The Tuatara of New Zealand A living relic of a vanished age — why New Zealand's most ancient reptile matters to science he tuatara, Sphenodon punctatus, is found nowhere else in the world outside of New Zealand and its offshore islands. At first glance it resembles a large lizard — a heavy-bodied reptile reaching up to 80 centimetres in length, with a prominent crest of spines along the neck and back, greenish-grey skin, and a powerful jaw. In biological terms, however, it is something far more unusual: the sole surviving member of an ancient reptile order, the Rhynchocephalia, which was widespread across Gondwana during the age of the dinosaurs and has been absent from all other parts of the world for approximately 60 million years. The tuatara is, in the phrase commonly used by biologists, a 'living fossil' — though this term, like many popular shorthand descriptions of evolutionary phenomena, is more poetic than precise. The anatomy of the tuatara reveals features shared with ancient reptile lineages that have no parallel in any modern lizard or snake. Its teeth are unique: rather than being set in sockets as in most reptiles, they are extensions of the jawbone itself, which means they cannot be replaced when worn down. A tuatara that lives long enough will eventually grind its teeth down to the jawbone and be forced to eat only soft food. The tuatara also has a well-developed parietal eye on the top of its head — a light-sensitive organ connected directly to the brain that is believed to play a role in regulating circadian rhythms and seasonal behaviour, though its exact functions remain an active area of research. While all reptiles and many other vertebrates have vestigial remnants of a parietal eye, the tuatara's is among the most structurally complete found in any living animal. The tuatara's physiology sets it apart from most reptiles in ways that reflect its evolutionary isolation. It is cold-adapted to a degree unusual for a reptile, preferring temperatures of 16–21°C and remaining active at night at temperatures that would render most reptiles torpid. It can survive light frosts and remains active in conditions that would kill a lizard of comparable size from a warmer climate. This cold-preference limits its distribution to the temperate offshore islands of New Zealand where predatory mammals — particularly rats and mustelids introduced during European settlement — have been eradicated or never established. The introduction of rats and other mammals to New Zealand following both Polynesian and European settlement had catastrophic consequences for tuatara populations. Rats predate tuatara eggs and young, and the tuatara's reproductive biology — females
reproduce only once every four years, and incubation takes twelve to fifteen months, the longest of any reptile — means that populations recover very slowly from predation pressure. By the early twentieth century, tuatara had been eliminated from the main islands of New Zealand and survived only on a small number of offshore islands that had remained rat-free, including Stephens Island in Cook Strait. Conservation efforts for the tuatara have focused on intensive pest eradication, captive breeding, and translocation to establish new populations on predator-free islands and within predator-proof mainland enclosures. The Department of Conservation's tuatara recovery programme has achieved significant success: populations on key islands have grown substantially, and translocations to several North Island sites have created viable new populations in areas from which tuatara had been absent for centuries. The species is no longer classified as threatened by the New Zealand government, though sustained management will be required to maintain this status. The tuatara's genome, sequenced in 2020, proved to be one of the largest of any reptile and revealed evolutionary signatures consistent with its long isolation. Among the most scientifically significant findings was evidence of extensive gene duplication and a high rate of evolutionary change at certain loci — contrary to the popular assumption that the tuatara's ancient lineage has remained biologically stagnant. The tuatara has not simply remained unchanged since the age of the dinosaurs; it has evolved in its own direction over 60 million years of isolation, and its biology continues to yield insights into the deep history of vertebrate life on Earth.