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Tristychius
| Tristychius Temporal range: Early Carboniferous,
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| Restoration of Tristychius | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Family: | †Tristychiidae |
| Genus: | †Tristychius Agassiz, 1837[1] |
| Type species | |
| †Tristychius arcuatus Agassiz, 1837
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Tristychius (from Greek: τρεις treis, 'three' and Greek: στῐ́χος stíkhos 'row')[2] is an extinct genus of euselachian chondrichthyan from the Carboniferous period (Visean). Fossils of T. arcuatus, the type and only species, including fin spines have been found in Scotland.
Tristychius was a small animal, up to about 60 centimetres (2 ft) long. It had a heterocercal caudal fin, and large spines on two dorsal fins.[3] Unlike other chondrichthyans that have three basal plates on pectoral fin (propterygium, mesopterygium and metapterygium), its pectoral fin had only two basal plates and lacked mesopterygium.[4] Even through it is one of the earliest known stem-elasmobranchs, it is estimated to be a specialized suction feeding benthic predator, either ambushing or using stealth to approach its prey.[5] While historically considered a hybodont, a 2016 study considered it to be a basal euselachian, with hybodonts more closely related to Neoselachii (the group of modern sharks and rays) than to Tristychius. The study placed the genus in the family Tristychiidae along with Acronemus.[6]
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Holocephali (chimaeras and relatives) | |||||||||||||||||||
| Euselachii |
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- ^ L. Agassiz. 1837. Recherches Sur Les Poissons Fossiles. Tome III (livr. 8-9). Imprimérie de Petitpierre, Neuchatel viii-72
- ^ Roberts, George (1839). An etymological and explanatory dictionary of the terms and language of geology. London: Longman, Orme, Brown, Green, & Longmans. p. 174. Retrieved 1 January 2022.
- ^ Dick, John R. F. (1978). "On the Carboniferous shark Tristychius arcuatus Agassiz from Scotland". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 70 (4): 63–108. doi:10.1017/S0080456800012898. ISSN 2053-5945. S2CID 130713238.
- ^ Coates, Michael I.; Gess, Robert W. (2007). "A New Reconstruction of Onychoselache traqairi, Comments on Early Chondrichthyan Pectoral Gridles and Hybodontiform Phylogeny". Palaeontology. 50 (6): 1421–1446. Bibcode:2007Palgy..50.1421C. doi:10.1111/j.1475-4983.2007.00719.x. ISSN 0031-0239. S2CID 140556654.
- ^ Coates, Michael I.; Tietjen, Kristen; Olsen, Aaron M.; Finarelli, John A. (2019-09-06). "High-performance suction feeding in an early elasmobranch". Science Advances. 5 (9): eaax2742. Bibcode:2019SciA....5.2742C. doi:10.1126/sciadv.aax2742. ISSN 2375-2548. PMC 6739094. PMID 31535026.
- ^ Coates, Michael I.; Tietjen, Kristen (March 2017). "The neurocranium of the Lower Carboniferous shark Tristychius arcuatus (Agassiz, )". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 108 (1): 19–35. Bibcode:2017EESTR.108...19C. doi:10.1017/S1755691018000130. ISSN 1755-6910. S2CID 135297534.
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