NOT ALL EXTINCTIONS ARE OUR FAULT

by Whit Gibbons

January 25, 2009


Over the eons millions of species have gone extinct naturally, but in modern times humans are generally the cause of species declines. However, unlike most other pending extinctions around the world, humans are not to blame for the imminent extinction of the tuatara of New Zealand.

Tuataras are the sole surviving members of an otherwise extinct taxonomic group of reptiles. For comparison with other living reptiles, more than 7000 species of snakes and lizards are alive today. A hundred million years ago, tuataras would not have been considered rare because, as verified by the fossil record, hundreds of species thrived throughout the world. Today they are restricted to living on only a few cold, undeveloped islands off the New Zealand coast.

Tuataras look like big brown lizards but differ from them by having distinctive dental, skull, and skeletal features. Their blood cells are larger than any other living reptile. Tuataras have the remnants of a third eye in the center of the skull, and although a similar structure has been studied in some lizards, the function remains unknown. Another tuatara trait also found in a few lizards is vocalization. Hearing a tuatara croak on a cold, drizzly night on an uninhabited island a thousand miles from Australia would presumably bring back some strange emotions related to our own evolutionary past. They reportedly make a cricket-like sound when picked up.

A distinctive physiological difference between tuataras and all other living reptiles is that they require cool temperatures. A well-known characteristic of other reptiles is that they are only active when they are warm. Most reptiles do well at temperatures between 70 and 80 degrees F, and some desert lizards thrive at temperatures above 100. But a tuatara tolerates temperatures near freezing and is active around 45 degrees but will die at temperatures much above 80.

Tuataras reach lengths greater than two feet. They eat mostly small animals, such as insects, snails, and frogs. They also eat bird eggs and a few small seabirds that nest on their islands. Tuataras are classified as endangered and are carefully protected. They are not allowed to be transported out of the country, even to zoos. Most Americans have never seen a live one, and most New Zealanders have never seen one in the wild, as the islands themselves are practically inaccessible.

Tuataras have a long life span. One was kept in captivity for 77 years, and documentation that some individuals live more than a century would come as no surprise. Other age-related phenomena of importance are that these bizarre animals take up to two decades to reach maturity and more than half a century to attain full adult size. Female tuataras lay about a dozen eggs, but at intervals of four years. The eggs take as many as 15 months to hatch.

Among the greatest threats to the remaining tuataras are non-native rats that have been inadvertently introduced to the islands. A slow-growing reptile with a low reproductive output that has also evolved without natural predators can become dependent on extended longevity to assure successful reproduction. The presence of a new predator that can kill eggs and young could become a serious threat to the tuatara's continued existence. In fact, the sad news is that these unusual reptiles are already extinct on some of the islands invaded by rats. Some conservation biologists contend that humans are culpable for the introduction of rats and the decline of tuataras. Sure, we have probably caused the disappearance of some tuataras, but these last remnants of this bizarre group of reptiles were on the way out the door to extinction long before humans appeared on the scene. The majority of the species of tuatara had already disappeared naturally millions of years ago.

Tuataras represent a conservation situation different from ones that pit economics against the environment or politicians against public sentiment. Humans protect today's tuataras as well as a wild animal can be protected. Other species of wildlife and other environments have been woefully neglected or actively mistreated by humans in many ways on a global scale, but when the last tuatara dies, we really should not blame ourselves.


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