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Posted by on Dec 10, 2016 in Tell Me Why |

What Is a Tuatara?

What Is a Tuatara?

The tuatara is the only survivor of the beak-headed order of reptiles, called Rhynchocephalia that goes back to the time of the dinosaurs. Their name derives from the Māori language, and means “peaks on the back”. It hunts by night and preys on insects. Like the coelacanth, a prehistoric fish that still survives, the tuatara is almost a living fossil. It can now be found only on some of the small islets off the coast of New Zealand, having been exterminated from the mainland. It basks in the sun during the day and burrows into the soil for safety.

The single species of tuatara is the only surviving member of its order, which flourished around 200 million years ago. Their most recent common ancestor with any other extant group is with the squamates (lizards and snakes). For this reason, tuatara are of great interest in the study of the evolution of lizards and snakes, and for the reconstruction of the appearance and habits of the earliest diapsids, a group of amniote tetrapods that also includes dinosaurs, birds, and crocodilians.

Tuatara are greenish brown and gray, covered in scales and measures up to 80 cm (31 in) from head to tail-tip and weigh up to 1.3 kg (2.9 lb) with a spiny crest along the back, especially pronounced in males. Their dentition, in which two rows of teeth in the upper jaw overlap one row on the lower jaw, is unique among living species. They are even more unusual in having a pronounced photoreceptive eye, the “third eye”, which is thought to be involved in setting circadian and seasonal cycles. They are able to hear, although no external ear is present, and have a number of unique features in their skeleton, some of them apparently evolutionarily retained from fish.

Although tuatara are sometimes called “living fossils”, recent anatomical work has shown that they have changed significantly since the Mesozoic era. While mapping its genome, researchers have discovered that the species has between five and six billion base pairs of DNA sequence.

tuatara Sphenodon punctatus

The tuatara Sphenodon punctatus has been protected by law since 1895. A second species, S. guntheri, was recognized in 1989 but since 2009 its use has been discontinued. Tuatara, like many of New Zealand’s native animals, is threatened by habitat loss and introduced predators, such as the Polynesian rat (Rattus exulans). They were extinct on the mainland, with the remaining populations confined to 32 offshore islands, until the first mainland release into the heavily fenced and monitored Karori Sanctuary in 2005.

During routine maintenance work at Karori Sanctuary in late 2008, a tuatara nest was uncovered, with a hatchling found the following autumn. This is thought to be the first case of tuatara successfully breeding on the New Zealand mainland in over 200 years, outside of captive rearing facilities.

Tuatara feature in a number of indigenous legends, and are held as ariki (God forms). Tuatara is regarded as the messenger of Whiro, the god of death and disaster, and Māori women are forbidden to eat them. Tuatara also indicate tapu (the borders of what is sacred and restricted), beyond which there is mana, meaning there could be serious consequences if that boundary is crossed.

Māori women would sometimes tattoo images of lizards, some of which may represent tuatara, near their genitals. Today, tuatara is regarded as a taonga (special treasure).

Content for this question contributed by Kathy Misuir, resident of Roselle Park, Union County, New Jersey, USA