Cynosphenodon
 Cynosphenodon (/ˌsaɪnəˈsfɛnədɒn/ SY-nə-SFEN-ə-don; Dog Sphenodontian) is an extinct genus of the family Sphenodontidae from the Middle Jurassic La Boca Formation of Tamaulipas Mexico. Growth patterns in the teeth of Cynosphenodon suggest its close relationship with the modern tuatara.