Reptiles
Tuatara
Sphenodon punctatus · also called living fossil
The tuatara is often called a living fossil, and for once the phrase is close to fair. It is the last twig of a branch of the reptile family tree that split off before the dinosaurs, and it survives today only in New Zealand, mostly on scattered islands cleared of introduced predators.
Overview
Tuatara live in coastal forest and scrub, typically where seabirds nest in burrows. The two share the ground: the tuatara often takes over a petrel or shearwater burrow to shelter in, eats some of the birds’ eggs and chicks, and benefits from the rich, insect-filled soil the colony creates. Tuatara are nocturnal as adults, emerging at night to sit at the burrow mouth and ambush passing prey, and they bask by day at the entrance.
An ancient body plan
Superficially the tuatara is a stout, spiny, olive-grey lizard shape, with a crest of soft spines down the neck and back (the name is Māori for “peaks on the back”). But the details set it apart: a rigid, double-arched skull, a unique double row of upper teeth that are simply serrations of the jaw bone rather than replaceable teeth, no eardrums, and a well-formed parietal “third eye” on the crown.
Tuatara are also built for the cold. They remain active at body temperatures as low as 5–7 °C, lower than almost any other reptile, which suits New Zealand’s cool, temperate climate but makes everything they do — growing, digesting, breeding — very slow.
Life at a crawl
A tuatara may take 10 to 20 years to mature and continues growing for decades. Females breed only once every two to five years, and a clutch of around 6 to 12 soft-shelled eggs, buried in an open sunny patch of soil, takes 11 to 16 months to hatch — one of the longest incubation periods of any reptile. As in many reptiles, nest temperature sets the hatchlings’ sex, with warmer nests producing males, which makes the species sensitive to a warming climate.
Threats and conservation
Listed as Least Concern thanks to large island populations and active management, the tuatara is nonetheless entirely dependent on predator control. The Pacific rat (kiore) alone can eliminate a tuatara population by eating eggs and young, and where rats have been removed, hatchling survival rebounds. Conservation work centres on eradicating rodents from islands, breeding tuatara in captivity, and translocating animals to new predator-free sites, including fenced mainland sanctuaries where New Zealanders can see them again after a gap of more than a century.
Tuatara: common questions
Is a tuatara a lizard?
No, though it looks like one. Tuatara are the only living members of the Rhynchocephalia, a reptile order that split from the lizard-and-snake lineage over 240 million years ago, before the first dinosaurs. Anatomical differences include a distinctive skull with two complete bony arches, a unique tooth arrangement — a single row in the lower jaw closing between two rows in the upper — no external ears, and no male copulatory organ.
Does the tuatara really have a third eye?
Yes, a genuine parietal eye on the top of the head, complete with a lens, a primitive retina, and a nerve connection to the brain. It is clearly visible as a pale patch in hatchlings and becomes covered by scales and pigment within a few months. It cannot form images but detects light and probably helps regulate daily and seasonal cycles and vitamin D production. Several other reptiles, amphibians, and fish have one, but the tuatara's is among the best developed.
How long do tuatara live?
A very long time. They grow slowly, do not reach breeding age until 10–20 years old, and keep growing until around 35. Wild individuals of 60 to 100 years are documented, and a captive male named Henry at Southland Museum in New Zealand fathered offspring at an estimated age of about 111. Their slow, cool-running metabolism is thought to be the reason.
Why do tuatara only live on islands now?
They were once widespread across mainland New Zealand, but the arrival of people brought predators the tuatara never evolved with — especially the Pacific rat, which eats eggs and hatchlings. Tuatara were wiped out on the mainland and survived only on rat-free offshore islands. Rat eradication programmes and predator-proof fences have since allowed tuatara to be returned to some islands and mainland sanctuaries.