Order Rhynchocephalia
Suborder Sphenodontida


Family Sphenodontidae (Tuataras)

The Tuataras are the only surviving members of the order Rhynchocephalia. All other members of the order (and family) are known only from the Mesozoic.

Photo: Sphenodon punctatus, the "Tuatara". © Helen Gilks / Albert Aanensen/BBC NHU Picture Library / ARKive (by permission).

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Description: Adult tuataras are brownish-olive, and has a small yellow spot in the center of each scale. Enlarged scales form a crest down the back and tail. Sphenodon and the crocodilians resemble each other and differ from all other living reptiles in that they have diapsid skulls, which have both dorsal and temporal fossae with their bounding arches. Teeth are pesent on the premaxillary, maxillary, palatine, and dentary, and vestigially on the vomer. Well-developed gastralia are present. The male lacks a copulatory organ. The cloacal opening is a transverse slit. A nictating membrane, or third eyelid, can be moved slowly across the eyeball from the inner corner of the eye outward while the upper and lower lids remain open. A well-developed parietal eye, with small lens and retina, is present on top of the head. In the young it can be seen clearly through the translucent covering scale, but in the adult the skin above thickens. However, this is not a unique feature of the Tuatara. A similar structure is present in many lizards.

Size: The adult Tuatara is about 50 to 80 cm long (weigth up to 1 kg). Male Tuataras are larger than females

Distribution: New Zealand (only).

Habitat: Tuataras live in close association with vast colonies of nesting shearwaters (Pelecanoides urinatrix ), called Mutton Birds by the New Zealanders. These birds nest in underground burrows, which they share with the Tuataras.

Food: Insects, earthworms, snails. Occasionlly feeds on eggs or nestling birds and other lizards.

Age: On New Zealand, Tuataras have been kept in captivity for 77 years

(Thermal) Behavior: The Tuatara remains in its burrow during the day and prowls at night, when the temperature drops sharply and cold gusts of wind sweep over the islands. These animals are active at lower temperatures than other reptiles, and their body temperatures tends to be lower than that of their surroundings. Body temperatures ranging from 6.2 to 13.3 degrees Celsius have been reported in nature. The preferred temperature seems to be about 12 degrees Celsius.

It has been reported that Sphenodon is able to produce barking or croaking sounds. It can shed its tail like other lizards, e.g. when males are fighting.

Reproduction: Because of the low temperatures on New Zealand and hence the slow growth, Tuataras may be sexually mature when they are about 20 years old. Mating has been observed both in the field and in the laboratory. Insemination takes place by simple cloacal apposition. During the summer (which, south of the equator, is from November to January) the female lays about ten (up to 15) white, hard-shelled, elongate eggs about 28 mm long. They are usually deposited well away from the home burrow, in a shallow hole in sand where they can be warmed by the sun. By August, the embryos are nearly mature. However, the late-stage embryo apparently undergoes a sort of estivation over the second summer, and does not hatch until it is about 13 months old. During this estivation period, the nasal chambers become blocked with a proliferating epithelium that is resorbed shortly before hatching.

Phylogenetic relationships: Sphenodontian reptiles successfully radiated during Triassic and Jurassic times, but were driven almost to extinction during the Cretaceous period. The sparse Early Cretaceous record of sphenodontians has been interpreted as reflecting the decline of the group in favour of lizards, their suspected ecological successors. However, recent discoveries in Late Cretaceous beds in Patagonia partially modify this interpretation. Numerous skeletons of a new sphenodontian, Priosphenodon avelasi, were collected from a single locality in the Cenomanian&endash;Turonian Candeleros Formation, where it is more abundant than any other tetrapod group recorded in the quarry (for example, Crocodyliformes, Serpentes, Dinosauria and Mammalia). Adult specimens of Priosphenodon reached one metre in length, larger than any previously known terrestrial sphenodontian. Apesteguía & Novas (2003) proposed, using available evidence, that sphenodontians were not a minor component of the Cretaceous terrestrial ecosystems of South America, and that their ecological replacement by squamates was delayed until the early Tertiary. The new discovery helps to bridge the considerable gap in the fossil record (around 120 million years) that separates the Early Cretaceous sphenodontians from their living relatives (Sphenodon).

References:

Apesteguía, S. & Fernando E. Novas (2003)
Large Cretaceous sphenodontian from Patagonia provides insight into lepidosaur evolution in Gondwana.
Nature 425: 609-612

Goin,C.J., Goin,O.B. & Zug,G.R. (1978)
Introduction to Herpetology, 3rd ed.
W.H. Freeman & Co., San Francisco
ISBN 0-7167-0020-4

 

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Created: 12 Jan 1996 / Last changed: 7 Oct 2003