The tuatara 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. The name tuatara is derived from the Māori language and means "peaks on the back".
The Lepidosauria is a subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata includes lizards and snakes. Squamata contains over 9,000 species, making it by far the most species-rich and diverse order of non-avian reptiles in the present day. Rhynchocephalia was a formerly widespread and diverse group of reptiles in the Mesozoic Era. However, it is represented by only one living species: the tuatara, a superficially lizard-like reptile native to New Zealand.
Rhynchocephalia is an order of lizard-like reptiles that includes only one living species, the tuatara of New Zealand. Despite its current lack of diversity, during the Mesozoic rhynchocephalians were a speciose group with high morphological and ecological diversity. The oldest record of the group is dated to the Middle Triassic around 238 to 240 million years ago, and they had achieved a worldwide distribution by the Early Jurassic. Most rhynchocephalians belong to the group Sphenodontia ('wedge-teeth'). Their closest living relatives are lizards and snakes in the order Squamata, with the two orders being grouped together in the superorder Lepidosauria.
Clevosaurus is an extinct genus of rhynchocephalian reptile from the Late Triassic and the Early Jurassic periods. Species of Clevosaurus were widespread across Pangaea, and have been found on all continents except Australia and Antarctica. Five species of Clevosaurus have been found in ancient fissure fill deposits in south-west England and Wales, alongside other sphenodontians, early mammals and dinosaurs. In regards to its Pangaean distribution, C. hadroprodon is the oldest record of a sphenodontian from Gondwana, though its affinity to Clevosaurus has been questioned.
Cynosphenodon is an extinct genus of rhynchocephalian in the family Sphenodontidae from the Middle Jurassic La Boca Formation of Tamaulipas, Mexico. It is known from a largely complete lower jaw and fragments of the upper jaw. It is suggested to be among the closest known relatives of the tuatara, with both being placed in the Sphenodontinae, which is supported by among other characters, the growth pattern of the teeth.
Eilenodon is an extinct genus of rhynchocephalian reptile from the Late Jurassic Morrison Formation of western North America, present in stratigraphic zone 4. The only known species of this genus is Eilenodon robustus. It was a member of a group of rhynchocephalians called the eilenodontines, which were large, herbivorous members of Rhynchocephalia, the order of reptiles which contains the modern tuatara (Sphenodon). The generic name "Eilenodon" is Greek for "packed teeth", in reference to its closely packed teeth. The specific name, "robustus", refers to the strong build of the jaws.
Gephyrosauridae is an extinct family of rhynchocephalians that lived in the Late Triassic and Early Jurassic. They are generally considered to be rhynchocephalians that lie outside of Sphenodontia, but in some analyses they are recovered as more closely related to squamates than to sphenodontians.
Gephyrosaurus is a genus of early rhynchocephalian first described and named in 1980 by Susan E. Evans. They are distantly related to the extant Sphenodon with which they shared a number of skeletal features including a large tooth row along the side of the palatine bone and posterior process of the dentary bone. The type species, G. bridensis, lived during Early Jurassic in Wales, UK. Whiteside & Duffin (2017) described the second species, G. evansae, known from a partial maxilla recovered from Late Triassic (Rhaetian) fissure fills in Carboniferous Limestone in Somerset. Gephyrosaurus, other potential gephyrosaurids and Wirtembergia are the only rhynchocephalians to lie outside Sphenodontia in modern definitions of the group, and have been found to be more closely related to squamates in some phylogenetic analyses.
Oenosaurus is an extinct genus of sphenodontian reptile from the Late Jurassic (Tithonian) aged Mörnsheim Formation of Germany.
Sphenotitan is an extinct genus of rhynchocephalian reptile, known from the Late Triassic (Norian) Quebrada del Barro Formation of Argentina. It is the earliest known member of the herbivorous Elienodontinae, and the only one known from the Triassic. It was a large-sized sphenodontian, with an estimated skull length of over 10 centimetres (3.9 in). The skull is roughly triangular in shape, and had large upper temporal fenestrae. The region of the skull in front of the eye socket is short. The premaxillae forms beak, with a cutting edge similar to a chisel. The teeth of Sphenotitan, like other elienodontines, were large and wide, and designed for shredding vegetation, with blade-like palatal teeth on the roof of the mouth.
Sphenovipera jimmysjoyi is an extinct species of sphenodontian dated from the Middle Jurassic. If was discovered in the lower part of the La Boca Formation located in Tamaulipas, Mexico. Only the lower jaw of this organism has been discovered and studied. It is possibly the only species of rhynchocephalian yet discovered to show evidence of venom delivery.
Opisthodontia is a proposed clade of sphenodontian reptiles, uniting Opisthias from the Late Jurassic-earliest Cretaceous of Europe and North America with the Eilenodontinae, a group of herbivorous sphenodontians known from the Late Triassic to Late Cretaceous.
Clevosaurs are an extinct group of rhynchocephalian reptiles from the Triassic and Jurassic periods.
Sapheosaurs are an extinct group of rhynchocephalian reptiles from the Late Jurassic period. "Sapheosaurs" is an informal name for a group of rhynchocephalians closely related to the genus Sapheosaurus. It was first recognized as a group containing multiple genera by Hoffstetter in 1955. The group has sometimes been given a formal taxonomic name as the family Sapheosauridae, although in some analyses this group belongs to the family Sphenodontidae and thus cannot be assigned its own family. They were fairly advanced rhynchocephalians which may have had semiaquatic habits.
Eilenodontinae are an extinct clade of reptiles belonging to Sphenodontia. They are either considered a subgroup of Opisthodontia, or Sphenodontidae. They had deep jaws with broad, closely packed teeth with thick enamel and noticeable wear facets. They were likely herbivorous, and probably chewed with a proal movement, with food shredded between the edges of opposing sharp-edged wear facets. Members of the group are known from South America, North America and Europe. The earliest known member of the group, Sphenotitan, is known from the Late Triassic of South America. while the youngest members are known from the Late Cretaceous of South America. The group contains some of the largest known sphenodontians, with Priosphenodon suggested to be the largest known non aquatic sphenodontian, with an estimated body length of over 1 metre (3.3 ft).
Kawasphenodon is an extinct genus of sphenodontian reptile, known from the Late Cretaceous and Paleocene of Patagonia in South America. The type species, K. expectatus, was described in 2005 from jaw fragments found in late Campanian aged sediments in the Los Alamitos Formation, the jaw when complete was estimated to be 11 cm long, making it among the largest known sphenodontians. A second species, K. peligrensis, around 1/3 the size of the type species, was described in 2014 also from jaw fragments in early Paleocene (Danian) sediments of the Salamanca Formation, making it the youngest known definitive representative of Rhynchocephalia outside of New Zealand. In the original description, it was found to be a member of Sphenodontidae, in some other subsequent analyses it was found to be a member of Opisthodontia. A 2020 analysis of rhyncocephalian relationships found it to be outside Opisthodontia, and instead a member of the Sphenodontinae as the closest known relative of the tuatara, with an estimated divergence between the two genera in the Early Cretaceous. Other subsequent studies have endorsed its placement as a member of Sphenodontidae. Like most other rhynchocephalians, the teeth are acrodont, with a deep dentary, and it probably had an omnivorous habit.
Sphenofontis is an extinct genus of sphenodontian reptile known from the Late Jurassic of Germany, with a single known species, S. velserae. It is known from a single nearly complete and articulated sub-adult specimen, found in the late Kimmeridgian aged Torleite Formation in Brunn quarry in Bavaria, Southern Germany. It is thought to be a close relative of the living tuatara, tentatively referred to Sphenodontinae.
Taytalura is an extinct genus of lepidosauromorph reptile from the Late Triassic of Argentina. It contains a single species, Taytalura alcoberi, which is based on a well-preserved skull from the fossiliferous Ischigualasto Formation. As a lepidosauromorph, Taytalura is a distant relative of modern lepidosaurs such as sphenodontians and squamates. Taytalura did not belong to any group of modern lepidosaurs, since it bears unique features, such as unfused bones in the skull roof and teeth which all sit loosely in a deep groove without sockets. Regardless, Micro-CT scanning reveals features of the skull previously only seen in rhynchocephalians. This suggests that the ancestral condition of the skull in lepidosaurs was more similar to sphenodonts than to squamates.
Tika is an extinct genus of sphenodontian from the Late Cretaceous Candeleros Formation of Argentina. The type species is Tika giacchinoi. It is considered to be closely related to the tuatara,, and a member of the Sphenodontinae. It is the oldest member of Sphenodontinae known from South America.
Navajosphenodon is an extinct genus of sphenodontid reptile from the Early Jurassic Kayenta Formation of Arizona, United States. It is known from a fully articulated skeleton, and is similar in many aspects to the extant tuatara, both belonging to the Sphenodontinae, including sharing a complete lower temporal bar. It is one of the oldest known sphenodontines.
