Sphenodontidae

Sphenodontidae is a family within the reptile group Rhynchocephalia, comprising taxa most closely related to the living tuatara of the genus "Sphenodon". The included taxa within Sphenodontidae have varied greatly between analyses, and the group has lacked a formal definition. "Cynosphenodon" from the Early Jurassic of Mexico has consistently been recovered as a close relative of the tuatara in most analyses.
The following is a cladogram of Rhynchocephalia after Rauhut "et al." (2012):