Tuatara are members of the taxon Rhynchocephalia and are most closely related to squamates (i.e., amphisbaenians, lizards, and snakes). Like squamates, tuatara are elongate and shed skin in large fragments. Unlike squamates, tuatara lack paired hemipenes (male copulatory organs).

The common name "tuatara" comes from Maori words meaning "spines on back," in reference to the crest on the backs of males and females. Tuatara have a lizard-like appearance: both groups are elongate with four limbs (most lizards) and both lizards and tuatara are known to shed their tails (caudal autotomy). The groups diverge, however, on the presence or lack of a paired hemipenes, the morphology of the teeth and skull, and other important features. Tuatara are long-lived species, reaching sexual maturity at about 20 years. Two species of tuatara, Sphenodon guntheri and Sphenodon punctatus, are located in New Zealand, and are the only species known to exist.

The two recognized species of tuatara (Sphenodon punctatus and Sphenodon guntheri) are found on approximately 30 small, relatively inaccesible, islands off the coast of New Zealand. The species was once widely distributed throughout New Zealand, but became extinct on the mainland before the arrival of European settlers.

Biogeographic Regions: australian (Native )

Tuataras may be grey, olive, or brickish red in color. They range in adult length from about 40 cm (female) to 60 cm (large male), with the male generally reaching larger proportions. They lack external ears, have a diapsid skull (two openings on either side), and posess a "parietal eye" on the top of their head. Other lizards also have this "third-eye," which contains a retina and is functionally similar to a normal eye, though the function has not been clearly recognized and a scale grows over it in adult tuataras. The male tuatara displays a striking crest down the back of the neck, and another down the middle of the back. The female has a less developed version of this. Unlike all other living toothed reptiles, the tuatara's teeth are fused to the jaw bone (acrodont tooth structure). The tuatara has a very slow metabolism and is a very long-lived species. It's not uncommon for an individual to live for over 100 years.

Range mass: 0.4 to 1 kg.

Average basal metabolic rate: 0.0605 W.

The geographic range which the tuatara inhabits is a difficult niche for any species, particularly a reptile. The islands are generally cliff-bound, frequently exposed to strong winds, and support a natural, often stunted, vegetation of salt and wind tolerant species. Most islands are also home to several species of sea birds, whose nutrient-rich guano helps support the island's ecosystem. The habitat is cold and damp, with temperatures rarely exceeding 70 degrees Fahrenheit, and a humidity level of about 80 percent. The temperature may often approach freezing, but the tuatara is able to maintain normal activities at temperatures as low as 45 degrees Fahrenheit. Preferred body temperature is between 60 and 70 degrees, this is the lowest optimal body temperature of all reptiles. At temperatures above 76 degrees, tuataras show signs of distress, and most will die if the temperature exceeds 82 degrees.

Terrestrial Biomes: chaparral

• Terrestrial

Diet consist of arthropods, earthworms, snails, bird eggs, small birds, frogs, and lizards, and a native cricket-like insect the size of a mouse called a weta. Young tuataras are also occasionally cannibalized. Due to its low metabolic rate, the tuatara eats much less frequently than other reptiles.

Animal Foods: birds; amphibians; reptiles; eggs; insects; terrestrial non-insect arthropods; mollusks; terrestrial worms

Primary Diet: carnivore (Insectivore )

Average lifespan

Status: captivity: 35.0 years.

Average lifespan

Status: captivity: 77.0 years.

Average lifespan

Status: captivity: 50.0 years.

Average lifespan

Status: captivity: 11.7 years.

Average lifespan

Sex: male

Status: captivity: 7.0 years.

It takes between 10 and 20 years for a tuatara to reach sexual maturity. The female, on average, lays between 5 and 18 eggs only once every 4 years, the longest reproductive cycle of any reptile. Mating occurs from mid-summer to early autumn (January-March) and the eggs are laid the following spring or early summer (October-December). Incubation takes from 12 to 15 months, with the development of the embryo stopping during the winter months. Thus, a hatchling tuatara would have been conceived over two years earlier. The male is devoid of any external sex organs, and copulation is achieved by a meeting of the cloacal regions in what is known as a "cloacal kiss."

Average age at sexual or reproductive maturity (male)

Sex: male: 4380 days.

Average age at sexual or reproductive maturity (female)

Sex: female: 4380 days.

In 1895, the country of New Zealand awarded the tuatara strict legal protection. It is currently considered a CITES (Convention on the International Trade in Endangered Species) Appendix I species. This is the most restricted classification for a species. In order for a zoo to possess this species, very demanding rules must be followed, and the public display of tuataras has only recently been allowed. Access to the islands that the tuatara inhabit is strictly regulated, and for many years no tuataras have been removed from any island for any reason.

US Federal List: endangered

CITES: appendix i

IUCN Red List of Threatened Species: lower risk - least concern

None known.

Not known.