Synechodontiformes Temporal range:Early Permian-Paleogene290.1–37.2 Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N
Fossil ofSynechodus ungeri from the Late Jurassic of Germany
Fossil teeth ofPalidiplospinax occultidens (top) andP. enniskilleni
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Order:	†Synechodontiformes Duffin & Ward, 1993[2]
Families
See text

Synechodontiformes is an extinctorder of prehistoricshark-likecartilaginous fish, known from thePermian to thePaleogene. They are considered to be members ofNeoselachii, 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 groupGaleomorphi, while others have considered them to represent astem-group to modern sharks,^[3][4] with some suggesting that they arebasal to the last common ancestor of modern sharks and rays.^[5] There is also disagreement about the relationships betweenTriassic and earlier members of the group, only known from isolated teeth, and those from theJurassic 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 pseudopolyaulacorhizevascularisation pattern, with a depression on the tooth root to where the nutritive grooves are confined.^[4] While Klug (2010) recovered the group asmonophyletic,^[4] the monophyly of the group has been doubted by other authors, who suggest that they represent aparaphyletic group,^[5] and that the tooth vascularisation patterns do not clearly demonstrate that these sharks are more closely related to each other than to other sharks.^[7] One family is unambiguously placed in the order,Palaeospinacidae. The familiesOrthacodontidae,Paraorthacodontidae andPseudonotidanidae, often considered members of the group, have been alternatively considered as members of the modern shark orderHexanchiformes rather than as members of Synechodontiformes.^[7][8]

The oldest known synechodontiform remains are teeth ofSynechodus antiquus from the early Permian (Cisuralian) of the Ural Mountains.^[9] However, other authors have considered the attribution to the teeth toSynechodus to be questionable.^[6]

• †Palaeospinacidae (Regan, 1906).
  • †Antrigoulia (Guinot, Cappetta, & Adnet, 2014). Southern France, Early Cretaceous (Valanginian).^[10]
  • †Palidiplospinax (Klug & Kriwet, 2008). Europe, Early Jurassic
  • †Palaeospinax (Egerton, 1872)^[11] (nomen dubium^[12])
  • †Synechodus (Woodward, 1888) Worldwide, Permian toEocene^[13]
  • †Nemacanthus (Agassiz, 1837) Worldwide, Permian-Late Triassic (not considered to belong to the family by some authors^[12])
• Incertae sedis
  • †Mucrovenator (Cuny et al., 2001), Northwestern Nevada, USA, Middle Triassic (Anisian, 245 Ma).^[14]
  • †Polyfaciodus (Koot & Cuny, 2014). Oman,^[15] China,^[16] Early Triassic
  • †Safrodus (Koot & Cuny, 2014). Oman,^[15] China,^[16] Early Triassic
  • †Rhomphaiodon (Duffin, 1993) Europe, Late Triassic-Early Jurassic^[5]
  • †Parascylloides (Thies et al, 2016) Europe, Late Triassic^[8]
  • †Keichouodus (Li et al, 2021) China, Middle-Late Triassic^[17]
  • †Rhomaleodus Andreev and Cuny, 2012 Middle Triassic, Bulgaria^[18][8]

These members were classified in the Synechodontiformes by Klug (2010), but are classified by some other authors as Hexanchiformes:^{[11][19][8][7]}

• †Orthacodontidae de Beaumont, 1960
  • †Occitanodus (Guinot, Cappetta & Adnet, 2014). France, Early Cretaceous (Valanginian).^[10]
  • †Sphenodus (Agassiz, 1843). Early Jurassic to Paleocene.^[20]
  • Archaeogracilidens (Villalobos-Segura et al. 2025), Germany, Late Jurassic^[7]
• †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^[21]
  • †Pseudonotidanus (Underwood & Ward, 2004) Early-Middle Jurassic^[21]

• Data related toSynechodontiformes at Wikispecies
• Media related toSynechodontiformes at Wikimedia Commons

• Synechodontiformes
• Prehistoric cartilaginous fish orders
• Permian first appearances
• Lopingian taxonomic orders
• Early Triassic taxonomic orders
• Middle Triassic taxonomic orders
• Late Triassic taxonomic orders
• Early Jurassic taxonomic orders
• Middle Jurassic taxonomic orders
• Late Jurassic taxonomic orders
• Early Cretaceous taxonomic orders
• Late Cretaceous taxonomic orders
• Paleocene taxonomic orders
• Paleogene extinctions

• Articles with short description
• Short description is different from Wikidata
• Articles with 'species' microformats
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