Synziphosurina

Synziphosurina is a paraphyletic group of chelicerate arthropods previously thought to be basal horseshoe crabs (Xiphosura).[4] It was later identified as a grade composed of various basal euchelicerates,[4][5][6][3][2] eventually excluded form the monophyletic Xiphosura sensu stricto[4] and only regarded as horseshoe crabs under a broader sense ('Xiphosura' sensu lato).[3][5] Synziphosurines survived at least since early Ordovician to early Carboniferous in ages, with most species are known from the in-between Silurian strata.[2]

Fossil of Weinbergina opitzi with preserved ventral appendages.
  • Dorsal morphology and variation of opisthosomal segmentation across synziphosurines.
    Dorsal morphology and variation of opisthosomal segmentation across synziphosurines.
Size comparison of various synziphosurines.

Synziphosurina
Temporal range:
Venustulus waukeshaensis (top left), Cyamocephalus loganensis (top right), Weinbergina opitzi (center), Limuloides limuloides (bottom left), and Legrandella lombardii (bottom right).
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Clade: Prosomapoda
Suborder: †Synziphosurina
Packard 1886
Genera[1][2][3]

While Weinbergina and Willwerathia being exceptionally large,[7] most synziphosurines are small arthropods with body length ranging only about a few centimeters long.[8]

The body of synziphosurine composed of a prosoma covered by a dome-like carapace (prosomal dorsal shield) and an opisthosoma with usually unfused 9-11 segments expressed by tergites.[2] With the exception of Pseudoniscus[8] and Pasternakevia,[9] the last 3 opisthosomal segments precede the spine-like telson are specialized into a narrow postabdomen (pretelson),[2] while the remaining wider segments referred to as preabdomen.[8] A reduced anteriormost tergite (microtergite) originated from the first opisthosomal segment is observable at least in some genera.[8][4] Most synziphosurines are possibly blind, with only a few species showing possible (e.g. Weinbergina opitzi) or clear (e.g. Legrandella lombardii) evidences of lateral compound eyes on their carapaces.[10][2] Evidences of appendages are scarce, fragmentary known from Anderella parva,[11] Camanchia grovensis[12] and Venustulus waukeshaensis[13] while exceptionally well-documented in Weinbergina opitzi.[14][2] The prosoma possess a pair of chelicerae and at least 5 pairs of walking legs while the opisthosoma probably has 6 pairs of plate-like opercula.[4][15]

As of 2020, at least 13 genera and 20 species were considered to be synziphosurines.[2] The even basal euchelicerates Offacolus and Dibasterium, the questionable genus Borchgrevinkium, as well as the Dekatriata-related Houia and Winneshiekia, may also regarded as members of synziphosurines in some literatures.[16][5][6][17][2]

References
  1. W. Krzemiński, E. Krzemińska, and D. Wojciechowski. 2010. Silurian synziphosurine horseshoe crab Pasternakevia revisited. Acta Palaeontologica Polonica 55(1):133-139 [A. Hendy/A. Hendy/J. Karr]
  2. Bicknell, Russell D. C.; Pates, Stephen (2020). "Pictorial Atlas of Fossil and Extant Horseshoe Crabs, With Focus on Xiphosurida". Frontiers in Earth Science. 8: 98. Bibcode:2020FrEaS...8...98B. doi:10.3389/feart.2020.00098. ISSN 2296-6463.
  3. Dunlop, J. A.; Penney, D.; Jekel, D. (2020). "A summary list of fossil spiders and their relatives" (PDF). World Spider Catalog. Natural History Museum Bern. pp. 1–296.
  4. Lamsdell, James C. (2013-01-01). "Revised systematics of Palaeozoic 'horseshoe crabs' and the myth of monophyletic Xiphosura". Zoological Journal of the Linnean Society. 167 (1): 1–27. doi:10.1111/j.1096-3642.2012.00874.x. ISSN 0024-4082.
  5. Selden, Paul A.; Lamsdell, James C.; Qi, Liu (2015). "An unusual euchelicerate linking horseshoe crabs and eurypterids, from the Lower Devonian (Lochkovian) of Yunnan, China". Zoologica Scripta. 44 (6): 645–652. doi:10.1111/zsc.12124. ISSN 0300-3256. S2CID 55264483.
  6. Lamsdell, James C.; Briggs, Derek E. G.; Liu, Huaibao P.; Witzke, Brian J.; McKay, Robert M. (2015). "A new Ordovician arthropod from the Winneshiek Lagerstätte of Iowa (USA) reveals the ground plan of eurypterids and chasmataspidids". The Science of Nature. 102 (9–10): 63. Bibcode:2015SciNa.102...63L. doi:10.1007/s00114-015-1312-5. ISSN 0028-1042. PMID 26391849. S2CID 8153035.
  7. Anderson, Lyall I.; Poschmann, Markus; Brauckmann, Carsten (1998). "On the Emsian (Lower Devonian) arthropods of the Rhenish Slate Mountains: 2. The synziphosurine Willwerathia". Paläontologische Zeitschrift. 72 (3–4): 325–336. doi:10.1007/BF02988363. ISSN 0031-0220. S2CID 128464147.
  8. Eldredge, Niles; Smith, LeGrande (1974). "Revision of the suborder Synziphosurina (Chelicerata, Merostomata) : with remarks on merostome phylogeny. American Museum novitates ; no. 2543". hdl:2246/2745. {{cite journal}}: Cite journal requires |journal= (help)
  9. Krzemiński, Wiesław; Krzemińska, Ewa; Wojciechowski, Dariusz (2010). "Silurian Synziphosurine Horseshoe Crab Pasternakevia Revisited". Acta Palaeontologica Polonica. 55 (1): 133–139. doi:10.4202/app.2008.0074. ISSN 0567-7920.
  10. Bicknell, Russell D. C.; Amati, Lisa; Ortega-Hernández, Javier (2019-11-14). "New insights into the evolution of lateral compound eyes in Palaeozoic horseshoe crabs". Zoological Journal of the Linnean Society. 187 (4): 1061–1077. doi:10.1093/zoolinnean/zlz065. ISSN 0024-4082.
  11. Moore, Rachel A.; McKENZIE, Scott C.; Lieberman, Bruce S. (2007). "A Carboniferous Synziphosurine (xiphosura) from the Bear Gulch Limestone, Montana, Usa". Palaeontology. 50 (4): 1013–1019. doi:10.1111/j.1475-4983.2007.00685.x. ISSN 1475-4983. S2CID 59449700.
  12. MOORE, RACHEL A.; BRIGGS, DEREK E. G.; BRADDY, SIMON J.; SHULTZ, JEFFREY W. (2011). "Synziphosurines (Xiphosura: Chelicerata) from the Silurian of Iowa". Journal of Paleontology. 85 (1): 83–91. doi:10.1666/10-057.1. ISSN 0022-3360. JSTOR 23019501. S2CID 115132351.
  13. Moore, Rachel A.; Briggs, Derek E. G.; Braddy, Simon J.; Anderson, Lyall I.; Mikulic, Donald G.; Kluessendorf, Joanne (2005). "A new synziphosurine (Chelicerata : Xiphosura) from the Late Llandovery (Silurian) Waukesha Lagerstatte, Wisconsin, USA". Journal of Paleontology. 79 (2): 242–250. doi:10.1666/0022-3360(2005)079<0242:ANSCXF>2.0.CO;2. ISSN 0022-3360. S2CID 56570105.
  14. Moore, Rachel A.; Briggs, Derek E. G.; Bartels, Christoph (2005). "A new specimen ofWeinbergina opitzi (Chelicerata: Xiphosura) from the Lower Devonian Hunsriick Slate, Germany". Paläontologische Zeitschrift. 79 (3): 399–408. doi:10.1007/BF02991931. ISSN 0031-0220. S2CID 84994966.
  15. Dunlop, Jason A.; Lamsdell, James C. (2017). "Segmentation and tagmosis in Chelicerata". Arthropod Structure & Development. 46 (3): 395–418. doi:10.1016/j.asd.2016.05.002. ISSN 1467-8039. PMID 27240897.
  16. Briggs, Derek E. G.; Siveter, Derek J.; Siveter, David J.; Sutton, Mark D.; Garwood, Russell J.; Legg, David (2012-09-25). "Silurian horseshoe crab illuminates the evolution of arthropod limbs". Proceedings of the National Academy of Sciences. 109 (39): 15702–15705. Bibcode:2012PNAS..10915702B. doi:10.1073/pnas.1205875109. ISSN 0027-8424. PMC 3465403. PMID 22967511.
  17. Bicknell, Russell D.C.; Lustri, Lorenzo; Brougham, Tom (2019). "Revision of "Bellinurus" carteri (Chelicerata: Xiphosura) from the Late Devonian of Pennsylvania, USA". Comptes Rendus Palevol. 18 (8): 967–976. doi:10.1016/j.crpv.2019.08.002.
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