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| Tuatara | |
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| Northern tuatara (Sphenodon punctatus punctatus) | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Rhynchocephalia |
| Family: | Sphenodontidae |
| Genus: | Sphenodon Gray, 1831 (conserved name) |
| Species: | S. punctatus
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| Binomial name | |
| Sphenodon punctatus (Gray, 1842) (conserved name)
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| Native range (New Zealand) | |
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| Current distribution of tuatara (in black):[5][6][7] Circles represent the North Island tuatara, and squares the Brothers Island tuatara. Symbols may represent up to seven islands. | |
| Synonyms | |
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The tuatara (Sphenodon punctatus) is a species of reptile endemic to New Zealand. Despite its close resemblance to lizards, it is part of a distinct lineage, the order Rhynchocephalia.[8] The name tuatara is derived from the Māori language and means "peaks on the back".[9]
The single extant species of tuatara is the only surviving member of its order, which was highly diverse during the Mesozoic era.[10] Rhynchocephalians first appeared in the fossil record during the Triassic, around 240 million years ago,[11] and reached worldwide distribution and peak diversity during the Jurassic, when they represented the worlds dominant group of small reptiles. Rhynchocephalians underwent a great decline during the Cretaceous with their youngest records outside New Zealand dating to the Paleocene. Their closest living relatives are squamates (lizards and snakes). Tuatara are of interest for studying the evolution of reptiles.
Tuatara are greenish brown and grey, and measure up to 80 cm (31 in) from head to tail-tip and weigh up to 1.3 kg (2.9 lb)[12] with a spiny crest along the back, especially pronounced in males. They have two rows of teeth in the upper jaw overlapping one row on the lower jaw, which is unique among living species. They are able to hear, although no external ear is present, and have unique features in their skeleton.
Tuatara are sometimes referred to as "living fossils",[8] which has generated significant scientific debate. This term is currently deprecated among paleontologists and evolutionary biologists. Although tuatara have preserved the morphological characteristics of their Mesozoic ancestors (240–230 million years ago), there is no evidence of a continuous fossil record to support this.[13][10] The species has between 5 and 6 billion base pairs of DNA sequence, nearly twice that of humans.[14]
The tuatara (Sphenodon punctatus) has been protected by law since 1895.[15][16] A second species, the Brothers Island tuatara S. guntheri, (Buller, 1877), was recognised in 1989,[12] but since 2009 it has been reclassified as a subspecies (S.p. guntheri).[17][18] Tuatara, like many of New Zealand's native animals, are threatened by habitat loss and introduced predators, such as the Polynesian rat (Rattus exulans). Tuatara were extinct on the mainland, with the remaining populations confined to 32 offshore islands[19] until the first North Island release into the heavily fenced and monitored Karori Wildlife Sanctuary (now named "Zealandia") in 2005.[20]
During routine maintenance work at Zealandia in late 2008, a tuatara nest was uncovered,[21] with a hatchling found the following autumn.[22] This is thought to be the first case of tuatara successfully breeding in the wild on New Zealand's North Island in over 200 years.[21]
Taxonomy and evolution
Relationships of the tuatara to other living reptiles and birds, after Simões et al. 2022[23]
| Reptilia |
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Tuatara, along with other now-extinct members of the order Rhynchocephalia, belong to the superorder Lepidosauria, the only surviving taxon within Lepidosauromorpha along with 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.[24]
Tuatara were originally classified as lizards in 1831 when the British Museum received a skull.[25] The genus remained misclassified until 1867, when A.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.[26]
At one point many disparately related species were incorrectly referred to the Rhynchocephalia, resulting in what taxonomists call a "wastebasket taxon".[27] Williston proposed the Sphenodontia to include only tuatara and their closest fossil relatives in 1925.[27] However, Rhynchocephalia is the older name[26] and in widespread use today. Sphenodon is derived from the Greek for "wedge" (σφήν, σφηνός/sphenos) and "tooth" (ὀδούς, ὀδόντος/odontos).[28] Many scholars use Sphenodontia as a subset of Rhynchocephalia, including almost all members of Rhynchocephalia aside from the most primitive representatives of the group.[29]
The earliest rhynchocephalian, Wirtembergia, is known from the Middle Triassic of Germany, around 240 million years ago.[29] During the Late Triassic, rhynchocephalians greatly diversified,[10] going on to become the world's dominant group of small reptiles during the Jurassic period,[30] when the group was represented by a diversity of forms, including the aquatic pleurosaurs and the herbivorous eilenodontines.[30] The earliest members of Sphenodontinae, the clade which includes the tuatara, are known from the Early Jurassic of North America. The earliest representatives of this group are already very similar to the modern tuatara.[31] Rhynchocephalians underwent a great decline during the Cretaceous period,[32] possibly due to competition with mammals and lizards,[33] with their youngest record outside of New Zealand being of Kawasphenodon known from the Paleocene of Patagonia in South America.[34]
A species of sphenodontine is known from the Miocene Saint Bathans Fauna. Whether it is referable to Sphenodon proper is not entirely clear, but is likely to be closely related to tuatara. The ancestors of the tuatara were likely already present in New Zealand prior to its separation from Antarctica around 82-60 million years ago.[33]
Cladogram of the position of the tuatara within Sphenodontia, after Simoes et al., 2022:[35]