page_title: Tuatara
section_title: Description
hierarchical_section_title: Tuatara / Description
caption_attribution_description: A schematic of the skull of the tuatara (Sphenodon), based on [1], [2]and [3]. Skull of a tuatara, showing the complete temporal arches, and individual bones: 1 = premaxilla 2 = nasal 3 = prefrontal 4 = frontal 5 = maxilla 6 = postfrontal 7 = dentary 8 = postorbital 9 = jugal 10 = parietal 11 = squamosal 12 = quadratojugal and quadrate
context_page_description: Tuatara are reptiles endemic to New Zealand. Although resembling most lizards, they are part of a distinct lineage, the order Rhynchocephalia. Their name derives from the Māori language, and means "peaks on the back". The single species of tuatara is the sole surviving member of its order, which originated in the Triassic period around 250 million years ago and which flourished during the Mesozoic era. Their most recent common ancestor with any other extant group is with the squamates. For this reason, tuatara are of interest in the study of the evolution of lizards and snakes, and for the reconstruction of the appearance and habits of the earliest diapsids, a group of amniote tetrapods that also includes dinosaurs and crocodilians.
  Tuatara are greenish brown and grey, and measure up to 80 cm from head to tail-tip and weigh up to 1.3 kg 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 also unusual in having a pronounced photoreceptive eye, the third eye, which is thought to be involved in setting circadian and seasonal cycles.
context_section_description: The tuatara is considered the most unspecialised living amniote; the brain and mode of locomotion resemble those of amphibians and the heart is more primitive than that of any other reptile. The lungs have a single chamber and lack bronchi.
  Both species are sexually dimorphic, males being larger. Adult S. punctatus males measure 61 cm (24 in) in length and females 45 cm (18 in). The San Diego Zoo even cites a length of up to 80 cm (31 in). Males weigh up to 1 kg (2.2 lb), and females up to 0.5 kg (1.1 lb). Brother's Island tuatara are slightly smaller, weighing up to 660 g (1.3 lb).
  The tuatara's greenish brown colour matches its environment, and can change over its lifetime. Tuatara shed their skin at least once per year as adults, and three or four times a year as juveniles. Tuatara sexes differ in more than size. The spiny crest on a tuatara's back, made of triangular, soft folds of skin, is larger in males, and can be stiffened for display. The male abdomen is narrower than the female's.
caption: Skull of a tuatara, showing the complete temporal arches, and individual bones:premaxillanasalprefrontalfrontalmaxillapostfrontaldentarypostorbitaljugalparietalsquamosalquadrate
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