More ancient than the dinosaurs

THE TUATARA

Until three years ago I had never heard of the tuatara, one of the oldest living vertebrates on earth. Even then I would have probably continued in ignorance of this creature if I had not happened to be discussing reptiles with a New Zealand contractor at the time. We were talking about ancient creatures and dinosaurs, and she mentioned this native animal that apparently moved its head once every two days, this being the average total of its activity (something of an exaggeration, I later found out). Surprisingly, given the recent resurgence of interest in dinosaurs after Jurassic Park, there has been little in print about the tuatara, and yet it is even older than the dinosaurs.

What, then, is the tuatara? Simply put, it is a reptile that looks like a medium-sized lizard but belongs to its own order, the Rhynchocephalians ("beak-heads"), which contains but one family, the Sphenodontidae. The tuatara itself is the only species (properly, Sphenodon punctatus), but there were many more species millions of years ago. This last living representative of the order was itself managing quite well in New Zealand until the arrival first of the Maori about a thousand years ago, and then the white man 100-200 years ago. Both sets of settlers brought their own commensals with them, notably rats (in the case of the Maoris, the Kiore rats). These zoological invaders outbred the tuatara and other native fauna and preyed on the creatures' eggs, until the tuatara was only to be found on a few offshore islands. Happily this century the New Zealand government placed the tuatara under strict protection and indeed strove to eliminate non-native fauna (particularly rats) from the reptile's island habitats. Even so, vigilance is constant and the slow reproductive rate of the tuatara makes it unlikely that this fascinating animal will become widespread or even available to most zoos outside of its homeland.

When it was first discovered, the tuatara was in fact classified as a lizard, and at a glance it could be mistaken for an agamid or perhaps an iguanid. Anatomical differences, however, led to its separation into its own order. The most important differences are anatomical, in the way that the vertebrae are joined and the jaws. A more obvious feature, although not visible from the outside, is that the tuatara lacks the male reproductive organ found in all other male reptiles. Instead the male undergoes the ritual of courtship but instead of internally fertilising the female lays a spermatophore, or packet of sperm, for her to lower her cloaca onto. This is reminiscent of amphibian reproduction, especially in newts and salamanders. As with some lizards, the pineal eye is also highly developed. This "third eye" does have a rudimentary lens and retina, but is covered by skin and does not apparently distinguish visible objects. Instead it acts as a sort of light quality sensor, which can tell the progress of the seasons and thus control such behaviours as courtship. One final thing that sets the tuatara apart from the lizards is its extreme longevity, even by reptilian standards. Tuataras do not reach sexual maturity until the age of twenty and will normally live for 80-100 years - a lifespan surpassed only by the tortoises.

In the wild, tuataras are mainly nocturnal. They make their homes in burrows, often those left by indigenous petrels, and venture out at night to prey on various insects and occasionally the eggs of seabirds. Their food consumption is low, however, as their general rate of life, both physically in terms of metabolism and in behaviour, is slow. One other fascinating thing about the tuatara is that it can tolerate temperatures low enough to incapacitate or kill its reptilian relatives - the optimum for a tuatara is in fact about 55 F, an average autumn day in Great Britain. Like the marine iguana, it can slow its heartbeat down, but to an even more extreme degree, about 1-2 beats every few minutes. Interestingly, however, despite this apparent lethargy and a rather docile appearance, it has a strong and tenacious bite.

The tuatara is indeed a living mystery and in many ways is unique among reptiles. Those wishing to see one in real life in the UK should go to Chester Zoo, which has eight living tuataras which they are hoping to breed: apparently two of them have already formed a permanent bond. In some ways the UK, with its similar climate to the tuatara's natural habitat, would be a better place for captive tuataras than other rich countries with hotter temperatures. Whether or not these animals could be bred in enough numbers to be released outside of their protected area, of course, is a different matter. Even if they were proved to be harmless to other fauna and flora, it is doubtful whether they could compete with native wildlife, given their pace of life and slow reproductive rates. It is a pity, but there are plenty of other animals in similar predicaments. In the meantime, the tuatara's admirers can visit the websites below and check in herpetological and zoological books.

Links

Bruce Musico at the University of Michigan gives a good account of the natural history of the tuatara and has a good photograph.

Barbara Blanchard is the Captive Program Co-ordinator of Wellington Zoo for the tuatara. Visit this site for details of their recovery program to assist the tuatara in the wild.

King and Burke's Online Taxonomic and Geographic Reference contains not only the tuatara but also crocodiles and chelonians.

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