moreha tekor akhe: rib tattoo

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Tuatara are greenish brown, and measure up to 80 cm (31 in) from head to tail-tip and weigh up to 1.3 kilograms (2.9 lb) with a spiny crest along the back, especially pronounced in males. Their dentition, in which two rows of teeth in the upper jaw overlap one row on the lower jaw, is unique among living species. They are further unusual in having a pronounced photo-receptive eye dubbed the "third eye", whose current function is a subject of ongoing research but is thought to be involved in setting circadian and seasonal cycles. They are able to hear although no external ear is present, and have a number of unique features in their skeleton, some of them apparently evolutionarily retained from fish. Although tuatara are sometimes called "living fossils", recent taxonomic and molecular work has shown that they have changed significantly since the Mesozoic era.

The name "tuatara" derives from the Māori language, and means "peaks on the back". As with many other Māori loanwords, the plural form is now generally the same as the singular in formal New Zealand English usage. "Tuataras" remains common in less formal speech, particularly among older speakers. The tuatara has been protected by law since 1895 (the second species, S. guntheri, was not recognised until 1989). Tuatara, like many of New Zealand's native animals, are threatened by habitat loss and introduced predators like the Polynesian Rat (Rattus exulans). They were extinct on the mainland, with the remaining populations confined to 32 offshore islands, until the first mainland release into the heavily fenced and monitored Karori Sanctuary in 2005.

Tuatara were originally classified as lizards in 1831 when the British Museum received a skull. The genus remained misclassified until 1867, when Albert Günther of the British Museum noted features similar to birds, turtles, and crocodiles. He proposed the order Rhynchocephalia (meaning "beak head") for the tuatara and its fossil relatives. Now, most authors prefer to use the more exclusive order name of Sphenodontia for the tuatara and its closest living relatives.

There are two extant species: Sphenodon punctatus and the much rarer Sphenodon guntheri, or Brothers Island tuatara, which is confined to North Brother Island in Cook Strait. The species name punctatus is Latin for "spotted", and guntheri refers to Albert Günther. S. punctatus was named when only one species was known, and its name is misleading, since both species can have spots. The Brother's Island tuatara (S. guntheri) has olive brown skin with yellowish patches, while the colour of the other species, (S. punctatus), ranges from olive green through grey to dark pink or brick red, often mottled, and always with white spots. In addition, S. guntheri is considerably smaller. A third, extinct species of Sphenodon was identified in November 1885 by William Colenso, who was sent an incomplete sub-fossil specimen from a local coal mine. Colenso named the new species S. diversum. Sphenodon punctatus is further divided into two subspecies: the Cook Strait tuatara (unnamed subspecies), which lives on other islands in and near Cook Strait, and the northern tuatara (Sphenodon punctatus punctatus), which lives on the Bay of Plenty, and some islands further north. A 2009 paper reexamined the genetic bases used to distinguish the two species of tuatara, and concluded that they only represent geographic variants, and only one species should be recognized.