Tuataras

The tuatara is the only living descendant of a worldwide group of reptiles that first apear in the Jurassic period, in the early dinosaur era. While the rest of the group died out 60 million years ago, the tuatara has survived.

The tuatara is a reptile endemic to New Zealand which, though it resembles most lizards, is actually part of a distinct lineage, order Sphenodontia. The two surviving species of tuatara are the only members of their order, which flourished around 200 million years ago. Their most recent common ancester with any other extinct group is with the squamates (lizards and snakes). For this reason, tuatara are of great interest in the study of the evolution of lizards and snakes, and for the reconstruction of the appearance and habits of the eariest diapsids (the group that also includes birds and crocodiles).

Tuataras are greenish brown, and measure up to 80 cm (31 in) from head to tail-tip with a spiny crest along the back, especially pronounced in males. Their dentition, in which two rows of teeth in the upper jaw overlap one row on the lower jaw, is unique among living species. They are further unusual in having a pronounced parietal eye, dubbed the third eye.They have a unique feature in their skeleton, some of them apparently evolutionarily retain from fish. Although tuataras are sometimes called living fossils, recent taxonomic and molecular work has shown that they have changed significantly since the Mesozoic era.

Adult tuatara are terrestial and nocturnal reptiles, though they will often bask in the sun to warm their bodies. hatchlings hide under logs and stones, and are diural, likely because adults are cannibalistic. Tuataras thrive in tempertures much lower than those tolerated by most reptiles, and hiberante during winter. they remain active at temperatures as low as 5 C, while temperatures over 28 C are generally fatal. The optimal body temperature for the tuatara is from 16-21 C, the lowest of any reptile. The body temperature of a tuatara is lower than that of any other reptile ranging from 5.2-11.2 C over a day, whereas most reptiles have body temperatures around 20 C. The low body temperature results in a slower metabolism.

Burrowing seabirds such as petrels, prions, and shearwaters share the tuatara's island habitat during the bird's nesting season. The tuatara uses the bird's burrow for shelter when available , or dig their own. The seabird's guano helps to maintain invertebrate populations that tuataras predominantly prey on:including beetles, crickets, and spiders. Their diet also consists of frogs, lizards, and birds eggs and chicks. the eggs and young of seabirds that are seasonally available as food for tuataras may provide beneficial fatty acids. Tuataras of both gender defend territories, and will threaten and eventually bite intruders. The bite can cause serious injury. Tuataras will bite when approached, and will not let go easily.

Tuataras were long confined to 32 offshore islands free of mammals. The island are difficult to get to, and are colonised by few animal species, indicting that some animals absent from the mainland. However where kiore(Polynesian rat) have recently established on several of the islands, tuataras were persisting, but not breeding, on these islands. Additionally, tuataras were much rarer on the rat-inhabited islands.

The recent discovery of tuatara hatchlings on the New Zealand mainland indicate that attempts to re-establish a breeding population on the mainland have had some success. The total population of tuataras of all species and subspecies is estimated to be greater than 60,000, but less than 100,000.

In conclusion, with these low numbers of tuatara estimated to be left they could become an endangered species.