Each Tuesday I write a simple and short piece about an awesome reptile. This time, the reptile of the week is the Tuatara. The word “tuatara” comes from the Māori language, meaning “peaks on the back”. The animal was first described by British zoologist John Edward Gray in 1831.

The Tuatara actually consists of two species, both found in New Zealand. They are classed as Threatened (Vulnerable) on the IUCN list. Populations have been affected mostly by habitat loss due to humans and introdicution of terrerstrial mammals to the island by humans. They are greenish brown, and measure about 70-80 cm in length. They are impressive looking animals, with spines down their back which gives them their name. However, as you will discover, this animal possesses many traits which are a lot more surprising.

When the British Museum received a skull of this animal, it was officially described as a lizard. This seemed like a fair choice, as it doesn’t stand out as a snake, crocodile, turtle or tortoise. But the museum didn’t realize quite how important the find was, as this animal is not a lizard. A creationist may describe it as the lizard “kind”, but in reality snakes are more closely related to lizards than these little guys are.

Although the Tuatara appears to be a lizard, it belongs to a completely distinct lineage, the order Sphenodontia. The Tuatara, and the rarer Sphenodon guntheri, are the only surviving members of the entire order, which was a successful and flourishing order 200 million years ago. Scientists are fascinated with the Tuatara as its most recent common ancestor with any other extant group is with the squamates – the lizards and snakes. It is hoped that studying this animal can help provide clues about the evolution of lizards, snakes, birds and crocodiles.

The Tuatara belong in a sistergroup to the Squamata which includes the snakes and lizards. There are a few characters which are shared between the two including a transverse cloacal slit and the loss of part of the tail when stressed/threatended. The Tuatara looks like a lizard, but this is similar to the way a dolphin looks like a fish. Even most of the very earliest amniotes resembled lizards. Even the oldest known fossil reptile superficially resembles a modern lizard. However, this is where the similarities end and the Tuatara possesses some entirely unique characteristics in the reptile world.

The Tuatara has two rows of teeth on the upper jaw and these perfectly overlap one row of teeth on the lower jaw, and this arrangement is unique among living species. They also possess something quite remarkably: a third eye. This third eye only appears in hatchlings and is then lost as the animal grows, but the eye itself consists of a lens and retina etc. Tuataras are able to hear perfectly well despite having no external ear. Their skeletons also have some rather unique characterists, some of which seem to be characterists retained from fish.

It is known as the most unspecialised living amniote. The animal’s brain, heart and mode of locomotion resembles that of amphibians and they possess features that are the most primitive of any reptile alive today. In most diapsids, the skull has evolved considerably over the last 200 million years and many characteristics have been lost, but the Tuatara still retains many of them, including an upper jaw that is still strongly attached to the skill.

The Tuatara also has a special third eyelid on each eye, specialist visual cells for both day and night vision, and a tapetum lucidum which reflects onto the retina to aid in night vision. On the top of the head is the third eye or “parietal eye”. This third eye has a lens, cornea, retina and degenerated nerve-connection to the brain which provides evidence that it evolved from what was once a real eye. Although the Tuatara shows a frequency response between 100-800 Hz, the hearing organs are extremely primitive with no ear opening or even ear drum.

1 = premaxilla, 2 = nasal, 3 = prefrontal, 4 = frontal, 5 = maxilla, 6 = postfrontal, 7 = dentary, 8 = postorbital, 9 = jugal, 10 = parietal, 11 = squamosal, 12 = quadrate

The spine of the tuatara is made of hour-glass shaped amphicoelous vertebrae, that are usually only found in fish and some amphibians. The Tuatara is the only reptile known to possess this character. Many parts of the body such as the pelvic and shoulder girdles, the ribs and even the scales are arranged differently than in any of the lizards.

The Tuatara also has a much lower body temperature than any lizards, and slower metabolism. Because of this, they take a very long time to reach sexual maturity, taking ten years! They don’t have a penis, and instead the male lifts the tail of the female and places his vent over hers. The process is much the same as it is in modern birds. The eggs are very soft and take years for the mother to produce. These are very long-lived animals due to their extremely slow growth rate. At the Southland Museum and Art Gallery, they have a male named Henry who is still sexually active at the grand age of 112 years old! What a trooper.

Being among the only two species now existing for an entire order of organisms, they are now watched very carefully and captive breeding projects are in place. One of the main problems has been the introduction of Polynesian rats by humans. In 1990, the Tuataras were removed from several of the islands so that rat eradication could begin. The removed populations bred well in captivity. Once the rats were gone, the Tuataras and their captive-bred young were reintroduced. They are fascinating animals to have around as we can learn a lot from them. But we must be careful or we could be responsible for losing the remainder of an entire order in a few short years.