Willwerathia

Willwerathia is a genus of synziphosurine,[1][2] a paraphyletic group of horseshoe crab-like fossil chelicerate arthropods.[2] Willwerathia known only by one species, Willwerathia laticeps, discovered in deposits of the Devonian period from the Rhenish Slate Mountains of Germany.[1][3]

Willwerathia
Temporal range: Lower Devonian
Reconstruction of Willwerathia laticeps
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Subphylum:
Chelicerata
Order:
Xiphosura
Genus:
†Willwerathia
Størmer, 1969
Species
  • Willwerathia laticeps (Størmer, 1936a)

Morphology
Size comparison of Willwerathia (A) and other synziphosurines.

As a synziphosurine, Willwerathia is unusually large and so far the largest known synziphosurine, with largest carapace measured about 90mm in width.[1] Prosoma of Willwerathia covered by a vaulted carapace with pointed genal spines, recurved (M-shaped) ophthalmic ridges and pairs of dorsal nodes.[1] Tergites of the opisthosoma are either incomplete or disarticulated in available fossil materials, making it difficult to reveal the original number of opisthosomal segments.[1] The opisthosoma of Willwerathia most likely compose of 10 segments, each expressed by a tergite that bore a median dorsal spine and a pair of tergopleurae (lateral extensions).[1] The opisthosoma subdivided into a wider, most likely 7-segmented preabdomen and a narrower, 3-segmented postabdomen.[1] tergite of the first opisthosomal segment is reduced in length while the remaining segments possess well-developed tergites with lateral nodes and posteriorly curved tergopleurae. The final segment terminated with a short, teardrop-shaped telson.[1]

Paleoecology

Willwerathia was most likely a bottom-dwelling predator.[1] The marked articulation surfaces on each of the preabdominal segments suggest that Willwerathia capable to enroll itself in a way similar to Legrandella.[1]

Classification

Willwerathia was originally though to be an eurypterid (sea scorpion), with additional fossils described in 1998 reveal its synziphosurine affinities.[1] In the redescription done by Anderson et al. 1998, Willwerathia had been grouped under the synziphosurine family Weinberginidae alongside Weinbergina and Legrandella,[1] a classification which is not supported by phylogenetic analysis.[2] Willwerathia was regarded as part of the monophyletic Xiphosura sensu stricto (true horseshoe crab) by Lamsdell 2013,[2][4] but further phylogenetic analysis repeatedly resolving it within a clade compose of Bunodids, Pseudoniscids and Dekatriatan (chasmataspidids, eurypterids and arachnids).[5][6][7][8]

References
  1. 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.
  2. 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.
  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. Bicknell, Russell D. C.; Pates, Stephen (2020). "Pictorial Atlas of Fossil and Extant Horseshoe Crabs, With Focus on Xiphosurida". Frontiers in Earth Science. 8. doi:10.3389/feart.2020.00098. ISSN 2296-6463. S2CID 220405124.
  5. Selden, Paul A.; Lamsdell, James C.; Qi, Liu. "An unusual euchelicerate linking horseshoe crabs and eurypterids, from the Lower Devonian (Lochkovian) of Yunnan, China". Zoologica Scripta. 44 (6): n/a. ISSN 0300-3256.
  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. doi:10.1007/s00114-015-1312-5. ISSN 0028-1042. PMID 26391849. S2CID 8153035.
  7. Lamsdell, James C. (2016). "Horseshoe crab phylogeny and independent colonizations of fresh water: ecological invasion as a driver for morphological innovation". Palaeontology. 59 (2): 181–194. doi:10.1111/pala.12220. ISSN 1475-4983.
  8. Bicknell, Russell D. C.; Lustri, Lorenzo; Brougham, Tom (2019-12-01). "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. ISSN 1631-0683.
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