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Superregnum: Eukaryota
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Cladus: Craniata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Cladus: Reptiliomorpha
Cladus: Amniota
Classis: Reptilia
Cladus: Eureptilia
Cladus: Romeriida
Subclassis: Diapsida
Infraclasses: Sauria
Ordo: †Ichthyosauria
Ordines incertae sedis: †Araeoscelidia – †Coelurosauravidae – †Drepanosauridae – †Longisquamidae – †Younginiformes


Diapsida Osborn, 1903
Alternative classifications
Bakker (1986)

Bakker, Robert T. (1986), The Dinosaur Heresies, William Morrow.

Superclass Diapsida

  • “Lizards”
  • “Snakes”
  • “Turtles”?
    • Class Archosauria
      • “Rhynchosaurs”?
      • “Crimson crocs”
      • “Ornithosuchids”
      • “Phytosaurs”
      • “Aetosaurs”
      • “Crocodilians”
      • Subclass Dinosauria
        • Lagosuchus
        • Order Pterosauria
          • “Dimorphodons”
          • “Rhamphorynchs”
          • Pterodaustro
          • “Pterodactylids”
          • “Ornithocheirs”
        • Infraclass Phytodinosauria
          • “Anchisaurs”
          • Superorder Sauropoda
            • “Cetiosaurs”
            • “Brachiosaurs”
            • “Diplodocids”
            • “Titanosaurs”
          • Superorder Predentata
            • Ornithopoda
              • “Heterodontosaurs”
              • “Nanosaurs”
              • “Hypsilophodonts”
              • “Iguanodonts”
              • “Hadrosaurs”
            • Thyreophora
              • Orbitoscuta
                • “Pachycephalosaurs”
                • “Scelidosaurs”
                • “Stegosaurs”
                • Ankylosauria
                  • “Nodosaurs”
                  • “Ankylosaurids”
              • Ceratopsia
                • “Psittacosaurs”
                • “Protoceratopsids”
                • “Ceratopsids”
        • “Herrerasaurs”
        • Infraclass Theropoda
          • “Podokesaurs”
          • Neotheropoda
            • "Ceratosaurs"
            • Dinoaves
              • “Allosaurs”
              • “Ornithomimids”
              • “Tyrannosaurs”
              • “Dromaeosaurs”
              • Superorder Aves
                • Archaeopteryx
                • Ichthyornis
                • Hesperornis
                • “Modern birds”

Pough et al. (2006)

From The vertebrate life, 6th ed.

[Fig. 16.1:]


  • basal diapsids†
  • Sauria (Neodiapsida)
    • Archosauromorpha
      • Rhynchosauria†
      • Prolacertiformes†
      • Archosauria
        • Proterosuchidae†
        • Erythrosuchidae†
        • Crurotarsi
          • Ornithosuchidae†
          • Phytosauridae†
          • Stagonolepidae†
          • Rauisuchia†
          • Crocodylomorpha
        • Ornithodira
          • Pterosauria†
          • Dinosauria
            • Ornithischia†
            • Saurischia†
              • Aves
    • Lepidosauromorpha
      • Sauropterygia†
        • Placodontia†
        • Plesiosauria†
      • Lepidosauria
        • Sphenodontia
        • Squamata
    • ?Ichthyosauria†

Vernacular names
Deutsch: Diapside Reptilien
English: Diapsid
español: Dyapsida
suomi: Diapsidit
français: Diapsides
日本語: 双弓類
한국어: 이궁류
polski: diapsydy
українська: Діапсиди
中文: 雙孔亞綱

Diapsids ("two arches") are a group of amniote tetrapods that developed two holes (temporal fenestra) in each side of their skulls about 300 million years ago during the late Carboniferous period.[1] The diapsids are extremely diverse, and include all crocodilians, lizards, snakes, tuatara, turtles, and birds.[2] Although some diapsids have lost either one hole (lizards), or both holes (snakes and turtles), or have a heavily restructured skull (modern birds), they are still classified as diapsids based on their ancestry. At least 17,084 species of diapsid animals are extant: 9,159 birds,[3] and 7,925 snakes, lizards, tuatara, turtles, and crocodiles.[4]

Diagram of the diapsid skull with temporal openings, unlike in Anapsida

The name Diapsida means "two arches", and diapsids are traditionally classified based on their two ancestral skull openings (temporal fenestrae) posteriorly above and below the eye. This arrangement allows for the attachment of larger, stronger jaw muscles, and enables the jaw to open more widely. A more obscure ancestral characteristic is a relatively long lower arm bone (the radius) compared to the upper arm bone (humerus).

Diapsids were originally classified as one of four subclasses of the class Reptilia, all of which were based on the number and arrangement of openings in the skull. The other three subclasses were Synapsida (one opening low on the skull, for the "mammal-like reptiles"), Anapsida (no skull opening, including turtles and their relatives), and Euryapsida (one opening high on the skull, including many prehistoric marine reptiles). With the advent of phylogenetic nomenclature, this system of classification was heavily modified. Today, the synapsids are often not considered true reptiles, while Euryapsida were found to be an unnatural assemblage of diapsids that had lost one of their skull openings. Genetic studies and the discovery of the Triassic Pappochelys have shown that this is also the case in turtles, which are actually heavily modified diapsids. In phylogenetic systems, birds (descendants of traditional diapsid reptiles) are also considered to be members of this group.

Some modern studies of reptile relationships have preferred to use the name "diapsid" to refer to the crown group of all modern diapsid reptiles but not their extinct relatives. However, many researchers have also favored a more traditional definition that includes the prehistoric araeoscelidians. In 1991, Laurin defined Diapsida as a clade, "the most recent common ancestor of araeoscelidians, lepidosaurs, and archosaurs, and all its descendants".[5]

A cladistic analysis by Laurin and Piñeiro (2017) recovers Parareptilia as part of Diapsida, with pareiasaurs, turtles, millerettids, and procolophinoids recovered as more derived than the basal diapsid Younginia.[6]

Below is a cladogram showing the relations of the major groups of diapsids.

Cladogram after Bickelmann et al., 2009[7] and Reisz et al., 2011:[8]


Millerettidae Milleretta BW.jpg




Lanthanosuchidae Lanthanosuchus watsoni.jpg


Procolophonoidea Sclerosaurus1DB.jpg

Pareiasauromorpha Scutosaurus BW.jpg


Captorhinidae Labidosaurus.jpg




















See also

Vertebrate paleontology


"Those diverse diapsids".
Schoch, Rainer R.; Sues, Hans-Dieter (2016). "The diapsid origin of turtles". Zoology. 119 (3): 159–161. doi:10.1016/j.zool.2016.01.004. PMID 26934902.
Barrowclough, George F.; Cracraft, Joel; Klicka, John; Zink, Robert M. (23 November 2016). "How Many Kinds of Birds Are There and Why Does It Matter?". PLOS ONE. 11 (11): e0166307. doi:10.1371/journal.pone.0166307. PMC 5120813.
Reeder, Tod W.; Townsend, Ted M.; Mulcahy, Daniel G.; Noonan, Brice P.; Wood, Perry L.; Sites, Jack W.; Wiens, John J. (2015). "Integrated Analyses Resolve Conflicts over Squamate Reptile Phylogeny and Reveal Unexpected Placements for Fossil Taxa". PLOS ONE. 10 (3): e0118199. Bibcode:2015PLoSO..1018199R. doi:10.1371/journal.pone.0118199. PMC 4372529. PMID 25803280.
Benton, M. J., Donoghue, P. C., Asher, R. J., Friedman, M., Near, T. J., & Vinther, J. (2015). "Constraints on the timescale of animal evolutionary history." Palaeontologia Electronica, 18.1.1FC; 1-106;
Laurin, Michel; Piñeiro, Graciela H. (2017). "A Reassessment of the Taxonomic Position of Mesosaurs, and a Surprising Phylogeny of Early Amniotes" (PDF). Frontiers in Earth Science. 5: 88. Bibcode:2017FrEaS...5...88L. doi:10.3389/feart.2017.00088. S2CID 32426159.
Constanze Bickelmann, Johannes Müller and Robert R. Reisz (2009). "The enigmatic diapsid Acerosodontosaurus piveteaui (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of younginiform reptiles". Canadian Journal of Earth Sciences. 49 (9): 651–661. Bibcode:2009CaJES..46..651S. doi:10.1139/E09-038.
Robert R. Reisz, Sean P. Modesto and Diane M. Scott (2011). "A new Early Permian reptile and its significance in early diapsid evolution". Proceedings of the Royal Society B. 278 (1725): 3731–7. doi:10.1098/rspb.2011.0439. PMC 3203498. PMID 21525061.

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