Endangered Reptiles From the Age of the Dinosaurs
Tuatara are endemic to New Zealand, quite unlike other reptiles, and have become endangered through mammal predation.
Tuatara are New Zealand’s living dinosaurs, with many unusual features that set them apart from other reptiles. Their slow growth and breeding cycle made them vulnerable to predation when humans arrived in New Zealand, meaning they have to be actively conserved to ensure their continued survival.
Tuatara History and Distinctive Features
Tuatara look like lizards but are the only surviving member of a much older order, the Rhynchocephalia that evolved with the dinosaurs around 225 million years ago. All other Rhynchocephalians died out with the dinosaurs 65 million years ago. Tuatara, isolated on what was to become New Zealand, survived the mass extinction and are now referred to as ‘living fossils’.
The scientific name is Sphenodon punctatus. Until recently, two species of tuatara were recognized. However, DNA analysis has shown they are one species with geographic variations.
They have distinctive features that separate them from modern lizards. They have a single row of teeth in their lower jaw, which are bony extensions of their jaws. They have two rows of teeth in their upper jaw, which the bottom row fits between. As these are not true teeth, they are not replaced when worn or damaged. Very old tuatara merely grind food between their jawbones.
Baby tuatara have a ‘third eye’ in the middle of their foreheads. It is not a proper eye, like their two main eyes, but is extremely sensitive to light. It may be used to influence the amount of time the animal spends basking in the sun or may be a means for young tuatara to escape predation by adults, allowing them to feed at dawn and dusk when adult tuatara are in their burrows.
Other features that distinguish tuatara from other reptiles are their ability to hold their breath for up to an hour, and the fact that male tuatara do not have a penis and mate like birds using a cloaca. They have a very slow rate of growth in and outside the egg, and embryos stop developing during winter, which is highly unusual.
Tuatara Lifecycle and Biology
Tuatara mate between January and March. Eggs that look like ping-pong balls develop inside the female, who eventually lays them in earth nests between October and December. The eggs stay in the ground, with the adults playing no part in their care, for a further 11 to 16 months. Hatchlings finally appear about 2 years after they were conceived.
Hatchlings are small and well camouflaged. Their sex depends on the temperature of the soil surrounding the eggs. Below 21 degrees C, hatchlings will be female, at 22 degrees C or more they will be male. At 21 degrees C there is an equal chance of being each sex.
Tuatara grow very slowly, not reaching sexual maturity for at least ten years and reaching their full adult size when they are about 35. Their growth and sexual maturity depend on temperature, so tuatara in northern New Zealand mature faster than those further south.
They are solitary as adults, maintaining a territory and spending much of their time in an underground burrow. Being cold-blooded, they bask outside on warm, sunny days to absorb energy to hunt at night. They feed on large invertebrates, such as weta (bush crickets), worms, spiders and lizards. On offshore islands, they eat the eggs and chicks of seabirds. They have also been observed eating small mammals, such as mice, so turning the tables on their predators.
Tuatara were abundant all over New Zealand before humans colonized. But they were close to extinction on the mainland even before Europeans arrived due to predation by the kiore, or Polynesian rat, brought by Maori.
The species became fully protected by law in 1895, one of the world’s first. Remnant populations hung on in 32 remote islands where no mammal pests existed. The largest population of 50,000 survives on Stephens Island in the Marlborough Sounds with smaller populations in the Sounds, and near Auckland, Northland and the Coromandel Peninsula.
Tuatara have been reintroduced in conservation efforts at other sites, such as Matiu/Somes Island in Wellington Harbour and at Zealandia: Karori Sanctuary, the only mainland site that supports wild tuatara inside a predator-proof fence.
Tuatara are a priority for conservation in New Zealand. Breeding programs, research and pest eradication on islands will ensure their long-term survival.