Synechodontiformes

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.

Synechodontiformes Temporal range: Early Permian-Paleogene 290.1–37.2 Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N
Fossil of Synechodus ungeri from the Late Jurassic of Germany
Fossil teeth of Palidiplospinax occultidens (top) and P. enniskilleni
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Clade:	Neoselachii
Order:	†Synechodontiformes Duffin & Ward, 1993[2]
Families
See text

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,^[3][4] with some suggesting that they are basal to the last common ancestor of modern sharks and rays.^[5] 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.^[6]

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,^[4] the monophyly of the group has been doubted by other authors, who suggest that they represent a paraphyletic group.^[5] 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.^[7]

The oldest known synechodontiform remains are teeth of Synechodus antiquus from the early Permian (Cisuralian) of the Ural Mountains.^[8] However, other authors have considered the attribution to the teeth to Synechodus to be questionable.^[6]

Taxonomy

• †Palaeospinacidae (Regan, 1906).
  • †Antrigoulia (Guinot, Cappetta, & Adnet, 2014). Southern France, Early Cretaceous (Valanginian).^[9]
  • †Palidiplospinax (Klug & Kriwet, 2008). Europe, Early Jurassic
  • †Palaeospinax (Egerton, 1872)^[10] (nomen dubium^[11])
  • †Synechodus (Woodward, 1888) Worldwide, Permian to Eocene^[12]
  • †Nemacanthus (Agassiz, 1837) Worldwide, Permian-Late Triassic (not considered to belong to the family by some authors^[11])
• Incertae sedis
  • †Mucrovenator (Cuny et al., 2001), Northwestern Nevada, USA, Middle Triassic (Anisian, 245 Ma).^[13]
  • †Polyfaciodus (Koot & Cuny, 2014). Oman,^[14] China,^[15] Early Triassic
  • †Safrodus (Koot & Cuny, 2014). Oman,^[14] China,^[15] Early Triassic
  • †Rhomphaiodon (Duffin, 1993) Europe, Late Triassic-Early Jurassic^[5]
  • †Parascylloides (Thies et al, 2016) Europe, Late Triassic^[7]
  • †Keichouodus (Li et al, 2021) China, Middle-Late Triassic^[16]
  • †Rhomaleodus Andreev and Cuny, 2012 Middle Triassic, Bulgaria^[17][7]

Disputed members

These members were classified in the Synechodontiformes by Klug (2010), but are classified by some other authors as Hexanchiformes:^[10][18][7]

• †Orthacodontidae de Beaumont, 1960
  • †Occitanodus (Guinot, Cappetta & Adnet, 2014). France, Early Cretaceous (Valanginian).^[9]
  • †Sphenodus (Agassiz, 1843). Early Jurassic to Paleocene.^[19]
• †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^[20]
  • †Pseudonotidanus (Underwood & Ward, 2004) Early-Middle Jurassic^[20]

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. 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. Maisey, J. G. (April 2012). "What is an 'elasmobranch'? The impact of palaeontology in understanding elasmobranch phylogeny and evolution". Journal of Fish Biology. 80 (5): 918–951. Bibcode:2012JFBio..80..918M. doi:10.1111/j.1095-8649.2012.03245.x. ISSN 0022-1112. PMID 22497368.
6. 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.
7. 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. doi:10.1127/pala/303/2014/137. ISSN 0375-0442.
8. 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.
9. 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.
10. "Bibliography Database | Shark-References". shark-references.com. Retrieved 2023-12-02.
11. Klug, Stefanie; Kriwet, Jürgen (May 2008). "A new basal galeomorph shark (Synechodontiformes, Neoselachii) from the Early Jurassic of Europe". Naturwissenschaften. 95 (5): 443–448. Bibcode:2008NW.....95..443K. doi:10.1007/s00114-007-0341-0. ISSN 0028-1042. PMID 18196213. S2CID 8460659.
12. 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.
13. "Mucrovenator".
14. 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.
15. 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. 624: 111635. doi:10.1016/j.palaeo.2023.111635.
16. Li, Jiachun; Sun, Zuoyu; Cuny, Gilles; Ji, Cheng; Jiang, Dayong; Zhou, Min (January 2022). Cavin, Lionel (ed.). "An unusual shark assemblage from the Ladinian–Carnian interval of South China". Papers in Palaeontology. 8 (1). doi:10.1002/spp2.1404. ISSN 2056-2799.
17. 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. Bibcode:2012JVPal..32..255A. doi:10.1080/02724634.2012.644646. S2CID 84162775.
18. 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.
19. 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.
20. Klug, Stefanie; Kriwet, Jürgen (September 2010). "A new Late Jurassic species of the rare synechodontiform shark, Welcommia (Chondrichthyes, Neoselachii)". Paläontologische Zeitschrift. 84 (3): 413–419. Bibcode:2010PalZ...84..413K. doi:10.1007/s12542-010-0058-9. ISSN 0031-0220. S2CID 129213049.

External links

• Data related to Synechodontiformes at Wikispecies
• Media related to Synechodontiformes at Wikimedia Commons