Taxonomy & Related Groups comparison

Tuatara vs Iguana: Key Differences Explained

The short answer

The tuatara looks like a lizard but is not one. It is the only surviving member of Rhynchocephalia, an order that separated from lizards and snakes far back in reptile history, and it survives only in New Zealand. Iguanas are squamates, true lizards in the family Iguanidae, native to the Americas and some Pacific islands. The tuatara has no external ear openings and two upper tooth rows; iguanas have both an ear opening and replaceable teeth.

The main difference

The tuatara is the last survivor of an order outside Squamata, while the iguana is an ordinary squamate lizard, despite the two looking broadly alike.

The tuatara is filed as a lizard almost everywhere outside specialist sources, and setting it beside a large, familiar, genuinely lizard-shaped iguana is the clearest way to show what the difference in lineage actually consists of.

At a glance

Comparison of Tuatara and Iguana across 7 dimensions, with an interpretation of each difference.
What differs	Tuatara	Iguana	What it means
Lineage	The sole surviving genus of the order Rhynchocephalia, outside Squamata entirely	A squamate lizard in the family Iguanidae, alongside snakes and other lizards in Squamata	The two are separated at ordinal level, which is a far deeper split than the shared body plan suggests.
External ear	No external ear opening and no visible eardrum	A conspicuous external ear opening with a visible tympanum behind the jaw	This is the easiest structural check anyone can make on a photograph of the head.
Teeth	Two rows of upper teeth that the single lower row fits between, fused to the jaw bone and not replaced	A single row on each jaw, attached to the inner side of the bone and replaced through life	Tooth arrangement is the classic diagnostic and explains why old tuatara wear their teeth flat.
Preferred temperature	Active at unusually low body temperatures, often in the region of about 7 to 20 degrees Celsius	Prefers warm conditions and basks to reach considerably higher working temperatures	Cold tolerance lets the tuatara occupy windswept temperate islands where most reptiles cannot.
Range	Restricted to New Zealand, chiefly offshore islands plus managed mainland sanctuaries	Central and South America and the Caribbean, with related genera in Fiji and Tonga	Their ranges are on opposite sides of the Pacific and have never overlapped naturally.
Adult diet	Invertebrates such as beetles and wetas, plus lizards, seabird eggs and chicks	Largely leaves, flowers and fruit in adults of the green iguana, fermented in an enlarged hindgut	One is a cool-climate carnivore, the other a tropical herbivore, despite similar silhouettes.Juvenile iguanas take more invertebrate matter than adults, and diets differ between iguanid genera.
Activity pattern	Mainly nocturnal as adults, sheltering in burrows often shared with breeding seabirds	Diurnal, basking openly in trees or on rocks and retreating to cover at night	Night activity at low temperatures is a genuine physiological difference, not just a habit.

Lineage: TuataraThe sole surviving genus of the order Rhynchocephalia, outside Squamata entirely
IguanaA squamate lizard in the family Iguanidae, alongside snakes and other lizards in Squamata
The two are separated at ordinal level, which is a far deeper split than the shared body plan suggests.
External ear: TuataraNo external ear opening and no visible eardrum
IguanaA conspicuous external ear opening with a visible tympanum behind the jaw
This is the easiest structural check anyone can make on a photograph of the head.
Teeth: TuataraTwo rows of upper teeth that the single lower row fits between, fused to the jaw bone and not replaced
IguanaA single row on each jaw, attached to the inner side of the bone and replaced through life
Tooth arrangement is the classic diagnostic and explains why old tuatara wear their teeth flat.
Preferred temperature: TuataraActive at unusually low body temperatures, often in the region of about 7 to 20 degrees Celsius
IguanaPrefers warm conditions and basks to reach considerably higher working temperatures
Cold tolerance lets the tuatara occupy windswept temperate islands where most reptiles cannot.
Range: TuataraRestricted to New Zealand, chiefly offshore islands plus managed mainland sanctuaries
IguanaCentral and South America and the Caribbean, with related genera in Fiji and Tonga
Their ranges are on opposite sides of the Pacific and have never overlapped naturally.
Adult diet: TuataraInvertebrates such as beetles and wetas, plus lizards, seabird eggs and chicks
IguanaLargely leaves, flowers and fruit in adults of the green iguana, fermented in an enlarged hindgut
One is a cool-climate carnivore, the other a tropical herbivore, despite similar silhouettes.Juvenile iguanas take more invertebrate matter than adults, and diets differ between iguanid genera.
Activity pattern: TuataraMainly nocturnal as adults, sheltering in burrows often shared with breeding seabirds
IguanaDiurnal, basking openly in trees or on rocks and retreating to cover at night
Night activity at low temperatures is a genuine physiological difference, not just a habit.

How they are related

Rhynchocephalia and Squamata diverged deep in reptile history, and the tuatara is the only rhynchocephalian left, while Squamata contains lizards, snakes and amphisbaenians. Iguanidae sits within that squamate radiation, and the iguana label is applied both narrowly to the genus Iguana and loosely to a much wider set of related lizards. Calling a tuatara a lizard is therefore not a minor imprecision but a placement in the wrong order.

A note on naming: Tuatara refers to the single surviving genus Sphenodon, whose species-level taxonomy has been debated, while iguana is used both for the genus Iguana and loosely for a much broader set of iguanid lizards.

Telling them apart

Check the side of the head first: an iguana has a clear ear opening with a visible eardrum, and a tuatara has none. Then look at the crest. A tuatara's spiny dorsal crest is made of soft, folded skin projections, most prominent in males, while a green iguana's crest is a row of firm pointed scales running from neck to tail. Iguanas also have a large throat dewlap that tuatara lack.

No visible ear opening, soft-spined crest, cool windy island in New Zealand, active at night: tuatara, and not a lizard. Visible ear opening with a large round scale below it, firm spiny crest, big throat dewlap, basking in a tropical tree: iguana, and a true lizard. The two are not close relatives at any level below Reptilia.

Habitat and distribution

The tuatara lives on cool, windy New Zealand islands with seabird colonies, sheltering in burrows in soil bound by coastal vegetation, and has been reintroduced to fenced mainland sanctuaries. Green iguanas live in tropical lowland forest, riverbank and increasingly urban vegetation in the Americas, and are strong swimmers that drop from overhanging branches into water. Other iguanid genera occupy arid rock, scrub and remote Pacific islands.

Diet and ecological role

The tuatara is a slow, opportunistic carnivore taking beetles, wetas, spiders, small lizards and, where it shares burrows with seabirds, eggs and chicks. Green iguanas are among the most committed herbivorous lizards, processing leaves, flowers and fruit through an enlarged hindgut with a microbial community that ferments plant fibre. The two therefore occupy quite different positions in their food webs despite similar body proportions.

Behaviour

Tuatara are extremely slow-living: growth continues for decades, and females in cool conditions may reproduce only at multi-year intervals. Sex is determined by incubation temperature, which makes the species a focus of concern under warming. Iguanas grow rapidly by comparison, defend basking territories with head-bobbing displays and dewlap extension, and rely on speed, swimming and the tail when threatened.

Senses and adaptations

Hatchling tuatara show a well-developed parietal eye on top of the head, a light-sensitive structure with a lens and retina that becomes covered by scales and pigment as the animal grows. Many lizards, iguanas included, also have a parietal organ, so its presence is not unique to tuatara, only unusually well developed. The tuatara's low-temperature metabolism supports activity on nights that would immobilise most lizards.

More on this topic: Animal senses and adaptations.

Lifespan and life stages

Tuatara are exceptionally long-lived: individuals are known to have passed fifty years, growth continues for several decades, and lifespans beyond a century have been proposed, though such figures rest on indirect estimation rather than continuous records. Green iguanas mature within a few years and reported captive lifespans reach into the teens and twenties, with wild survival typically far shorter given predation and, in introduced ranges, control programmes.

People and these animals

Tuatara are strictly protected in New Zealand, hold deep significance in Maori tradition, and their recovery has depended on removing introduced rats from islands. They are not kept as pets. Green iguanas are traded internationally in very large numbers, are farmed and eaten in parts of their range, and have established damaging introduced populations in places such as Florida, where they affect infrastructure and native vegetation.

Keeping them: what to understand first

Green iguanas are among the most commonly traded reptiles and among the most commonly surrendered, because hatchlings are small while adults are large, long-lived and demanding. Tuatara are protected and are not pet animals under any circumstances. Whether any reptile suits a home depends on local law, household circumstances, welfare capacity and long-term responsibility, and care questions belong with a qualified reptile veterinarian.

Conservation context

Tuatara populations collapsed on the New Zealand mainland after introduced mammals arrived, and survival has depended on predator-free islands and fenced sanctuaries, with translocations continuing and rat eradication underpinning most of the successful sites. Temperature-dependent sex determination adds a further concern under a warming climate. Iguanid species range from abundant and invasive outside their native range to critically restricted island endemics, so the label covers extremes. Assessments are revised as new survey data arrives.

Tuatara conservation depends on ongoing island management, and iguanid statuses range from invasive to critically restricted. Consult the current IUCN Red List entry for the specific species rather than a group-level statement.

What they have in common

Both are reptiles with a broadly lizard-like body plan, four limbs and a long tail.
Both have a dorsal crest that is more developed in males and used in display.
Both possess a parietal organ on top of the head, though it is far more developed in the tuatara.
Both are egg-layers whose incubation conditions influence how the young develop.

Key differences

The tuatara is the last rhynchocephalian; the iguana is a squamate lizard.
Tuatara have no external ear opening, while iguanas show a clear eardrum behind the jaw.
Tuatara have two upper tooth rows fused to the jaw; iguanas replace single-row teeth for life.
Tuatara are cool-climate nocturnal carnivores; green iguanas are tropical diurnal herbivores.
Tuatara occur only in New Zealand, while iguanas are American with Pacific island relatives.

Where people go wrong

Filing the tuatara as a lizard when it belongs to a separate reptile order.
Reading the tuatara's third eye as unique, when many lizards including iguanas have a parietal organ.
Assuming a spiny crest means the two are related, when the structures differ in makeup.
Treating iguana as one species when the name spans a genus and, loosely, a much wider family.

Frequently asked questions

Why is the tuatara not classified as a lizard?

Because it belongs to a different order. Lizards are squamates, and the tuatara is the last survivor of Rhynchocephalia, a lineage that split from the squamate line very early in reptile evolution. The resemblance is a matter of a conserved body plan rather than close kinship. Skull structure, tooth attachment, the absence of an ear opening and several skeletal features all place it outside Squamata.

How do tuatara teeth differ from an iguana's?

A tuatara has two rows of teeth in the upper jaw with a single lower row that closes between them, and the teeth are fused to the jaw bone rather than set in sockets, so they are not replaced. Very old animals wear them almost flat and rely on the jaw edges. An iguana has one row per jaw, attached to the inner bone surface, and replaces teeth throughout life.

Do both tuatara and iguanas have a third eye?

Both have a parietal organ, so the tuatara's is not unique, only unusually well developed. In hatchling tuatara it is visible on top of the head with a lens and retina before scales and pigment cover it. Iguanas and many other lizards have a parietal spot that helps regulate daily and seasonal rhythms and detect overhead shadow. The tuatara's version is simply the most elaborate among living reptiles.

Where can tuatara be seen, and do they overlap with iguanas anywhere?

Nowhere in the wild do they overlap. Tuatara occur only in New Zealand, chiefly on predator-free offshore islands and in a small number of fenced mainland sanctuaries and managed enclosures. Iguanas are American animals, with related genera on Fiji and Tonga, and introduced populations in places such as Florida. The Pacific separates the two ranges, and no natural contact has ever existed.

Why can tuatara stay active at temperatures that would slow an iguana down?

The tuatara evolved in a cool temperate climate and functions at body temperatures often in the region of about seven to twenty degrees Celsius, far below what most reptiles need. Its metabolism runs slowly, which suits low-energy nocturnal foraging on windy islands. Iguanas evolved in the tropics, bask to reach much higher working temperatures, and become sluggish when cold, which is why cold snaps in Florida immobilise introduced individuals.

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Sources and methodology

How this comparison is built: FaunaHub comparisons are assembled from the sourced animal profiles behind them rather than written as standalone claims. Figures such as size, mass, and lifespan are typical ranges that vary by subspecies, population, region, sex, age, and — where relevant — whether an animal lives in the wild or under human care, so they are presented as ranges rather than fixed values. Where a common name covers a group rather than a single species, the page says so instead of implying a species-to-species match. Conservation status changes over time and should be confirmed against the current IUCN Red List. Dimensions that could not be supported from the underlying profiles are omitted rather than filled in.

What this page does not do: it does not rank the two animals, predict the outcome of a confrontation, or present either one as stronger, smarter, or better. It is not veterinary, medical, first-aid, handling, capture, hunting, or pest-control guidance. For an animal in your care, or any situation involving injury, contact a qualified veterinarian, your local wildlife authority, or emergency services.

Sources and further reading

Authoritative references used for general educational context. External links open in a new tab. These sources do not endorse FaunaHub.

UniversityAnimal Diversity Web — Sphenodon punctatus (tuatara) — University of Michigan species account
ReferenceBritannica — Tuatara — Editor-reviewed encyclopedia entry
Wildlife referenceIUCN Red List of Threatened Species — Authoritative source for current conservation status
UniversityAnimal Diversity Web — Iguana iguana (green iguana) — University of Michigan species account
ReferenceEncyclopaedia Britannica — Animals reference — Editor-reviewed encyclopedia overview entries
ReferenceThe Reptile Database — Museum-backed taxonomic database of reptile species
UniversityAnimal Diversity Web — University of Michigan Museum of Zoology — Peer-edited reference accounts for animal species

Last updated: 2026-08-04