Tuatara - Sphenodon Punctatus

Tuataras, and their sister group Squamata (which includes lizards, snakes and amphisbaenians), belong to the superorder Lepidosauria, the only surviving taxon within Lepidosauromorpha. Squamates and tuataras both show caudal autotomy, loss of the tail-tip when threatened, and have a transverse cloacal slit. The origin of the tuatara probably lies close to the split between the Lepidosauromorpha and the Archosauromorpha. Though tuatara resemble lizards, the similarity is mostly superficial, since the family has several characteristics unique among reptiles. The typical lizard shape is very common for the early amniotes; the oldest known fossil of a reptile, the Hylonomus, resembles a modern lizard.

Tuataras were originally classified as lizards in 1831 when the British Museum received a skull. The species remained misclassified until 1867, when Albert 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.

During the years since the inception of the Rhynchocephalia, many disparately related species have been added to this order. This has resulted in turning the rhynchocephalia into what taxonomists call a "wastebin taxon". Sphenodontia was proposed by Williston in 1925. Now, most authors prefer to use the more exclusive order name of Sphenodontia for the tuatara and its closest living relatives.

Sphenodon punctatus Sphenodon punctatus, drawing from unknown period

There are two extant species of tuatara: Sphenodon punctatus and the much rarer Sphenodon guntheri, or Brothers Island tuatara, which is confined to The Brothers Islands in Cook Strait. The Brothers Island tuatara have olive skin with yellowish patches. Sphenodon punctatus has two subspecies: the Cook Strait tuatara (unnamed subspecies), which lives on other islands in and near Cook Strait, and the northern tuatara (Sphenodon punctatus punctatus), which lives on the Bay of Plenty, and some islands further north.

Tuataras have been referred to as living fossils This means that they have remained mostly unchanged throughout their entire history, which is approximately 200 million years. However, taxonomic work on Sphenodontia has shown that this group has undergone a variety of changes throughout the Mesozoic. Many of the niches normally associated with lizards were instead held by sphenodontians. There was even a successful group of aquatic sphenodontians known as pleurosaurs, which differed markedly from living tuataras. Tuataras show cold weather adaptations that allow them to thrive on the islands of New Zealand; these adaptations are probably unique to tuataras and not present in extinct sphenodontians, which lived in much warmer climates.

This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

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