Tuatara
There are two extant subspecies: Sphenodon punctatus and the much rarer Sphenodon guntheri, or Brothers Island tuatara which is confined to Brothers Island in Cook Strait; it has olive skin with yellowish patches.
Though it resembles a lizard, it has several characteristics unique among reptiles. Its teeth are fused to its jaw bone; it has no external copulatory organs or earholes. Indeed, tuatara were originally classified as lizards in 1831 when the British Museum received a skull. The species remained misclassified until 1867, when Gunther (also at the British Museum) noted certain bird-like, turtle-like, and crocodile-like features and proposed the order Rhynchocephalia for the tuatara and its fossile relatives.
The name tuatara derives from the Māori language, meaning "spiny back". Tuatara feature in a number of indiginous legends; they are ariki (God forms). Tuatara are regarded as the messenger of Whiro, the god of death and disaster. Māori women are forbidden to eat tuatara.
It thrives in much lower temperatures than are tolerated by most reptiles, preferring temperatures of 60 to 70 degrees Fahrenheit (16-21 C); temperatures over 80 (27) degrees are fatal. Adults are about 50cm long and weigh maybe three kilograms. Tuatara are notoriously cryptic, and hibernate in winter. Adults are terrestrial and nocturnal, but hatchlings are arboreal and diurnal (likely because the adults are known to eat younger tuatara).
It is extremely long-lived, with individuals commonly living for over a century, and reproduces very slowly: tuataras take at least ten years to reach sexual maturity, females only lay eggs once every four years, and it takes between 12 and 15 months after copulation for a new tuatara to hatch from its egg. The sex of the hatchling depends on the temperature of the egg; warmer eggs tend to produce male tuatara.
Like some lizards, the tuatara has a third eye on the top of its head; in adult animals a scale grows over the eye, and its purpose isn't clear.