Synechodontiformes Explained

Synechodontiformes is an extinct order of prehistoric shark-like cartilaginous fish, 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 members of the modern shark group Galeomorphii, while others have considered them to represent a stem-group to modern sharks,^{[1] [2]} with some suggesting that they are basal to the last common ancestor of modern sharks and rays.^[3] 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.^[4]

The main shared characters of the group relate to teeth anatomy. The teeth roots have a distinctive pseudopolyaulacorhize vascularisation pattern, with a depression on the tooth root to where the nutritive grooves are confined. While Klug (2010) recovered the group as monophyletic, the monophyly of the group has been doubted by other authors, who suggest that they represent a paraphyletic group. One family is unambiguously placed in the order, Palaeospinacidae. The families Orthacodontidae, Paraorthacodontidae and Pseudonotidanidae, often considered members of the group, have been alternatively considered as members of the modern shark order Hexanchiformes rather than as members of Synechodontiformes.

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

Taxonomy

• †Palaeospinacidae (Regan, 1906).
  • †Antrigoulia (Guinot, Cappetta, & Adnet, 2014). Southern France, Early Cretaceous (Valanginian).^[6]
  • †Palidiplospinax (Klug & Kriwet, 2008). Europe, Early Jurassic
  • †Palaeospinax (Egerton, 1872)^[7] (nomen dubium^[8])
  • †Synechodus (Woodward, 1888) Worldwide, Permian to Eocene^[9]
  • †Nemacanthus (Agassiz, 1837) Worldwide, Permian-Late Triassic (not considered to belong to the family by some authors)
• Incertae sedis
  • †Mucrovenator (Cuny et al., 2001), Northwestern Nevada, USA, Middle Triassic (Anisian, 245 Ma).^[10]
  • †Polyfaciodus (Koot & Cuny, 2014). Oman,^[11] China,^[12] Early Triassic
  • †Safrodus (Koot & Cuny, 2014). Oman, China, Early Triassic
  • †Rhomphaiodon (Duffin, 1993) Europe, Late Triassic-Early Jurassic
  • †Parascylloides (Thies et al, 2016) Europe, Late Triassic^[13]
  • †Keichouodus (Li et al, 2021) China, Middle-Late Triassic^[14]
  • †Rhomaleodus Andreev and Cuny, 2012 Middle Triassic, Bulgaria^[15]

Disputed members

These members were classified in the Synechodontiformes by Klug (2010), but are classified by some other authors as Hexanchiformes:^[16]

• †Orthacodontidae de Beaumont, 1960
  • †Occitanodus (Guinot, Cappetta & Adnet, 2014). France, Early Cretaceous (Valanginian).
  • †Sphenodus (Agassiz, 1843). Early Jurassic to Paleocene.^[17]
• †Paraorthacodontidae (Klug, 2010)
  • †Macrourogaleus (Fowler, 1947). Southeastern Germany, Late Jurassic (Tithonian, 152-145 Ma).
  • †Paraorthacodus (Glikman, 1957) Worldwide, Early Jurassic-Eocene
• †Pseudonotidanidae Underwood and Ward 2004
  • †Welcommia Cappetta 1990 Early Jurassic-Early Cretaceous, Europe^[18]
  • †Pseudonotidanus (Underwood & Ward, 2004) Early-Middle Jurassic

Notes and References

1. Bazzi . Mohamad . Campione . Nicolás E. . Ahlberg . Per E. . Blom . Henning . Kear . Benjamin P. . 2021-08-10 . Quental . Tiago Bosisio . Tooth morphology elucidates shark evolution across the end-Cretaceous mass extinction . PLOS Biology . en . 19 . 8 . e3001108 . 10.1371/journal.pbio.3001108 . 1545-7885 . 8354442 . 34375335 . free .
2. Klug . Stefanie . 2010 . Monophyly, phylogeny and systematic position of the †Synechodontiformes (Chondrichthyes, Neoselachii) . Zoologica Scripta . en . 39 . 1 . 37–49 . 10.1111/j.1463-6409.2009.00399.x . 1463-6409 . 85265779.
3. Maisey . J. G. . April 2012 . What is an 'elasmobranch'? The impact of palaeontology in understanding elasmobranch phylogeny and evolution . Journal of Fish Biology . en . 80 . 5 . 918–951 . 10.1111/j.1095-8649.2012.03245.x . 22497368 . 2012JFBio..80..918M . 0022-1112.
4. 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 . en . 1–8 . 10.1080/00288306.2023.2214369 . 258840273 . 0028-8306.
5. Ivanov. Alexander. 2005-08-30. Early Permian chondrichthyans of the Middle and South Urals. Revista Brasileira de Paleontologia. 8. 2. 127–138. 10.4072/rbp.2005.2.05.
6. Guinot. Guillaume. Cappetta. Henri. Adnet. Sylvain. March 2014. A rare elasmobranch assemblage from the Valanginian (Lower Cretaceous) of southern France. Cretaceous Research. en. 48. 54–84. 10.1016/j.cretres.2013.11.014. 2014CrRes..48...54G .
7. Web site: Bibliography Database Shark-References . 2023-12-02 . shark-references.com.
8. Klug . Stefanie . Kriwet . Jürgen . May 2008 . A new basal galeomorph shark (Synechodontiformes, Neoselachii) from the Early Jurassic of Europe . Naturwissenschaften . en . 95 . 5 . 443–448 . 10.1007/s00114-007-0341-0 . 18196213 . 2008NW.....95..443K . 8460659 . 0028-1042.
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. en. 131. 3–4. 353–359. 10.1016/j.pgeola.2019.06.004. 2020PrGA..131..353B . 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 . en . 13 . 10 . 891–917 . 2015JSPal..13..891K . 10.1080/14772019.2014.963179 . 1477-2019 . 129741739.
12. Li . Jiachun . Sun . Zuoyu . Cuny . Gilles . Jiang . Dayong . August 2023 . Early Triassic chondrichthyans from the Zuodeng Section, Guangxi Province, South China: Palaeobiological and palaeobiogeographical implications . Palaeogeography, Palaeoclimatology, Palaeoecology . en . 624 . 111635 . 10.1016/j.palaeo.2023.111635.
13. Thies . Detlef . Vespermann . Jürgen . Solcher . Jutta . 2014-12-23 . Two new neoselachian sharks (Elasmobranchii, Neoselachii, Synechodontiformes) from the Rhaetian (Late Triassic) of Europe . Palaeontographica Abteilung A . 303 . 4-6 . 137–167 . 10.1127/pala/303/2014/137 . 0375-0442.
14. Li . Jiachun . Sun . Zuoyu . Cuny . Gilles . Ji . Cheng . Jiang . Dayong . Zhou . Min . January 2022 . Cavin . Lionel . An unusual shark assemblage from the Ladinian–Carnian interval of South China . Papers in Palaeontology . en . 8 . 1 . 10.1002/spp2.1404 . 2056-2799.
15. Plamen S. Andreev & Gilles Cuny . 2012 . New Triassic stem selachimorphs (Chondrichthyes, Elasmobranchii) and their bearing on the evolution of dental enameloid in Neoselachii . Journal of Vertebrate Paleontology . 32 . 2 . 255–266 . 2012JVPal..32..255A . 10.1080/02724634.2012.644646 . 84162775.
16. Klug . Stefanie . January 2010 . Monophyly, phylogeny and systematic position of the †Synechodontiformes (Chondrichthyes, Neoselachii) . Zoologica Scripta . en . 39 . 1 . 37–49 . 10.1111/j.1463-6409.2009.00399.x . 85265779 . 0300-3256.
17. 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 . 10.2517/2016PR009 . 1342-8144 . 133054888.
18. Klug . Stefanie . Kriwet . Jürgen . September 2010 . A new Late Jurassic species of the rare synechodontiform shark, Welcommia (Chondrichthyes, Neoselachii) . Paläontologische Zeitschrift . en . 84 . 3 . 413–419 . 10.1007/s12542-010-0058-9 . 2010PalZ...84..413K . 129213049 . 0031-0220.