| Rhychocephalians Temporal range: Middle Triassic-Holocene ~240–0Ma | |
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| The tuatara is the only surviving member of this once diverse group. | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Sauropsida |
| Superorder: | Lepidosauria |
| Order: | Rhynchocephalia |
Rhynchocephalia is an order of lepidosaurian reptiles that was once formerly diverse but has only one extant species, the tuatara. Rhynchocephalians first appeared in the Middle Triassic 240 million years ago. Contrary to popular belief, tuataras are not living fossils as various extinct rhynchocephalians showed variation in appearance and niche. Examples of this group include Sphenodon, Diphydontosaurus, Clevosaurus, Vadasaurus, and Priosphenodon. Formerly cosmipolitan, they can only be found in New Zealand.
- †Gephyrosauridae
- Sphenodontia Williston 1925
- †Micromenodon
- †Pelecymala
- †Rebbanasaurus
- †Sphenocondor
- Acrosphenodontia Chambi-Trowell et al., 2021
- †Godavarisaurus
- †Planocephalosaurus
- Eusphenodontia Herrera-Flores et al. 2018
- †Brachyrhinodon
- †Clevosaurus
- †Colobops?
- †Lanceirosphenodon
- †Polysphenodon
- Neosphenodontia Herrera-Flores et al. 2018
- †Homoeosaurus
- †Lamarquesaurus
- †Pamizinsaurus
- †Sigmala
- †Tingitana
- †Vadasaurus
- †Whitakersaurus
- †Opisthodontia
- †Pleurosauridae
- †"Sapheosaurs"
- Sphenodontidae
- †Eilenodontinae?
- Sphenodontinae
- †Leptorhynchia DeMar, Jones & Carrano, 2022
- †Leptosaurus
- †Kallimodon
- †Homoeosaurus
- †Vadasaurus
- †Sapheosauridae
- †Pleurosauridae