Tuatara

Class: Reptilia
Order: Rhynchocephalia
Family: Sphenodontidae
Genus: Sphenodon

Species: S. punctuates (Gray, 1842) (conserved name), S. guntheri Buller, 1877 S. diversum

Sphenodon_punctatus_in_Waikanae,_New_Zealand

Sphenodon punctatus in Waikanae, New Zealand. image: wikipedia


It looks like a lizard but not quite

The tuatara are reptiles endemic to New Zealand and which, although resembling most lizards, are part of a distinct lineage, order Rhynchocephalia. 

 The two species of tuatara are the only surviving members of their order, which flourished around 200 million years ago.

Cladogram showing relationships of extant members of the Sauria. Numbered items are: 1. Tuatara 2. Lizards 3. Snakes 4. Crocodiles 5. Birds. "Lizards" are paraphyletic. Branch lengths do not indicate divergence times. image: wikipedia

Their most recent common ancestor with any other extant 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 earliest diapsids (the group that also includes birds, dinosaurs, and crocodiles).

340px-Henry_at_Invercargill

A male tuatara named Henry, living at the Southland Museum and Art Gallery, is still reproductively active at 111 years of age. image: wikipedia

Description

Tuatara are greenish brown and gray, 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. 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 photoreceptive eye, the "third eye", which is thought to be involved in setting circadian and seasonal cycles. They are able to hear, although no external ear is present, and have a number of unique features in their skeleton, some of them apparently evolutionarily retained from fish. 

Although tuatara are sometimes called "living fossils", recent anatomical work has shown they have changed significantly since the Mesozoic era.

Origin of the name

The name "tuatara" derives from the Māori language, and means "peaks on the back".  As with many other Māori loanwords, the plural form is now generally the same as the singular in formal New Zealand English usage. "Tuataras" remains common in less formal speech, particularly among older speakers.

source/further infohttp://en.wikipedia.org/w/index.php?title=Tuatara&oldid=612240746