| Cynosphenodon Temporal range:
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| Diagram of preserved skull elements | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Rhynchocephalia |
| Family: | Sphenodontidae |
| Genus: | Cynosphenodon Reynoso, 1996 |
| Type species | |
| †Cynosphenodon huizachalensis Reynoso, 1996
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Cynosphenodon (/ˌsaɪnəˈsfɛnədɒn/ SY-nə-SFEN-ə-don; "Dog Sphenodontian") is an extinct genus of rhynchocephalian in the family Sphenodontidae from the Middle Jurassic La Boca Formation of Tamaulipas, Mexico. It is known from a largely complete lower jaw and fragments of the upper jaw. It is suggested to be among the closest known relatives of the tuatara, with both being placed in the Sphenodontinae,[1] which is supported by among other characters, the growth pattern of the teeth.[2]
Cladogram after Simoes et al. 2022.[3]
| Sphenodontia |
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- ^ Reynoso, Victor-Hugo (1996). "A Middle Jurassic Sphenodon-like sphenodontian (Diapsida: Lepidosauria) from Huizachal Canyon, Tamaulipas, Mexico". Journal of Vertebrate Paleontology. 16 (2): 210–221. Bibcode:1996JVPal..16..210R. doi:10.1080/02724634.1996.10011309. ISSN 0272-4634.
- ^ Reynoso, V. H. (2003). Growth patterns and ontogenetic variation of the teeth and jaws of the Middle Jurassic sphenodontian Cynosphenodon huizachalensis (Reptilia: Rhynchocephalia). Canadian Journal of Earth Sciences 40(4), 609–619
- ^ Simões, Tiago R.; Kinney-Broderick, Grace; Pierce, Stephanie E. (2022-03-03). "An exceptionally preserved Sphenodon-like sphenodontian reveals deep time conservation of the tuatara skeleton and ontogeny". Communications Biology. 5 (1): 195. doi:10.1038/s42003-022-03144-y. ISSN 2399-3642. PMC 8894340. PMID 35241764.