Tuatara have a scaly loose skin which is soft to the touch. They have a variable body temperature which enables them to survive in cold climates. They live in burrows and are nocturnal, hunting at night just outside their burrow entrance. They feed on wetas, worms, lizards, millipedes and small seabirds.

An adult can grow up to 24cm in length and weigh about 500 grams. Tuatara breed only every two to four years. Tuatara lay about a dozen leathery shelled eggs between October and December. The eggs are burrowed and then abandoned. After about 12-15 months the eggs hatch, the young using an egg tooth to break out of their shells. From the start, baby tuatara take care of themselves, but are very vulnerable to predation. Tuatara mature at about 13 years old and may live to be 60 years old.

There are two species of tuatara. The most common species is Sphenodon punctatus, the tuatara which is found on the Northern Islands. It is thought that the Cook Strait Islands tuatara is a subspecies of the Northern tuatara. S.punctatus has a brown-white appearance. The second species is the Brothers tuatara Sphenodon guntheri which is unique to Brothers Island and has an olive skin with yellow spots.