Synechodontiformes
Temporal range: Early Permian-Paleogene
Fossil teeth of Palidiplospinax occultidens (top) and P. enniskilleni
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Clade: Neoselachii
Order: †Synechodontiformes
Duffin & Ward, 1993[2]
Families

See text

Synechodontiformes is an extinct order of prehistoric shark-like neoselachians, known from the Permian to the Paleogene. They are considered to be members of Neoselachii, the group that contains modern sharks and rays.

Their placement in the group is uncertain, some authors have considered them to be galeomorph crown-group sharks, while others have considered them to represent a stem-group to modern sharks.[3][4] There is also disagreement about the relationships between Triassic and earlier members of the group, only known from isolated teeth, and those from the Jurassic onwards, with the similarity between the two groups possibly being superficial.[5]

They have sometimes been considered a paraphyletic grouping, but Klug (2010) recovered the group as monophyletic.[4] However, other authors continue to treat the families Orthacodontidae and Paraorthacodontidae as members of the Hexanchiformes.[6] Members of the clade are united by two synapomorphies, "pseudopolyaulacorhize tooth root pattern present; labial root depression in basal view present".[4]

The oldest known synechodontiform remains are teeth of Synechodus antiquus from the early Permian (Cisuralian) of the Ural Mountains.[7] However, other authors have considered the attribution to the teeth to Synechodus to be questionable.[5]

Taxonomy

Based on the Shark-References database:[6]

  • †Palaeospinacidae (Regan, 1906).
  • Incertae sedis
    • †Mucrovenator (Cuny et al., 2001), Northwestern Nevada, USA, Middle Triassic (Anisian, 245 Ma).[10]
    • †Polyfaciodus (Koot & Cuny, 2014). Oman, Early Triassic (Olenekian, 251-247 Ma).
    • †Safrodus (Koot & Cuny, 2014). Oman, Early Triassic (Olenekian, 251-247 Ma).[11] Early Triassic, Oman

Disputed members

Both families here were classified in the Synechodontiformes by Klug (2010), but are classified by the Shark-References database as Hexanchiformes:[6][12]

  • †Orthacodontidae de Beaumont, 1960
    • †Occitanodus (Guinot, Cappetta & Adnet, 2014). France, Early Cretaceous (Valanginian).[8]
    • †Sphenodus (Agassiz, 1843). Early Jurassic to Paleocene.[13]
  • †Paraorthacodontidae (Klug, 2010)
  • Incertae sedis
    • †Rhomphaiodon (Duffin, 1993a). Britain, France, Belgium, Luxembourg, and Germany, Late Triassic to Early Jurassic (Norian to Toarcian, 215-175 Ma).

References

  1. ↑ "†order Synechodontiformes Duffin and Ward 1993 (elasmobranch)". Fossilworks.
  2. ↑ C. J. Duffin and D. J. Ward. 1993. The Early Jurassic Palaeospinacid sharks of Lyme Regis, southern England. Belgian Geological Survey, Professional Papers, Elasmobranches et Stratigraphie 264:53-102
  3. ↑ Bazzi, Mohamad; Campione, Nicolás E.; Ahlberg, Per E.; Blom, Henning; Kear, Benjamin P. (2021-08-10). Quental, Tiago Bosisio (ed.). "Tooth morphology elucidates shark evolution across the end-Cretaceous mass extinction". PLOS Biology. 19 (8): e3001108. doi:10.1371/journal.pbio.3001108. ISSN 1545-7885. PMC 8354442. PMID 34375335.
  4. 1 2 3 Klug, Stefanie (2010). "Monophyly, phylogeny and systematic position of the †Synechodontiformes (Chondrichthyes, Neoselachii)". Zoologica Scripta. 39 (1): 37–49. doi:10.1111/j.1463-6409.2009.00399.x. ISSN 1463-6409. S2CID 85265779.
  5. 1 2 Rees, Jan; Campbell, Hamish J.; Simes, John E. (2023-05-21). "The first Triassic elasmobranch teeth from the Southern Hemisphere (Canterbury, New Zealand)". New Zealand Journal of Geology and Geophysics: 1–8. doi:10.1080/00288306.2023.2214369. ISSN 0028-8306. S2CID 258840273.
  6. 1 2 3 4 "Bibliography Database | Shark-References". shark-references.com. Retrieved 2023-12-02.
  7. ↑ Ivanov, Alexander (2005-08-30). "Early Permian chondrichthyans of the Middle and South Urals" (PDF). Revista Brasileira de Paleontologia. 8 (2): 127–138. doi:10.4072/rbp.2005.2.05.
  8. 1 2 Guinot, Guillaume; Cappetta, Henri; Adnet, Sylvain (March 2014). "A rare elasmobranch assemblage from the Valanginian (Lower Cretaceous) of southern France". Cretaceous Research. 48: 54–84. Bibcode:2014CrRes..48...54G. doi:10.1016/j.cretres.2013.11.014.
  9. ↑ Batchelor, Trevor J.; Duffin, Christopher J. (August 2020). "First description of sharks' teeth from the Ferruginous Sands Formation (Aptian, Early Cretaceous) of the Isle of Wight". Proceedings of the Geologists' Association. 131 (3–4): 353–359. Bibcode:2020PrGA..131..353B. doi:10.1016/j.pgeola.2019.06.004. S2CID 199107658.
  10. ↑ https://www.mindat.org/taxon-P162123.html
  11. ↑ Koot, Martha B.; Cuny, Gilles; Orchard, Michael J.; Richoz, Sylvain; Hart, Malcolm B.; Twitchett, Richard J. (2015-10-03). "New hybodontiform and neoselachian sharks from the Lower Triassic of Oman". Journal of Systematic Palaeontology. 13 (10): 891–917. Bibcode:2015JSPal..13..891K. doi:10.1080/14772019.2014.963179. ISSN 1477-2019. S2CID 129741739.
  12. ↑ Klug, Stefanie (January 2010). "Monophyly, phylogeny and systematic position of the †Synechodontiformes (Chondrichthyes, Neoselachii)". Zoologica Scripta. 39 (1): 37–49. doi:10.1111/j.1463-6409.2009.00399.x. ISSN 0300-3256. S2CID 85265779.
  13. ↑ Kanno, Shiori; Nakajima, Yasuhisa; Hikida, Yoshinori; Sato, Tamaki (2017-04-01). "Sphenodus (Chondrichthyes, Neoselachii) from the Upper Cretaceous in Nakagawa Town, Hokkaido, Japan". Paleontological Research. 21 (2): 122. doi:10.2517/2016PR009. ISSN 1342-8144. S2CID 133054888.


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