Tuataras are reptiles that used to live all over New Zealand's main islands.
Now, tuataras are endangered.
Mammals introduced by humans to New Zealand, such as dogs, cats, and rats, have eaten many young tuataras and tuatara eggs.
Habitat destruction has also reduced the tuatara population.
Today, tuataras can only be found only on about 30 small, islands off the coast of New Zealand - where there are no mammal predators - or in sanctuaries.
Although tuataras resemble lizards superficially, they are not lizards.
Tuataras belong to the genus Sphenodon, which is the only living genus in the family Sphenodontidae, and in the order Sphenodontia.
They are more closely related to squamates (snakes and lizards) than to any other animal.
Squamates and tuataras share a common ancestor and together make up the clade known as lepidosaurs - reptiles with overlapping scales.
A clade is a group of organisms all of whom share a common ancestor. All of the descendants of that ancestor belong to the clade.
There were once many species of Sphenodontia, but almost all of them became extinct around 60 million years ago.
Scientists have identified just two species of tuatara that are alive today: Sphenodon punctatus, of which there are two subspecies - the Cook Strait tuatara and the Northern tuatara - and Sphenodon guntheri, the Brothers Island tuatara.
Recent DNA research suggests that Sphenodon punctatus and Sphenodon guntheri may actually be a single species.
Tuataras may be olive, grey or brick red, with white or yellow spots.
They are about 30 inches long from their heads to the tips of their tails and weigh about one or two pounds.
Males are larger than females.
A tuatara has a crest of spines along its back. This crest is more noticeable in males than in females.
The name "tuatara" is Maori for "peaks on the back".
A tuatara can move each of its eyes independently.
Tuataras have two rows of teeth in their upper jaws, but only one in their lower jaws. When a tuatara closes its mouth, the bottom row of teeth fits in between the two upper rows.
A tuatara's teeth are fused to its jawbone and cannot be replaced once they wear down.
This means that very old tuataras must eat with just their gums.
A tuatara has a light-sensitive organ known as a parietal eye, third eye, or pineal organ on the top of its head. The parietal eye has a retina, a cornea, and a small lens. The parietal eye may help to set circadian (daily) and seasonal biological rhythms and help to regulate body temperature.
The parietal eye is visible in hatchlings. In adults, it is covered with opaque scales and is hard to see.
Tuataras do not have external ears, but they can hear.
They have lower body temperatures than any other reptile.
A tuatara's optimal body temperature is between 61 and 70 degrees Fahrenheit (16 and 21 degrees Celsius).
It will remain active at temperatures as low as 41 degrees Fahrenheit (5 degrees Celsius) and will usually die if the temperature goes above 82 degrees Fahrenheit (28 degrees Centigrade).
Because of their low body temperatures, tuataras have very slow metabolisms.
Tuataras grow very slowly and have long lifespans - 60 years on average. Some tuataras live for over 100 years.
It takes a tuatara 10 to 20 years to reach sexual maturity.
In 2009, Henry, a 111-year old tuatara at Southland Museum and Art Gallery in Invercargill, New Zealand, became a father for the first time.
Tuataras can be found in forests and grasslands near colonies of seabirds, such as petrels.
They live in burrows, which have often already been dug by birds.
Tuataras are territorial. When males fight over territory, they raise their crests. The skin between their shoulders and crests darkens.
A tuatara's diet includes invertebrates - such as insects, spiders, worms and slugs - as well as frogs, lizards, young birds, birds' eggs, lizards and young tuataras.
A popular food item for the tuatara is the weta, a large insect that resembles a cricket.
Older tuataras, whose teeth are very worn or have completely worn away, can only eat soft foods, such as worms or slugs.
Adults are nocturnal (active at night), but hatchlings are diurnal (active during the day). This probably helps them to avoid being eaten by cannibalistic adults.
On sunny days, adults will come out of the burrows to bask in the sun.
Tuataras hibernate in winter.
Tuataras are oviparous (lay eggs)
Mating takes place only about once every four years, and occurs in February and March.
A male will raise his crest as part of the mating ritual.
Male tuataras do not have penises.
During mating, the male lifts the female's tail and places his cloaca (a hole that is used for both excretion and reproduction) over her cloaca. Sperm is then transferred from the male's cloaca to the female's cloaca.
Between October and December, the female lays from 7 to 20 eggs in an underground nest, which she builds.
Eggs take between 12 and 15 months to hatch. Embryos stop developing during the winter.
The temperature of the egg determines whether the hatchling will be male or female. Male tuataras tend to come from warmer eggs, and female tuataras tend to come from cooler eggs.
Climate change is a threat to the tuatara population. If the climate becomes too warm, only males will be born, and tuataras will not be able to reproduce.
Parents do not care for the young.