Tuatara

Relationships of the tuatara to other living reptiles and birds, after Simões et al. 2022 }}}}}}}} Tuatara, along with other now-extinct members of the order Rhynchocephalia, belong to the superorder Lepidosauria, as do the order Squamata, which includes lizards and snakes. Squamates and tuatara both show caudal autotomy (loss of the tail-tip when threatened), and have transverse cloacal slits. Tuatara were originally classified as lizards in 1831 when the British Museum received a skull. John Edward Gray used the name Sphenodon to describe the skull; this remains the current scientific name for the genus. Sphenodon is derived from the Greek for "wedge" (σφήν, σφηνός/sphenos) and "tooth" (ὀδούς, ὀδόντος/odontos). In 1842, Gray described a member of the species as Hatteria punctata, not realising that it and the skull he received in 1831 were both tuatara. The genus remained misclassified as a lizard until 1867, when Albert C. L. G. Günther of the British Museum noted features similar to birds, turtles, and crocodiles. He proposed the order Rhynchocephalia (meaning "beak head") for the tuatara and its fossil relatives. Since 1869, Sphenodon punctatus (or the variation Sphenodon punctatum in some earlier sources) has been used as the scientific name for the species. Williston in 1925 proposed the Sphenodontia to include only tuatara and their closest fossil relatives. The earliest rhynchocephalian, Agriodontosaurus, is known from the Middle Triassic (Anisian) of England, around . During the Late Triassic, rhynchocephalians greatly diversified, when the group was represented by a diversity of forms, including the aquatic pleurosaurs and the herbivorous eilenodontines. Rhynchocephalians declined during the Cretaceous period, possibly due to competition with mammals and lizards, Fossil material that can be referred to as sphenodontine is known from the early Miocene (c. 19–16 million years ago) Saint Bathans fauna of Otago in the South Island of New Zealand. Whether these specimens are referable to the genus Sphenodon proper is not entirely clear due to their incomplete nature, but they are likely to be from a taxon that is closely related to tuatara. Therefore, the ancestors of the tuatara were likely already present in New Zealand prior to its separation from Antarctica around 82–60 million years ago. Cladogram of the position of the tuatara within Sphenodontia, after Simoes et al., 2022: The specific name punctatus is Latin for "spotted", and guntheri refers to German-born British herpetologist Albert Günther. A 2009 paper re-examined the genetic bases used to distinguish the two supposed species of tuatara, and concluded they represent only geographic variants, and only one species should be recognised. Consequently, the northern tuatara was re-classified as Sphenodon punctatus punctatus and the Brothers Island tuatara as Sphenodon punctatus guntheri. The Brothers Island tuatara has olive brown skin with yellowish patches, while the colour of the northern tuatara ranges from olive green through grey to dark pink or brick red, often mottled, and always with white spots. In addition, the Brothers Island tuatara is considerably smaller. However, individuals from Brothers Island could not be distinguished from other modern and fossil samples on the basis of jaw morphology. An extinct species of Sphenodon was identified in November 1885 by William Colenso, who was sent an incomplete subfossil specimen from a local coal mine. Colenso named the new species S. diversum. Fawcett and Smith (1970) consider it a synonym to the subspecies, based on a lack of distinction. ==Description==

Tuatara are the largest reptiles in New Zealand. Adult S. punctatus males measure in length and females . Males weigh up to , and females up to . The tuatara's greenish brown colour matches its environment, and can change over its lifetime. Tuatara shed their skin at least once per year as adults, Skull Unlike the vast majority of lizards, the tuatara has a complete lower temporal bar closing the lower temporal fenestra (an opening of the skull behind the eye socket), caused by the fusion of the quadrate/quadratojugal (which are fused into a single element in adult tuatara) and the jugal bones of the skull. This is similar to the condition found in primitive diapsid reptiles. However, because more primitive rhynchocephalians have an open lower temporal fenestra with an incomplete temporal bar, this is thought to be a derived characteristic of the tuatara and other members of the clade Sphenodontinae, rather than a primitive trait retained from early diapsids. The complete bar is thought to stabilise the skull during biting. The teeth of the tuatara, and almost all other rhynchocephalians, are described as acrodont, as they are attached to the apex of the jaw bone. This contrast with the pleurodont condition found in the vast majority of lizards, where the teeth are attached to the inward-facing surface of the jaw. The teeth of the tuatara are extensively fused to the jawbone, making the boundary between the tooth and jaw difficult to discern, and the teeth lack roots and are not replaced during the lifetime of the animal, unlike those of pleurodont lizards. It is a common misconception that tuatara lack teeth and instead have sharp projections on the jaw bone; histology shows that they have true teeth with enamel and dentine with pulp cavities. As their teeth wear down, older tuatara have to switch to softer prey, such as earthworms, larvae, and slugs, and eventually have to chew their food between smooth jaw bones. The tuatara possesses palatal dentition (teeth growing from the bones of the roof of the mouth), which is ancestrally present in reptiles (and tetrapods generally). While many of the original palatal teeth present in reptiles have been lost, The structure of the jaw joint allows the lower jaw to slide forwards after it has closed between the two upper rows of teeth. This mechanism allows the jaws to shear through chitin and bone. This proportion has been used by paleontologists trying to estimate the volume of dinosaur brains based on fossils. used for both day and night vision, and a tapetum lucidum which reflects onto the retina to enhance vision in the dark. There is also a third eyelid on each eye, the nictitating membrane. Five visual opsin genes are present, suggesting good colour vision, possibly even at low light levels. Parietal eye (third eye) Like some other living vertebrates, including some lizards, the tuatara has a third eye on the top of its head called the parietal eye (also called a pineal or third eye) formed by the parapineal organ, with an accompanying opening in the skull roof called the pineal or parietal foramen, enclosed by the parietal bones. It has its own lens, a parietal plug which resembles a cornea, retina with rod-like structures, and degenerated nerve connection to the brain. The parietal eye is visible only in hatchlings, which have a translucent patch at the top centre of the skull. After four to six months, it becomes covered with opaque scales and pigment. It likely serves to regulate the circadian rhythm and possibly detect seasonal changes, and help with thermoregulation. Hearing Together with turtles, the tuatara has the most primitive hearing organs among the amniotes. There is no tympanum (eardrum) and no earhole, Odorant receptors Animals that depend on the sense of smell to capture prey, escape from predators or simply interact with the environment they inhabit, usually have many odorant receptors. These receptors are expressed in the dendritic membranes of the neurons for the detection of odours. The tuatara has around 472 receptors, a number more similar to what birds have than to the large number of receptors that turtles and crocodiles may have. The tuatara has gastralia, rib-like bones also called gastric or abdominal ribs, the presumed ancestral trait of diapsids. They are found in some lizards, where they are mostly made of cartilage, as well as crocodiles and the tuatara, and are not attached to the spine or thoracic ribs. The true ribs are small projections, with small, hooked bones, called uncinate processes, found on the rear of each rib. Tail and back The spiny plates on the back and tail of the tuatara resemble those of a crocodile more than a lizard, but the tuatara shares with lizards the ability to break off its tail when caught by a predator, and then regenerate it. The regrowth takes a long time and differs from that of lizards. Well illustrated reports on tail regeneration in tuatara have been published by Alibardi and Meyer-Rochow. The cloacal glands of tuatara have a unique organic compound named tuataric acid. Age determination Currently, there are two means of determining the age of tuatara. Using microscopic inspection, hematoxylinophilic rings can be identified and counted in both the phalanges and the femur. Phalangeal hematoxylinophilic rings can be used for tuatara up to ages 12–14 years, as they cease to form around this age. Femoral rings follow a similar trend, however they are useful for tuatara up to ages 25–35 years. Around that age, femoral rings cease to form. Further research on age determination methods for tuatara is required, as tuatara have lifespans much longer than 35 years (ages up to 60 Tuatara thrive in temperatures much lower than those tolerated by most reptiles, and hibernate during winter. They remain active at temperatures as low as , while temperatures over are generally fatal. The optimal body temperature for the tuatara is from , the lowest of any reptile. The body temperature of tuatara is lower than that of other reptiles, ranging from over a day, whereas most reptiles have body temperatures around . The low body temperature results in a slower metabolism. == Ecology ==

Burrowing seabirds such as petrels, prions, and shearwaters share the tuatara's island habitat during the birds' nesting seasons. The tuatara use the birds' burrows for shelter when available, or dig their own. The seabirds' guano helps to maintain invertebrate populations on which tuatara predominantly prey, including beetles, crickets, spiders, wētās, earthworms, and snails. Their diets also consist of frogs, lizards, and bird's eggs and chicks. In total darkness no feeding attempt was observed, and the lowest light intensity at which an attempt to snatch a beetle was observed occurred under 0.0125 lux. The eggs and young of seabirds that are seasonally available as food for tuatara may provide beneficial fatty acids. Tuatara will bite when approached, and will not let go easily. Female tuatara sometimes exhibit parental behaviour by guarding nests from other females. Tuatara are parasitised by the tuatara tick (Archaeocroton sphenodonti), a tick that directly depends on tuatara. These ticks tend to be more prevalent on larger males, as they have larger home ranges than smaller and female tuatara and interact with other tuatara more in territorial displays. ==Reproduction==

Tuatara reproduce very slowly, taking 10 to 20 years to reach sexual maturity. Though their reproduction rate is slow, tuatara have the fastest swimming sperm by two to four times compared to all reptiles studied earlier. Mating occurs in midsummer; females mate and lay eggs once every four years. During courtship, a male makes his skin darker, raises his crests, and parades toward the female. He slowly walks in circles around the female with stiffened legs. The female will either allow the male to mount her, or retreat to her burrow. Adult males do not have a penis or any form of intromittent phallus. They reproduce by the male lifting the tail of the female and placing his vent (cloaca) over hers. This process is sometimes referred to as a "cloacal kiss". The sperm is then transferred into the female, much like the mating process in birds. Along with birds, the tuatara is one of the few members of Amniota to have lost the ancestral penis. Tuatara eggs have a soft, parchment-like 0.2mm thick shell that consists of calcite crystals embedded in a matrix of fibrous layers. It takes the females between one and three years to provide eggs with yolk, and up to seven months to form the shell. It then takes between 12 and 15 months from copulation to hatching. This means reproduction occurs at two- to five-year intervals, the slowest in any reptile. Survival of embryos has also been linked to having more success in moist conditions. Wild tuatara are known to be still reproducing at about 60 years of age; "Henry", a male tuatara at Southland Museum in Invercargill, New Zealand, became a father (possibly for the first time) on 23 January 2009, at age 111, with an 80-year-old female. Tuatara probably have the slowest growth rates of any reptile, This may be related to genes that offer protection against reactive oxygen species. The tuatara genome has 26 genes that encode selenoproteins and 4 selenocysteine-specific tRNA genes. In humans, selenoproteins have a function of antioxidation, redox regulation and synthesis of thyroid hormones. It is not fully demonstrated, but these genes may be related to the longevity of this animal or may have emerged as a result of the low levels of selenium and other trace elements in the New Zealand terrestrial systems. == Genomic characteristics ==

The most abundant LINE element in the tuatara is L2 (10%). Most of them are interspersed and can remain active. The longest L2 element found is 4 kb long and 83% of the sequences had ORF2p completely intact. The CR1 element is the second most repeated (4%). Phylogenetic analysis shows that these sequences are very different from those found in other nearby species such as lizards. Finally, less than 1% are elements belonging to L1, a low percentage since these elements tend to predominate in placental mammals. In the tuatara, 56 MHC genes have been identified; some of which are similar to MHCs of amphibians and mammals. Most MHCs that were annotated in the tuatara genome are highly conserved, however there is large genomic rearrangement observed in distant lepidosaur lineages. Around 7,500 LTRs have been identified, including 450 endogenous retroviruses (ERVs). Studies in other Sauropsida have recognised a similar number but nevertheless, in the genome of the tuatara it has been found a very old clade of retrovirus known as Spumavirus. ==Conservation==

Tuatara are absolutely protected under New Zealand's Wildlife Act 1953. The species is also listed under Appendix I of the Convention on International Trade in Endangered Species (CITES) meaning commercial international trade in wild sourced specimens is prohibited and all other international trade (including in parts and derivatives) is regulated by the CITES permit system. mainland, in November 2024 Distribution and threats Tuatara were once widespread on New Zealand's main North and South Islands, where subfossil remains have been found in sand dunes, caves, and Māori middens. Wiped out from the main islands before European settlement, they were long confined to 32 offshore islands free of mammals. and are colonised by few animal species, indicating that some animals absent from these islands may have caused tuatara to disappear from the mainland. However, kiore (Polynesian rats) had recently become established on several of the islands, and tuatara were persisting, but not breeding, on these islands. Additionally, tuatara were much rarer on the rat-inhabited islands. The recent discovery of a tuatara hatchling on the mainland indicates that attempts to re-establish a breeding population on the New Zealand mainland have had some success. The total population of tuatara is estimated to be between 60,000 Climate change Tuatara have temperature-dependent sex determination meaning that the temperature of the egg determines the sex of the animal. For tuatara, lower egg incubation temperatures lead to females while higher temperatures lead to males. Since global temperatures are increasing, climate change may be skewing the male to female ratio of tuatara. Current solutions to this potential future threat are the selective removal of adults and the incubation of eggs. Eradication of rats Tuatara were removed from Stanley, Red Mercury and Cuvier Islands in 1990 and 1991, and maintained in captivity to allow Polynesian rats to be eradicated on those islands. All three populations bred in captivity, and after successful eradication of the rats, all individuals, including the new juveniles, were returned to their islands of origin. In the 1991–92 season, Little Barrier Island was found to hold only eight tuatara, which were taken into in situ captivity, where females produced 42 eggs, which were incubated at Victoria University. The resulting offspring were subsequently held in an enclosure on the island, then released into the wild in 2006 after rats were eradicated there. In the Hen and Chicken Islands, Polynesian rats were eradicated on Whatupuke in 1993, Lady Alice Island in 1994, and Coppermine Island in 1997. Following this program, juveniles have once again been seen on the latter three islands. In contrast, rats persist on Hen Island of the same group, and no juvenile tuatara have been seen there as of 2001. In the Alderman Islands, Middle Chain Island holds no tuatara, but it is considered possible for rats to swim between Middle Chain and other islands that do hold tuatara, and the rats were eradicated in 1992 to prevent this. There is another out of country population of Brothers Island tuatara that was given to the San Diego Zoological Society and is housed off-display at the San Diego Zoo facility in Balboa. No successful reproductive efforts have been reported yet. Northern tuatara are given coloured markings on the head for identification. S. punctatus punctatus naturally occurs on 29 islands, and its population is estimated to be over 60,000 individuals. A mainland release of S. p. punctatus occurred in 2005 in the heavily fenced and monitored Karori Sanctuary. In early 2009, the first recorded wild-born offspring were observed. Captive breeding The first successful breeding of tuatara in captivity is believed to have achieved by Sir Algernon Thomas at either his University offices or residence in Symonds Street in the late 1880s or his new home, Trewithiel, in Mount Eden in the early 1890s. Several tuatara breeding programmes are active in New Zealand. Southland Museum and Art Gallery in Invercargill was the first institution to have a tuatara breeding programme; starting in 1986 they bred S. punctatus and have focused on S. guntheri more recently. Hamilton Zoo, Auckland Zoo and Wellington Zoo also breed tuatara for release into the wild. At Auckland Zoo in the 1990s it was discovered that tuatara have temperature-dependent sex determination. The Victoria University of Wellington maintains a research programme into the captive breeding of tuatara, and the Pūkaha / Mount Bruce National Wildlife Centre keeps a pair and a juvenile. The WildNZ Trust has a tuatara breeding enclosure at Ruawai. One notable captive breeding success story took place in January 2009, when all 11 eggs belonging to 110-year-old tuatara Henry and 80-year-old tuatara Mildred hatched. This story is especially remarkable as Henry required surgery to remove a cancerous tumour in order to successfully breed. ==Cultural significance==

Tuatara feature in a number of indigenous legends, and are held as ariki (God forms). Tuatara are regarded as the messengers 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. The tuatara was featured on one side of the New Zealand five-cent coin, which was phased out in October 2006. Tuatara was also the name of the Journal of the Biological Society of Victoria University College and subsequently Victoria University of Wellington, published from 1947 until 1993. It has now been digitised by the New Zealand Electronic Text Centre, also at Victoria. ,1937 ==Notes==