New Zealand’s endemic tuatara is a very unusual animal. They are the only living representative of a group of reptiles known as Rhynchocephalia (sometimes known in the past as Sphenodontia) that first appeared over 200 million years ago. They are not lizards!
The ancestors of tuatara were present on the landmass that would later become New Zealand, when it separated from Gondwana over 80 million years ago. They have evolved in isolation ever since.
As a result, tuatara are commonly referred to as ‘living fossils’. However, this term is inaccurate and misleading. ‘Living fossil’ gives people the idea that tuatara have not changed for millions of years, but this is not the case! Although they are the last representatives of an ancient group of reptile, they are not identical to the fossils of their ancestors and relatives that lived millions of years ago.
Early scientists classified the tuatara as a type of lizard. However, in 1867, Dr Günther at the British Museum took a closer look at a tuatara skeleton and proposed a new order for the tuatara based on a number of distinctive features:
- Skull: Tuatara have a single row of teeth on their lower jaw and a double row on their upper jaw. The upper jaw is attached to the skull in a rigid and inflexible way. This arrangement is unique to the tuatara and affects the way they feed.
- Juvenile tuatara have a horny (not calcified) egg-tooth on their jaw to help them break out of their shell. This falls off shortly after they hatch.
- Skeleton: The vertebrae found in a tuatara spine resemble those in fish and some amphibians, rather than lizards. Their ribs have bony processes more typical of crocodiles than lizards.
- Male tuatara do not have a penis, whereas male lizards have 2.
Habitat and distribution
Tuatara typically live alone in burrows, although they sometimes share these with seabirds. They are most active at night and may spend their days basking outside their burrows. They eat almost everything including insects, snails, frogs, skinks and birds’ eggs (including the eggs of the seabirds with which they share a home!).
Fossil evidence suggests that tuatara were once widespread in New Zealand. Remains of their distinctive jawbones have been found in sand dunes, peat bogs, caves and Māori middens. Tuatara are now restricted to a number of mainland and offshore islands.
Threats to survival
Like our other native reptiles and amphibians, the major threat to the survival of tuatara is introduced mammalian predators. Rats are a particular threat, and the majority of our remaining tuatara now only survive and breed on mainland and offshore islands that are rat-free.
Tuatara are also threatened by humans that capture them to sell overseas. This smuggling is illegal, but tuatara are highly sought after by reptile collectors and may fetch very high prices overseas. In the past, tuatara have been stolen from zoos and offshore islands.
Saving the tuatara
Staff members of the Department of Conservation administer the Tuatara Recovery Plan. They collaborate with universities, zoos and other government agencies to protect the remaining populations of tuatara.
Scientists have debated how many species of tuatara should be recognised. In 1990, information from DNA analysis suggested that the population on North Brother Island in Cook Strait should be recognised as a separate species to the common tuatara (Sphenodon punctatus). However, based on the most recent DNA analyses, from 2009, scientists have recognised only one species.
Nature of science
Scientists sometimes reclassify organisms in the light of new information that shows that their relationship to other organisms is different to what was previously thought.
The tuatara is currently ranked as ’at risk’ (not endangered or threatened). However, scientists are concerned about the long-term stability of tuatara populations as they are often restricted to small islands and are particularly vulnerable to climate change and the introduction of rats and other predators.
There are 4 main conservation strategies for tuatara:
- Mammal eradications from offshore islands.
- Egg incubation programmes – where eggs are collected from the wild and incubated in controlled laboratory environments.
- Head start programmes – where young tuatara, hatched in the laboratory, are kept in special enclosures before they are released onto offshore islands when they reach maturity.
- Translocation – when a number of tuatara are transported to a new area to establish a new population or to help restore an existing population.
Conservation ranking in action explores the processes and criteria used to rank animals according to their conservation threat status.
Find out more about tuatara on the Department of Conservation (DOC) website, including more details about DOC’s historic Tuatara Recovery Plan.
The genome sequence of the tuatara sheds light on the species’ evolution and on conservation strategies, read about this new work in this 2020 article from Nature.
Watch rare footage of a tuatara hatching in this video from Victoria University of Wellington.
Listen to Dr Nelson in this podcast talking about warmer temperatures resulting in an accelerating decline in the proportion of adult female tuatara (scroll down the page for 'Tuatara and climate change'). Understanding mechanisms underlying population declines is critical in preventing the extinction of endangered populations.
Read this research from 2022 about how a newly discovered Arizona fossil suggests tuatara are 190 million years old and it's skeleton has hardly changed since.
In this The Conversation article discover that though Tuatara are returning to the mainland – feeding the hungry reptiles could be more difficult than expected.