Often referred to as 'living fossils' because they are the only surviving members of the rhynchocephalid reptiles, tuataras are in fact very advanced.

Meaning of scientific name
Sphenodon = "wedge-toothed". Punctatus = "spotted"

Life span
Tuatara live at least 35 years and possibly as long as 60.

Statistics
Total length: males: 60cm; females: 50cm. Weight: males: 1300g; females: 550g.

Physical Description
Although they look superficially like an iguana, tuatara are not lizards. A quick look shows that they lack external ears. They vary in colour from olive to grey, and sometimes even chestnut. Males are bigger and heavier than females, and have conspicuous spiny crests running along their neck and back. The famous 'third eye' is an organ known as the pineal, which has its own lens and retina, but is covered over by opaque scales and difficult to see in adults. The second tuatara species (the North Brother Island tuatara) looks very similar, but has considerable genetic differences.

Distribution
Tuatara used to range throughout both the main islands of New Zealand, but today are restricted to 30 small islands. The rarer species of tuatara, Sphenodon guntheri, is only found on North Brother Island.

Habitat
Tuatara inhabit forest and pasture near seabird colonies. The preferred habitat is coastal broad-leaf forest, especially where seabirds have dug burrows.

Diet
Most of the tuatara diet is insects and other terrestrial invertebrates. They also consume lizards, and will even eat their own young. Small burrow-nesting seabirds like petrels are also eaten: eggs and chicks as well as adults.

Behaviour
Adult tuatara are mainly nocturnal, although they will come to the entrance of their burrows to bask on sunny days. Unlike most reptiles, they can stay relatively active as their body temperatures drop - activity not completely ceasing until they are at a temperature of 7 degrees centigrade. Juvenile tuatara are more active in the daytime, possibly because of the danger of cannibalism by adults. Tuatara are mostly sit-and-wait predators, staying still and then grabbing prey that comes near. Although tuatara can dig their own burrows, they often use the burrows of petrels to live in. Like lizards, tuatara can shed their tails and regrow them. Males often lose their tails in fights during the breeding season.

Reproduction
Males establish territories in late summer or autumn (January to March) and display to attract females and dissuade rivals. Mating takes place in February and March, and 7 to 10 eggs are laid in October to December in an underground nest dug by the female. After laying her eggs, she abandons them. Tuatara eggs have a very long incubation period, taking 12 to 15 months to hatch, because development of the embryo ceases altogether during the winter. Tuatara are the only living reptiles in which the males have no penis.

Conservation status
This species is not listed by the IUCN (but the North Brother Island tuatara is classed as Vulnerable).

Notes
The function of the tuatara’s 'third eye' or pineal gland is unclear. In lizards the pineal organ is used in regulating body temperature. In mammals the pineal measures day length and controls the onset of seasonal behaviour (breeding, hibernation, etc). Tests have so far failed to uncover the function of the pineal in the tuatara. Tuatara are known as living fossils because of the very similar species that lived in the Jurassic - for instance Homoeosaurus. However, although they have many primitive features, tuatara have not remained unchanged for 200 million years.