Sphenodon

Sphenodon is the only living representative of the order Rhynchocephalia, of class Reptilia. It was once widely distributed in the main islands of New Zealand but is now restricted to some small island in the Bay of Plenty, North Islands. As it shows many primitive features and shares some amphibian and reptilian characters, it is often called the ‘living fossil’ forming a sort of bridge between the two groups of vertebrates. Sphenodon is called ‘Tuatara’ by the natives. Sphenodon is a rather large lizard like reptile. It is nocturnal in habit and lives in burrows in the daytime. It feeds mainly on insects. Dorsally the body is dull olive green with yellow spots and ventrally it is whitish. Small granular scales cover the body, while on the ventral side there are transverse rows of large square plates formed by scales. A mid-dorsal row of scales forms spines (frill) from the head to the end of the tail, except on the neck. The tail is thick and laterally compressed. The eyes are large with vertical pupil. The males lack copulatory organs. The cloacal aperture is in the form of a transverse slit.

The skull of sphenodon consists of paired premaxillae, frontals, nasals and parietals. Three temporal fossae are present. The quadrate is fixed. The pterygoids extend forwards separating the palatines. Post-frontals are separate. Teeth are acrodont and are found in two parallel rows. The vertebrae are amphicoelous with persistent notochord. A pro-atlas is present between the skull and atlas bone. Ribs are single-headed and abdominal ribs are present. A median sternum is present. Caudal vertebrae have chevron bones. In the forelimbs radius and ulna are separate. A median interclavicles and a ventro-median procoracoid are present. A cartilaginous epipubis is present. The ilia are blade- like. The heart is of reptilian type. But the three principal arches arise from a short common trunk. The arterial and venous systems show similarities with those of Urodela. The brain has well-developed central hemispheres and optic lobes, but the cerebellum is poorly developed. There is a distinct ‘parietal eye’ with lens, retina and nerve connection with brain. In the adult the parietal foramen is covered with skin. It is the only reptile in which the male lacks penis. The eggs take about 13 months to hatch.

The anatomical features of sphenodon clearly indicate that it is a reptile, though primitive and almost ideally generalized. But its true systematic position has been a matter of controversy and opinions differ among the different zoologists.

Reference

1. Britannica Reference Encyclopaedia

2. Knowledge Encyclopedia Animal!: The Animal Kingdom as you've Never Seen it Before

3. Images are taken from Zoo-Que and Google.

4. In Defense of Plants: An Exploration Into the Wonder of Plants

5. A Naturalist’s Guide to the Birds of India

6. Earth: A Sustainable Planet

Also See

• Migration & Navigation of Birds

• Archaeopteryx – The First Bird`s Fossil

• Parrots

• Bats