Cynosphenodon

Cynosphenodon Temporal range: Middle Jurassic PreꞒ Ꞓ O S D C P T J K Pg N
Diagram of preserved skull elements
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Rhynchocephalia
Family:	Sphenodontidae
Genus:	Cynosphenodon Reynoso, 1996
Type species
†Cynosphenodon huizachalensis Reynoso, 1996

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	†Diphydontosaurus Eusphenodontia †Planocephalosaurus †Clevosaurus Neosphenodontia †Homoeosaurus †Pleurosauridae †Leptosaurus +†Kallimodon †Sapheosauridae Sphenodontidae †Eilenodontinae Sphenodontinae †Navajosphenodon †Cynosphenodon †Sphenofontis †Kawasphenodon Sphenodon (tuatara)

References

1. 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.
2. 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
3. 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.