Tuatara

• 1. Introduction

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  The tuatara, Sphenodon punctatus, is a reptile found naturally only in New Zealand, and its Māori name means "peaks on the back". On the 23rd of January 2009, a male tuatara named Henry became a father at the Southland Museum in Invercargill. He was 111 years old, and the female he mated with was 80. Most animals are long gone by such ages, which raises a bigger puzzle about this spiny, lizard-shaped creature. Why did scientists file it under the wrong label for decades? What does it share with birds, crocodiles and creatures from the age of dinosaurs? How does it live on cold, remote islands, and why did it vanish from the mainland? And why do Māori traditions treat it as both a messenger and a guardian?

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• 2. Misfiled as a Lizard

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  In 1831 the British Museum received a skull, and John Edward Gray used it to describe a genus he called Sphenodon. The name joins the Greek words for wedge and tooth. Gray took the animal for a lizard. In 1842 he described a living specimen as Hatteria punctata, without realising it was the same kind of animal as the skull. His confusion was understandable. Tuatara and lizards both belong to the superorder Lepidosauria. Both can lose the tip of the tail when threatened, and both have transverse slits for the cloaca.

  The mistake lasted until 1867, when Albert C. L. G. Günther of the British Museum noticed traits resembling those of birds, turtles and crocodiles. He proposed a new order for the tuatara and its fossil relatives, Rhynchocephalia, meaning "beak head". Since 1869 the species has carried the name Sphenodon punctatus, with punctatus being Latin for spotted.

  The order's name caused trouble of its own. At one point taxonomists dumped many unrelated species into Rhynchocephalia, creating what they call a wastebasket taxon. In 1925 Williston proposed Sphenodontia for only the tuatara and its closest fossil kin. Rhynchocephalia is the older name and is still widely used. Many scholars treat Sphenodontia as a subset covering almost the whole order except its most primitive members.

  The count of living species has shifted too. Two were once recognised. One was the northern tuatara. The other was the rarer Brothers Island tuatara, called guntheri in honour of Günther and found on North Brother Island in Cook Strait. A 2009 paper re-examined the genetic evidence and concluded that these were geographic variants. One species remains, with two subspecies. The Brothers Island animal is olive brown with yellowish patches and considerably smaller. The northern animal ranges from olive green through grey to dark pink or brick red, usually mottled and always with white spots. Yet jaw shape could not separate Brothers Island individuals from other modern and fossil samples.

  A third name belongs to history. In November 1885 William Colenso was sent an incomplete subfossil specimen from a coal mine and called it Sphenodon diversum. In 1970 Fawcett and Smith judged it a synonym of the subspecies, because nothing set it apart.

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• 3. Deep Time

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  Around 244-241.5 million years ago, in the Middle Triassic, the first rhynchocephalians appear in the fossil record. The earliest known is Agriodontosaurus, found in England. During the Late Triassic the group diversified greatly. By the Jurassic it was the world's dominant group of small reptiles, with forms such as the aquatic pleurosaurs and the plant-eating eilenodontines.

  The tuatara's own branch, Sphenodontinae, shows up in the Early Jurassic of North America around 190 million years ago. Those earliest members already looked very much like the modern animal. Then the group declined through the Cretaceous, possibly because of competition with mammals and lizards. Outside New Zealand, the youngest record is Kawasphenodon from southern Patagonia, dated to roughly 66-60 million years ago in the early Paleocene. It may itself be a sphenodontine.

  New Zealand holds a later chapter. The Saint Bathans fauna of Otago, from roughly 19-16 million years ago in the early Miocene, includes fossils probably from a close relative of the tuatara. They are too incomplete to place in the genus Sphenodon with certainty. Even so, they suggest that the ancestors were already living in New Zealand before it separated from Antarctica, around 82-60 million years ago.

  Tuatara are sometimes called living fossils, and paleontologists now discourage the term. The animal keeps the body plan of its Mesozoic ancestors from 240-230 million years ago. But no unbroken fossil record shows that the species itself has survived unchanged since then. Its closest living relatives are the squamates, the lizards and snakes.

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• 4. A Body Built Differently

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  Adult males measure 61 cm and females 45 cm, which makes tuatara the largest reptiles in New Zealand. The San Diego Zoo cites lengths of up to 80 cm. Males weigh up to 1 kg and females up to 0.5 kg, while Brothers Island animals reach about 660 g. Their greenish brown colour matches their surroundings and can change over a lifetime. Adults shed their skin at least once a year, and juveniles do so three or four times. The spiny crest down the back is made of soft triangular folds of skin. Males have the larger crest and can stiffen it for display.

  The skull is built differently from a lizard's. Unlike most lizards, a tuatara has a complete lower temporal bar, formed when bones behind the eye socket fuse. Earlier rhynchocephalians had an open gap there, so the closed bar is a later development. It is thought to steady the skull during biting. The teeth are attached to the top edge of the jaw and fused so tightly that the boundary with the bone is hard to see. They have no roots and are never replaced. Some people claim tuatara have no true teeth, but microscopic study shows enamel, dentine and pulp cavities. A second row of teeth grows from the roof of the mouth, and the lower teeth slot between the two upper rows. The jaw can then slide forward, shearing through chitin and bone. As the teeth wear, older animals turn to softer prey such as earthworms, larvae and slugs. Eventually they chew with smooth jaw bones alone.

  Further back, the skeleton keeps features lost in most living animals. A pair of triangular proatlas bones sits between the first neck vertebra and the skull. The vertebrae are hourglass-shaped, concave at both ends, a pattern unique among living amniotes. Rib-like gastralia protect the belly, and the true ribs carry small hooked projections that birds also have. The tuatara is the only living tetrapod with both well-developed gastralia and these projections. The brain fills only half of the space inside the skull, a ratio once used to estimate the brain size of dinosaurs. Birds, which are living dinosaurs, have brains that fill far more of that space, so the comparison is shaky.

  The senses are just as unusual. The eyes can focus independently and have a reflective layer that helps vision in the dark. Five visual opsin genes hint at good colour vision, perhaps even in dim light. On top of the head, hatchlings have a translucent patch covering a parietal eye with its own lens and a retina. After four to six months, opaque scales and pigment cover it. It can detect light but probably not movement or images, and likely helps regulate the daily rhythm, seasonal changes and body temperature. No other living tetrapod has a more pronounced one.

  Hearing is primitive. There is no eardrum and no earhole, and fat fills the middle ear. Still, tuatara respond to sounds between 100 and 800 Hz, with peak sensitivity at 200 Hz. The sense of smell relies on around 472 odorant receptors, a number closer to birds than to turtles and crocodiles.

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• 5. Cold and Slow

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  Temperature rules the tuatara's life. Adults are nocturnal and terrestrial but often bask in the sun. Hatchlings hide under logs and stones and are active by day, probably because adults are cannibalistic. The optimal body temperature is 16-21 °C, the lowest of any reptile. Tuatara stay active at temperatures as low as 5 °C and hibernate in winter. Temperatures over 28 °C are generally fatal. A low body temperature means a slow metabolism.

  On their islands they share ground with burrowing seabirds such as petrels, prions and shearwaters. Tuatara shelter in the birds' burrows or dig their own. Seabird guano supports the beetles, crickets, spiders, wētās, earthworms and snails they mostly eat. They also take frogs, lizards, eggs and chicks, and in summer they feed mainly on fairy prions and their eggs. Feeding attempts were observed in light as dim as under 0.0125 lux. Both sexes defend territories, and their bite can cause serious injury. A specialised parasite, the tuatara tick Archaeocroton sphenodonti, lives on them and favours larger males, who roam widely and meet rivals often.

  Reproduction is the slowest of any reptile. Tuatara take 10 to 20 years to mature, mate in midsummer, and females lay eggs once every four years. A courting male darkens his skin, raises his crest and circles the female on stiffened legs. Males have no penis. Instead the male presses his vent against hers in what is sometimes called a cloacal kiss. Even so, their sperm swim two to four times faster than any reptile sperm studied earlier. A female needs between one and three years to provision the eggs with yolk. Forming the 0.2 mm shell takes up to seven months. Hatching comes 12 to 15 months after mating. Some females guard eggs for up to 10 days. The main threat is other females, who may dig up an earlier brood while seeking a nest site.

  The temperature of the egg decides the sex. At 21 °C the odds are even. At 22 °C about 80% are male, at 20 °C about 80% are female, and at 18 °C every hatchling is female.

  Growth is slow too, continuing for the first 35 years. The average lifespan is about 60 years, and tuatara can pass 100. Some experts think captive animals might reach 200. Researchers point to 26 genes for selenoproteins, which in humans handle antioxidant defence, as one possible reason. Their genome holds five to six billion base pairs, nearly twice the human total. Among reptiles, only the Greek tortoise has a larger one. Of its CpG sites, 81% are methylated, against 78% in zebrafish and 70% in humans.

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• 6. Vanishing From the Mainland

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  The tuatara has been protected by law since 1895, and New Zealand's Wildlife Act 1953 protects it absolutely. It is also listed under Appendix I of CITES, which prohibits commercial international trade in wild-sourced specimens. Yet protection came after a long retreat. Subfossil remains in sand dunes, caves and Māori middens show tuatara once lived across the North and South Islands. They were wiped out there before European settlement and survived on 32 offshore islands free of mammals.

  The islands themselves offer a clue. They are hard to reach, and few animals have colonised them. That suggests some animal missing from the islands may have driven the tuatara from the mainland. Then kiore, the Polynesian rat, became established on several of them. Tuatara persisted there but did not breed, and they were much rarer. Before conservation work began, a quarter of the distinct populations had died out. The total today is estimated at 60,000 to 100,000.

  Climate change adds a new risk. Because incubation temperature sets the sex, warming could skew the ratio of males to females. The solutions on offer are the selective removal of adults and the incubation of eggs.

  Rat removal has produced the clearest gains. Tuatara were taken off Stanley, Red Mercury and Cuvier Islands in 1990 and 1991 so the rats could be eradicated. All three groups bred in captivity and returned home with their new juveniles. Little Barrier Island held only eight tuatara in the 1991-92 season. Females in captivity there produced 42 eggs, which were incubated at Victoria University, and the offspring were released in 2006 after rats were cleared.

  Results vary by island. In the Hen and Chicken Islands, rats were eradicated on Whatupuke in 1993, Lady Alice Island in 1994 and Coppermine Island in 1997. Juveniles have been seen again on those three. On Hen Island rats remain, and as of 2001 no juvenile tuatara had been seen there.

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• 7. Rescue and Return

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  Moving animals has been a second strategy. The Brothers Island tuatara lives naturally on one small island, with about 400 animals. In 1995-50 juveniles and 18 adults went to Titi Island in Cook Strait. Two years later more than half had been seen again, and all but one had gained weight. In 1998 captive-bred juveniles and wild-caught adults, 34 and 20, were sent to Matiu/Somes Island in Wellington Harbour, where the public has easier access. In late October 2007-50 tuatara hatched from North Brother Island eggs were released on Long Island in the outer Marlborough Sounds. They had spent five years at Wellington Zoo in a secret enclosure off display. A separate group lives off display at the San Diego Zoo in Balboa, with no successful breeding reported so far.

  The northern tuatara occurs naturally on 29 islands and numbers over 60,000. In 1996-32 adults moved from Moutoki Island to Moutohora, which could hold an estimated 8,500 and might allow public viewing. In 2003-60 were introduced to Tiritiri Matangi Island, where visitors sometimes see them sunbathing. A further 432 juveniles raised at Victoria University were prepared for release on the Rangitoto Islands in 2004, after rodents were cleared there.

  The biggest step came on the mainland. In 2005 tuatara were released into the heavily fenced Zealandia sanctuary, then called Karori Wildlife Sanctuary. In October 2007, 130 more arrived from Stephens Island. During maintenance work in late 2008, a nest was uncovered, and a hatchling turned up the following autumn. It is thought to be the first successful wild breeding on the North Island in over 200 years.

  Captive breeding supports all of this. The first success is believed to belong to Sir Algernon Thomas, either at his university offices or residence on Symonds Street in the late 1880s, or at his home in Mount Eden in the early 1890s. The Southland Museum and Art Gallery in Invercargill began the first institutional programme in 1986. At Auckland Zoo in the 1990s, it was discovered that tuatara have temperature-dependent sex determination. Hamilton, Auckland and Wellington zoos breed tuatara for release, and in January 2016 Chester Zoo in England announced the first captive breeding outside New Zealand.

  Henry's own family story fits here. In January 2009 all 11 eggs laid by his mate Mildred hatched. Henry had needed surgery to remove a cancerous tumour before he could breed.

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• 8. Guardian of Knowledge

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  In Māori tradition, tuatara appear in a number of legends and are held as ariki, or god forms. They are regarded as messengers of Whiro, the god of death and disaster, and Māori women are forbidden to eat them. Tuatara also mark tapu, the border of what is sacred and restricted. Beyond that border lies mana, and crossing it could bring serious consequences. Māori women sometimes tattooed images of lizards, some perhaps representing tuatara, near their genitals.

  Today tuatara are regarded as a taonga, a special treasure, and as kaitiaki, guardians of knowledge. The animal also moved into modern national life. It was pictured on one side of the New Zealand five-cent coin, phased out in October 2006. Its name also went to a journal. The Journal of the Biological Society of Victoria University College, later Victoria University of Wellington, ran from 1947 until 1993. The New Zealand Electronic Text Centre at the same university has since digitised it.

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