Overview
The Brothers Island Tuatara (Sphenodon guntheri) is an extraordinary reptilian relic endemic to the rugged Cook Strait region of New Zealand. Representing one of only two surviving species of the ancient order Rhynchocephalia, which flourished over 200 million years ago alongside early Mesozoic dinosaurs, this ‘living fossil’ survived in the wild exclusively on a tiny four-hectare windswept outcrop known as North Brother Island. Possessing archaic skeletal anatomy, a prominent light-sensitive parietal ‘third eye,’ and extreme metabolic cold tolerance, the tuatara is an irreplaceable window into early vertebrate evolution.
Biology and Physical Characteristics
Unlike true lizards, Sphenodon guntheri exhibits unique physiological and skeletal features preserved from the Triassic period. It possesses a complete diapsid skull with two temporal fenestrae and an unmovable upper jaw, featuring a unique double row of teeth on the upper jaw that shears against a single lower row like a pair of serrated scissors. Juveniles possess a well-developed parietal eye on the crown of the head, complete with a lens, retina, and nerve connection to the brain that regulates circadian thermoregulation. Its olive-brown to yellowish skin is adorned with spiny dorsal crest scales that males erect during territorial displays.
Behavior and Ecology
Brothers Island tuataras thrive at surprisingly low body temperatures, remaining active in ambient conditions between 5°C and 16°C (41°F–61°F) that would immobilize ordinary tropical lizards. They maintain a fascinating commensal relationship with burrowing fairy prions and shearwaters, frequently cohabiting seabird burrows to sleep during cold daylight hours before emerging at night to hunt giant wētā, beetles, and crickets lured by seabird guano. Their metabolism is remarkably slow, with individuals taking up to 15 to 20 years to attain sexual maturity and females producing clutches of 5 to 18 parchment-shelled eggs only once every four years.
Conservation and Human Impact
Extirpated from the New Zealand mainland centuries ago by invasive mammalian predators (particularly Polynesian and European rats), wild Sphenodon guntheri was reduced to fewer than 500 individuals on North Brother Island. Heroic conservation initiatives led by the New Zealand Department of Conservation (DOC) and Victoria University have orchestrated captive incubation, disease screening, and successful reintroductions to pest-free island sanctuaries including Titi and Matiu/Somes islands. Strictly managed biosecurity protocols and rat-eradication campaigns safeguard these precious offshore strongholds.
Interesting Factoid
The tuatara’s heart beats only once every several minutes in cold weather, and it can comfortably hold its breath underwater or in burrows for over an hour without distress.
Last updated: October 2026