Tuatara

Order Rhynchocephalia is represented in the present time by only one genus known as Sphenodon or Hatteria commonly known as tuatara found in New Zealand. It appears to be on the verge of extinction and is protected by a special law in that country. The animals inhabit burrows and are nocturnal and carnivorous.

Sphenodon is a lizard like reptile up to two feet long with a well developed laterally compressed tail and pentadactyle limbs adapted for walking. The upper surface is covered with small granular scales and a crest of compressed spine like scales runs along the whole mid-dorsal line. The ventral surface is covered with tranverse rows of large squarish plate like scales.

Vertebrae are amphicoelous with remnants of notochord in the cavities between the centra. Intercentra are represented by bony elements or inferior arches known as chevron bones. In addition to atlas and axis there is another small median bone, the proatlas between atlas and axis occipital region of the skull. The caudal vertebrae are divided by a septum and the tail when lost is reproduced. Ribs are single headed and some of them possess cartilaginous uncinate processes as in birds. In the caudal region ribs are fused with vertebrae. There is a median sternum with coracoid and interclavicle attached at the anterior end. A series of ossifications, the abdominal ribs, lie in the wall of abdomen in the form of numerous transverse rows of small splint bones between the sternum and the pelvis.

Skull differs from that of lizard. There are two complete temporal fossae. The large supra-temporal fossa is separated below from the lateral temporal fossa by a bar of bone, the superior temporal arch or arcade, formed by postorbital and sequamosal. The lateral temporal fossa is bounded below by a slender bony bar, the inferior temporal arch, formed by long narrow jugal with a small quadrato jugal. The lateral fossa is separated from the orbit in front by a bar of bone formed by jugal and post orbital and is bounded behind by a posterior temporal arch formed of parietal and squamosal. Quadrate is immovably fixed. Premaxillae are not fused together. There is a well developed broad plate formed by plate like vomers, palatines and pterygoids. The dentary pieces of the mandible are united by ligament and not by suture.

The coracoid is attached to the sternum and is without fenestra. There is a T-shaped intercalvicle and a clavicle. Humerus is provided with an entepicondylar foramen present above the inner condyle of humerus and an ectepicondylar foramen present above the outer condyle of humerus. There are eleven carpal bones; four, including a pisiform, in the proximal row, two centrals and five in the distal row. In the pelvis, pubes are united in symphysis, in front of which is a cartilaginous epipubis. A large oval formen intervenes between ischia and pubis. A cartilaginous hypoischium is attached to the ischia behind. In the tarsus, tibiale and fibular elements are distinct though firmly united. There are five digits on each limb.

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