Temporal range: Upper Triassic – Recent
Sphenodontia is an order of lizard-like reptiles that includes only one living genus, the tuatara (Sphenodon).
The sphenodonts (or rhynchocephalids) are an offshoot from the evolutionary line leading to the true lizards and snakes. They had many families during the late Triassic and Jurassic periods but then declined, and are the least successful of the lepidosaurs.
The only surviving member today is the New Zealand tuatara.