Evolution and systematics

Tuatara are confusing animals. They certainly confused J. E. Gray of the British Museum, when, in 1831, he described the skull of a tuatara as a species of Agamidae. Then, in 1840, when a whole tuatara came to hand, he placed it in a separate genus from the one assigned to the previously described skull. It was Gray's successor at the British Museum, Albert G√ľnther, who realized, in 1867, that tuatara belonged to an array of fossils in an order of its own, today referred to as Sphenodontia.

The sphenodontians have a fossil record of about 225 million years and, as a group, were most diverse in the late Tri-assic and Jurassic 180-220 million years ago, when they inhabited Europe, Africa, and North America. Sphenodontians were already in decline during the age of the dinosaurs, and almost all of them became extinct by the early Cretaceous. A single lineage in the family Sphenodontidae survived on a landmass that separated from the southern continent of Gond-wana 60-80 million years ago. This lineage gave rise to tuatara, and the Gondwanian fragment now forms the islands of New Zealand. Whether the tuatara have changed significantly from their ancient ancestors is unclear, however. No early sphen-odontids have been found in the New Zealand fossil record.

The name tuatara was bestowed by the Maori people when they arrived in New Zealand about 1,000 years ago. In the Maori language, tuatara is both a singular and plural noun. Two living species are recognized: Sphenodon guntheri (Buller, 1877) and Sphenodon punctatus (Gray, 1842). Within S. punc-tatus there are two distinguishable genetic forms.

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