THE EXTINCTION OF TUATARAS WILL NOT BE OUR FAULT

by Whit Gibbons

April 7, 2003

The tuatara of New Zealand is a species on the verge of extinction. Unlike with most other pending extinctions around the world, humans are not to blame.

Tuataras are the sole surviving members of an otherwise extinct taxonomic group of reptiles. For comparison among living reptiles, crocodiles and alligators have the smallest number of species, with fewer than 25. The turtles have more than 250 species, the snakes more than 2,700, and the lizards more than 4,400. Tuataras are distinctive in being lonely reptile relicts of the past. A hundred million years ago, tuataras would not have been considered particularly unusual 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 somewhat like iguanas that are brown instead of green but differ from all lizards by having distinctive dental, skull, and skeletal features. They also have blood cells that 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 will die at temperatures much above 80, are active at temperatures around 45, and can tolerate temperatures near freezing with no problem.

Tuataras reach lengths greater than two feet but 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 cannot even be transported to zoos, and the few captives living in zoos today are often not on display. 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 as a captive 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.

One of 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, young, and possibly even adults 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.

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. But all the species of tuataras have been on their way to extinction for millions of years, and the majority have already disappeared naturally.

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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