The tuatara is a reptile endemic to New Zealand which, though it resembles most lizards, is actually part of a distinct lineage, order Sphenodontia.
The tuatara is considered the most unspecialised living amniote; the brain and mode of locomotion resemble that of amphibians and the heart is more primitive than that of any other reptile. Their lungs have a single chamber and lack bronchi.
The tuatara has a third eye on the top of its head called the parietal eye. It has its own lens, cornea, retina with rod-like structures, and degenerated nerve connection to the brain, suggesting it evolved from a real eye. The parietal eye is only visible in hatchlings, which have a translucent patch at the top centre of the skull. After four to six months it becomes covered with opaque scales and pigment.
Together with turtles, the tuatara has the most primitive hearing organs among the amniotes. There is no eardrum and no earhole
Tuatara reproduce very slowly, taking ten to twenty years to reach sexual maturity. It takes the females between one and three years to provide eggs with yolk, and up to seven months to form the shell. It then takes between 12 and 15 months from copulation to hatching. This means reproduction occurs at two- to five-year intervals, the slowest in any reptile. Wild tuatara are known to be still reproducing at about 60 years of age—”Henry”, a 111-year-old tuatara at Southland Museum in Invercargill, New Zealand, became a father (possibly for the first time) on 23 January 2009.