Academic Reading — Test 57

Reading passage

To the casual observer, the tuatara of New Zealand looks like an ordinary lizard. It has a scaly hide, a sturdy tail, clawed feet and a low-slung body that would not seem out of place among the geckos and skinks that share its habitat. Yet this resemblance is misleading. The tuatara is not a lizard at all, and biologists regard it as one of the most remarkable reptiles alive today. It is the sole surviving member of an ancient order called the Rhynchocephalia, a group that flourished alongside the dinosaurs more than two hundred million years ago. Every other species in that order has long since vanished, leaving the tuatara as a solitary representative of a once-diverse lineage. For this reason it is frequently described as a "living fossil", although scientists are careful to note that the animal has continued to evolve and is not simply an unchanged relic of the deep past. The differences between tuatara and true lizards lie chiefly in their skeletons and internal anatomy rather than in their outward appearance. One of the clearest distinctions is found in the skull. Lizards possess a flexible skull with a single opening behind each eye, and many can move parts of the skull independently when feeding. The tuatara, by contrast, retains two openings on each side of the skull and a rigid, fixed structure, a primitive arrangement that has been preserved almost unchanged for tens of millions of years. Its teeth are equally distinctive: rather than being set in sockets, they are fused directly to the jawbone and arranged in a way that produces a precise shearing action. A single row of teeth on the lower jaw fits neatly between two rows on the upper jaw, allowing the animal to slice through tough prey such as beetles, spiders and even the occasional seabird chick. Perhaps the most celebrated feature of the tuatara is its so-called third eye, a light-sensitive organ located on the top of the head. This parietal eye possesses a rudimentary lens and retina and is connected to the brain, though it becomes covered by scales as the animal matures and is not used for forming images. Researchers believe it may help the tuatara to regulate its exposure to sunlight and to track seasonal changes in daylight, thereby influencing the timing of breeding and other cycles. Although some lizards retain traces of a similar structure, in the tuatara it is unusually well developed, offering a window onto features that were probably common in early reptiles. The tuatara's biology is also shaped by the cool, temperate climate of New Zealand, and in this respect it differs sharply from most reptiles, which favour warm conditions. It remains active at temperatures that would leave many lizards sluggish or immobile, functioning comfortably at around twelve degrees Celsius. This tolerance of the cold is matched by an exceptionally slow pace of life. The tuatara grows gradually, may not reach breeding age until it is several decades old, and can live for well over a century. Females do not reproduce every year; instead they may lay eggs only once every four or five years, and those eggs can take more than twelve months to hatch, one of the longest incubation periods recorded for any reptile. As with many reptiles, the temperature of the nest determines the sex of the offspring, with warmer conditions tending to produce males. Once widespread across the New Zealand mainland, the tuatara suffered a catastrophic decline after the arrival of human settlers and the mammals they introduced. Rats, in particular, proved devastating, preying on eggs and young animals and competing for food. By the twentieth century the species survived only on a scattering of offshore islands that remained free of such predators. Conservationists have since worked to secure its future by clearing introduced mammals from selected islands and by establishing new populations in carefully managed sanctuaries, including some on the mainland. Captive breeding programmes have added a further layer of protection. Because the tuatara reproduces so slowly, recovery is a patient undertaking, and the animal remains dependent on continued human vigilance. Its survival matters not only for its own sake but because it preserves a unique branch of reptilian history that has no living equal anywhere on Earth.