelicerae and proto-book gills. Nature 573: 586–589.

[B95] Bousfield, E. L. 1995. A contribution to the natural classification of Lower and Middle Cambrian arthropods: food-gathering and feeding mechanisms. Amphipacifica 2: 3–34.

[C12] Chen, J.-Y. 2012. Evolutionary scenario of the early history of the animal kingdom: evidence from Precambrian (Ediacaran) Weng’an and Early Cambrian Maotianshan biotas, China. In: Talent, J. A. (ed.) Earth and Life: Global biodiversity, extinction intervals and biogeographic perturbations through time pp. 239–379. Springer.

[CB04] Cotton, T. J., & S. J. Braddy. 2004. The phylogeny of arachnomorph arthropods and the origin of the Chelicerata. Transactions of the Royal Society of Edinburgh: Earth Sciences 94: 169–193.

[F71] Fletcher, H. O. 1971. Catalogue of type specimens of fossils in the Australian Museum, Sydney. Australian Museum Memoir 13: 1–167.

[F90] Fortey, R. A. 1990. Ontogeny, hypostome attachment and trilobite classification. Palaeontology 33 (3): 529–576.

[FO99] Fortey, R. A. & R. M. Owens. 1999. Feeding habits in trilobites. Palaeontology 42 (3): 429–465.

[H75] Häntzschel, W. 1975. Treatise on Invertebrate Paleontology pt W. Miscellanea. Supplement 1. Trace Fossils and Problematica, 2nd ed. The Geological Society of America: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[L95] Landing, E. 1995. Upper Placentian–Branchian series of mainland Nova Scotia (middle–upper Lower Cambrian): faunas, paleoenvironments, and stratigraphic revision. Journal of Paleontology 69 (3): 475–495.

[LSE13] Legg, D. A., M. D. Sutton & G. D. Edgecombe. 2013. Arthropod fossil data increase congruence of morphological and molecular phylogenies. Nature Communications 4: 2485.

[M14] Maletz, J. 2014. The classification of the Pterobranchia (Cephalodiscida and Graptolithina). Bulletin of Geosciences 89 (3): 477–540.

[P79] Palmer, A. R. 1979. Cambrian. In: Robison, R. A., & C. Teichert (eds) Treatise on Invertebrate Paleontology pt A. Introduction. Fossilisation (Taphonomy), Biogeography and Biostratigraphy pp. A119–A135. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[P98] Prothero, D. R. 1998. Bringing Fossils to Life: An introduction to paleobiology. WCB McGraw-Hill: Boston.

[RC93] Romano, M., W. T. Chang, W. T. Dean, G. D. Edgecombe, R. A. Fortey, D. J. Holloway, P. D. Lane, A. W. Owen, R. M. Owens, A. R. Palmer, A. W. A. Rushton, J. H. Shergold, D. J. Siveter & M. A. Whyte. 1993. Arthropoda (Trilobita). In: Benton, M. J. (ed.) The Fossil Record 2 pp. 279–296. Chapman & Hall: London.

[S93] Selden, P. A. 1993. Arthropoda (Aglaspidida, Pycnogonida and Chelicerata). In: Benton, M. J. (ed.) The Fossil Record 2 pp. 297–320. Chapman & Hall: London.

[S80] Shergold, J. H. 1980. Late Cambrian trilobites from the Chatsworth Limestone, western Queensland. Bureau of Mineral Resources, Geology and Geophysics—Bulletin 186: 1–111.

[SS84] Shergold, J. H., & K. Sdzuy. 1984. Cambrian and early Tremadocian trilobites from Sultan Dağ, central Turkey. Senckenbergiana Lethaea 65 (1–3): 51–135.

[S60] Smith, A. G. 1960. Amphineura. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt I. Mollusca 1: Mollusca—General Features, Scaphopoda, Amphineura, Monoplacophora, Gastropoda—General Features, Archaeogastropoda and some (mainly Paleozoic) Caenogastropoda and Opisthobranchia pp. I41–I76. Geological Society of America, and University of Kansas Press.

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