Tuatara (Sphenodon punctatus)

Also known as: beak-head, Brothers Island tuatara, common tuatara, Cook Strait tuatara, Gunther’s tuatara, Günther’s tuatara, sphenodon
Synonyms: Hatteria punctata, Sphenodon guntheri, Sphenodon punctatum
  
French: Hatteria Ponctué, Sphénodon Ponctué
Spanish: Tuátara
KingdomAnimalia
PhylumChordata
ClassReptilia
OrderRhynchocephalia
FamilySphenodontidae
GenusSphenodon (1)
SizeMale total length: up to 61 cm (2)
Female total length: up to 45 cm (2)
Snout-vent length: up to 28 cm (3)
Male weight: up to 1 kg (4)
Female weight: up to 0.5 kg (4)
Top facts

The tuatara is classified as Least Concern (LC) on the IUCN Red List (1) and is listed on Appendix I of CITES (5). The Brothers Island tuatara (Sphenodon guntheri or possible subspecies Sphenodon punctatus guntheri) is classified as Vulnerable (VU) on the IUCN Red List (1).

An unusual and unique reptile found only in New Zealand, the tuatara (Sphenodon punctatus) has been dubbed a ‘living fossil’ as it is the only surviving member of an ancient group of reptiles that flourished during the time of the dinosaurs (2) (6) (7) (8) (9). The name of this group, Rhynchocephalia, means ‘beak heads’, referring to the overhanging upper jaw of these species (2) (3).

The tuatara is a medium-sized reptile and superficially resembles a lizard in appearance. It has a large head, a stout body, powerful limbs with sharp claws, and a thick tail (3) (8), but it differs from lizards in details of its internal anatomy (8) (9). Unlike lizards, the tuatara also has unusual dentition, with a single row of teeth in the lower jaw which fits into a groove between two rows of teeth in the upper jaw (2) (9). The teeth of this species are not set in sockets, instead being simple serrations in the jaw bone (2) (7). The tuatara has no external ear opening, although it is still able to hear (7) (8).

The body of the tuatara varies from olive-green to grey, blackish-brown or pinkish, and is often marked with pale speckles (2) (8) which give this reptile its scientific name punctatus, meaning ‘speckled’ or ‘spotted’ (10). The speckles tend to be brighter in juveniles and in adults which have recently shed their skin (8). Newly hatched tuatara are brownish-pink or grey, sometimes with light patches on the body and tail (2) (8).

The name ‘tuatara’ comes from New Zealand Maori words meaning ‘peaks on the back’, referring to the conspicuous folds of skin and spiny crest along this species’ neck, back and tail (2) (8) (10) (11). The spines are usually white (12) and are most prominent in males, being raised during territorial or courtship displays (2) (7) (10). The adult male tuatara can also be distinguished from the adult female by its larger size (4) (8) (10), more triangular head (4) (10) and less pear-shaped abdomen (10).

A further unusual feature of the tuatara is that it possesses a ‘third eye’, also known as a parietal or pineal eye, which is located centrally on top of the head, beneath the skin (2) (7) (8). This ‘eye’ has a lens and retina, but its exact function is unclear (8). It is sensitive to light but is not thought to form images, instead potentially being involved in regulating the tuatara’s exposure to the sun (2). Although the parietal eye is not unique to the tuatara, it is better developed in this species than in any other animal (8).

The tuatara has been reported to sometimes produce a harsh croaking sound, similar to the call of a frog (8).

Until recently, the tuatara has generally been considered to comprise two separate species, the common tuatara (Sphenodon punctatus) and the Brothers Island tuatara (Sphenodon guntheri) (1) (6) (8) (9) (13), with the Brothers Island tuatara being slightly smaller (14). The common tuatara has also sometimes been further divided into two subspecies (6) (9) (13). However, the taxonomy of the tuatara is debated and more recently some scientists have considered it to be a single species, albeit with distinctive and important geographical variations (6) (15).

The tuatara is endemic to New Zealand. It once occurred throughout the mainland, but after the arrival of humans and other mammals, it survived on just over 30 offshore islands in Cook Strait and off the north-eastern part of the North Island (2) (6) (8) (9) (11).

The Brothers Island tuatara (formerly the species S. guntheri) occurs naturally only on North Brother Island, a four-hectare island in Cook Strait, although translocated populations have now been established on three other islands (2) (12) (16). Other tuatara populations have also been translocated and reintroduced to further islands (2) (6), and several populations have now been reintroduced into sanctuaries on New Zealand’s North and South Islands, marking the return of the species to the mainland (12) (17).

On the offshore islands on which it survives, the tuatara typically inhabits coastal forest or low scrub (2) (4) (9), generally preferring relatively open areas with little ground cover and with crumbly soil in which it can burrow (4) (9).

The islands on which the tuatara lives usually support colonies of breeding seabirds (6) (8), whose burrows and droppings help to enhance soil fertility and encourage a greater abundance of the tuatara’s invertebrate prey (2) (4) (6) (9) (10).

The tuatara has a low metabolic rate and is well adapted to being active at cool temperatures (2) (8), which vary seasonally from 5 to 28 degrees Celsius (4) (9). This reptile does not need standing water in its habitat, but does make the most of rainfalls during otherwise dry summer months (4) (9) (12).

The tuatara lives in burrows, either digging one itself or sharing the burrow of a nesting seabird (2) (4) (8). A nocturnal species, the tuatara emerges from its burrow at night to feed, but it may also come out to bask in the sun during the day (2) (3) (8) (9). This reptile has relatively few natural predators, although it may potentially be taken by birds of prey, kingfishers and gulls (9). If attacked, the tuatara is able to shed its tail and then grow a new one (8) (10).

A ‘sit and wait’ predator, the tuatara generally waits for prey to approach (4) (18), and it hunts mainly by sight (2). Its diet includes a variety of small animals, particularly invertebrates such as beetles, crickets and other large insects. It also eats spiders, snails, worms and small lizards, and will even take the eggs and chicks of seabirds (2) (4) (8) (9) (18), as well as occasional adult birds and some carrion (8) (18).

Most prey is seized in the tuatara’s mouth and crushed between its jaws. Small prey may be eaten whole, but larger animals may be killed by persistent biting and then gnawed (18). The tuatara has a unique jaw motion which gives its teeth a shearing, sawing action, allowing it to process food more efficiently (2) (9) (19).

The tuatara mates in the summer, between January and March (2) (4) (9). At this time, males become territorial and will attempt to warn off intruders by inflating their bodies and raising their crests. Aggressive encounters may also involve head shaking, opening and closing the mouth, and sometimes chasing and biting (3) (4) (7). When courting a female, the male tuatara erects its crest and circles the female in a slow, exaggerated, stiff-legged walk (3) (4) (10).

The female tuatara does not lay her eggs until the spring, from October to December (2) (3) (4) (8) (9). At this time, the female chooses a suitable nesting site, typically in an open, sunny area on a warm, north-facing slope, and digs a shallow hole (4) (9). Up to 18 or 19 oval, soft-shelled eggs are laid, and the female then back-fills the hole and may cover it with leaves and grass (4) (8). The female tuatara may guard the nest for a few days to prevent other females digging it up (4) (20), but the eggs are then abandoned (2) (8) (9).

The tuatara’s eggs hatch after 11 to 16 months (3) (9), one of the longest incubation periods known for any reptile (2) (8). The newly hatched tuatara are active by day for the first two months of life, only later starting to burrow and becoming nocturnal (2) (9) (10). As in many reptiles, the sex of the tuatara is determined by the temperature at which the eggs are incubated (4) (9), but this species is unusual in that higher temperatures produce males and lower temperatures produce females, rather than the other way around (2) (21) (22).

Tuatara grow slowly and do not reach sexual maturity until they are around 9 to 13 years old (2) (23). Growth may continue for many more years, and the tuatara can potentially live to over 60 years old (7) (23), or possibly even to over 100 (2) (8). As well as developing slowly, the tuatara also reproduces very slowly, and females are thought to lay eggs only once every four years on average (3) (4) (9). Tuatara on North Brother Island breed even more slowly, producing eggs only around once every nine years (24), and laying relatively small clutches of three to eight eggs (24) (25).

The loss of the tuatara from mainland New Zealand is thought to have been caused by habitat destruction and the introduction of mammalian predators, particularly rats (2) (4) (8). Studies on islands where rats and tuatara coexist have shown that tuatara numbers are low, few juveniles are present and adults are in poor condition, suggesting that rats prey on tuatara eggs and young as well as competing with adults for food (9) (26) (27). As it breeds so slowly, the tuatara cannot make up for these losses (6), and the species has become extinct on a number of rat-inhabited islands in the past century (9) (28).

Although work has been done to remove rats from many islands, tuatara populations are still at risk from accidental reintroductions of these non-native mammals (6) (9). Many tuatara populations are small, so low genetic diversity may also be a threat, potentially affecting the species’ ability to adapt to change (6). Illegal capture of tuatara has also sometimes occurred (9), and the small islands this reptile inhabits are at risk from any chance events, such as fires (21).

A further threat to the tuatara may come from climate change. As its sex is temperature-dependent, a warmer climate may produce more males, leading to a skewed sex ratio (21) (22) (24) (25). This is likely to be a particular problem on North Brother Island, where the tuatara population is already biased towards males (22) (24). It remains to be seen whether the species will be able to adapt by changing its nesting behaviour (24) (25).

The overall tuatara population is believed to number around 50,000 to 60,000 individuals (8) (9). However, by the year 2000 the population of the Brothers Island tuatara (formerly the species S. guntheri) had been estimated at only around 473 adults, and most Brothers Island tuatara are confined to just 2.2 hectares of North Brother Island. This population almost became extinct due to the construction of a lighthouse and accompanying buildings on the island in the late 19th century, and although it is now recovering it has low genetic diversity and a particularly low breeding rate (16). Subsequent automation of the lighthouse may pose a further threat, as a lack of lighthouse keepers increases the risk of illegal landings on the island (13).

A range of conservation measures are in place to try and save this rare and unique reptile. The tuatara is legally protected (2) (10) (21), and is also listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), meaning that international trade in this species is prohibited (5). The New Zealand Department of Conservation has put a recovery plan in place to guide conservation efforts for the tuatara (9), and has also produced a plan for the management of the species in captivity (4).

One of the main actions to protect tuatara has been the eradication of rats from many of the islands it inhabits (9). Long-term monitoring programmes have been recommended to assess the effectiveness of these eradications, but may need to continue for several decades to detect the effects on this long-lived reptile (28). Further rat eradication programmes are also planned, and care needs to be taken to ensure rats do not re-invade any islands (9).

Captive incubation of wild eggs is also playing a major role in tuatara conservation. Eggs have been successfully hatched in captivity, and both adult and juvenile tuatara have been translocated to a number of rodent-free islands to establish new populations (6) (9) (25) (29) (30). Captive-raised juveniles have also been released to augment existing populations (9), and in 2012 over 200 tuatara were reintroduced to 4 predator-free mainland sanctuaries and one offshore island (17). In addition, captive tuatara can play an important role in education, public awareness and research (4) (6) (9).

Habitat restoration and management will be important for some tuatara populations (9), particularly on North Brother Island (13) (16). To combat the potential effects of global warming, tuatara may need to be moved to cooler sites (24), and a model has been developed to predict the suitability of different areas (25). One of the mainland sites to which tuatara were moved in 2012 is in the southern part of the South Island, approximately 600 kilometres further south than the most southern naturally occurring population in Cook Strait, and will therefore have a cooler climate (12).

As well as further research into the tuatara’s behaviour and biology (9), more work needs to be done to clarify its taxonomy, as this will have an impact on how its populations are managed and how conservation resources are allocated (9) (13). Fortunately, intensive conservation work in recent decades has given the tuatara a more secure conservation status, giving hope that this distinctive, prehistoric-looking reptile can survive into the future (9).

Find out more about the tuatara and its conservation:

Authenticated (25/07/13) by Susan Keall and Nicola Nelson, Allan Wilson Centre for Molecular Ecology and Evolution, School of Biological Sciences, Victoria University of Wellington.
http://www.victoria.ac.nz/home

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  3. Zug, G.R., Vitt, L.J. and Caldwell, J.P. (2001) Herpetology: An Introductory Biology of Amphibians and Reptiles. Second Edition. Academic Press, San Diego.
  4. Blanchard, B., Wellington Zoo, and the Tuatara Recovery Group, Department of Conservation (2002) Tuatara Captive Management Plan and Husbandry Manual. Department of Conservation, Wellington, New Zealand. Available at:
    http://www.doc.govt.nz/documents/science-and-technical/tsop21.pdf
  5. CITES (May, 2013)
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  15. Hay, J.M., Sarre, S.D., Lambert, D.M., Allendorf, F.W. and Daugherty, C.H. (2010) Genetic diversity and taxonomy: a reassessment of species designation in tuatara (Sphenodon: Reptilia). Conservation Genetics, 11: 1063-1081.
  16. Hoare, J.M., Pledger, S., Keall, S.N., Nelson, N.J., Mitchell, N.J. and Daugherty, C.H. (2006) Conservation implications of a long-term decline in body condition of the Brothers Island tuatara (Sphenodon guntheri). Animal Conservation, 9(4): 456-462.
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  20. Refsnider, J.M., Keall, S.N., Daugherty, C.H. and Nelson, N.J. (2009) Does nest-guarding in female tuatara (Sphenodon punctatus) reduce nest destruction by conspecific females? Journal of Herpetology, 43(2): 294-299.
  21. Nelson, N.J., Keall, S.N., Pledger, S. and Daugherty, C.H. (2002) Male-biased sex ratio in a small tuatara population. Journal of Biogeography, 29: 633-640.
  22. Mitchell, N.J., Nelson N.J., Cree, A., Pledger, S., Keall, S.N. and Daugherty, C.H. (2006) Support for a rare pattern of temperature-dependent sex determination in archaic reptiles: evidence from two species of tuatara (Sphenodon). Frontiers in Zoology, 3: 9.
  23. Castanet, J., Newman, D.G. and Girons, H.S. (1988) Skeletochronological data on the growth, age, and population structure of the tuatara, Sphenodon punctatus, on Stephens and Lady Alice Islands, New Zealand. Herpetologica, 44(1): 25-37.
  24. Mitchell, N.J., Allendorf, F.W., Keall, S.N., Daugherty, C.H. and Nelson, N.J. (2010) Demographic effects of temperature-dependent sex determination: will tuatara survive global warming? Global Change Biology, 16: 60-72.
  25. Mitchell, N.J., Kearney, M.R., Nelson, N.J. and Porter, W.P. (2008) Predicting the fate of a living fossil: how will global warming affect sex determination and hatching phenology in tuatara? Proceedings of the Royal Society B - Biological Sciences, 275: 2185-2193.
  26. Towns, D.R. et al. (2007) Responses of tuatara (Sphenodon punctatus) to removal of introduced Pacific rats from islands. Conservation Biology, 21(4): 1021-1031.
  27. Tyrrell, C.L., Cree, A. and Towns, D.R. (2000) Variation in Reproduction and Condition of Northern Tuatara (Sphenodon punctatus punctatus) in the Presence and Absence of Kiore. Science for Conservation 153, Department of Conservation, Wellington, New Zealand.
  28. Cree, A., Daugherty, C.H. and Hay, J.M. (1995) Reproduction of a rare New Zealand reptile, the tuatara Sphenodon punctatus, on rat-free and rat-inhabited islands. Conservation Biology, 9(2): 373-383.
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