 It has survived ice ages, volcanic eruptions and the intrusion of humans on its South Pacific island home, but New Zealand's last survivor of the dinosaur age may become extinct due to global warming. Mounted with spiny scales from head to tail and covered by rough, grey skin that disguises them among the trees, the tuatara is one of the world's oldest living creatures. But the lizard-like reptile is facing increasing risk of extinction from global warming because of its dependency on the surrounding temperature which determines the sexes of unborn young while still in their eggs. "They've certainly survived the climate changes in the past but most of them (past climate changes) have been at a more slower rate," said Jennifer Moore, a Victoria University researcher investigating the tuatara's sexual behaviour. "So you wouldn't expect these guys to be able to adapt to a climate that's changing so rapidly." The sex of a tuatara depends on the temperature of the soil where the eggs are laid. A cooler temperature produces females, while a warmer soil temperature results in male offsprings. So named by New Zealand's indigenous Maori people because of the spines on its back, the tuatara is the only survivor of its species of reptile that flourished during the age of the dinosaurs, some 200 million years ago. It can grow up to 50 centimetres (20 inches) and weigh up to one kilogram (2.2 pounds) and like its reptile relative, the turtle, the slow-moving tuatara can live more than 100 years, feeding mainly on insects. But scientists say its long life span as well as its four-year breeding cycle -- relatively slow for a reptile - will make the adaptation process more difficult. According to Moore, a temperature above 21.5 degrees Celsius (71 degrees Fahrenheit) creates more male tuatara while a cooler climate leads to females. Already male tuatara on a tiny predator-free island near the top of New Zealand's South Island outnumber females by 1.7 times, Moore explained. Thanks to its geographic isolation, New Zealand is home to a host of unique wildlife, such as the flightless kiwi bird. But most have come under threat since the arrival of humans, starting with the Maori about 1,000 years ago then European settlers in the 19th century. Some indigenous species, such as the giant moa bird, went extinct because of overhunting and the introduction of predators, such as rats, dogs, and weasels. But New Zealand today is known as a leader in wildlife conservation, saving the likes of the Chatham Islands black robin from extinction. In 1980 there were just five black robins, now there are about 250. Peter Gaze, a senior conservation officer at the Department of Conservation, says global warming has become a new challenge for many of New Zealand's wildlife. "I think the impact of temperature change is widespread and diverse," he said. He says rare species such as the rock wren -- ancient, tailless birds found only in the South Island mountain ranges -- could become extinct if the warmer climate lets predators, like rats, to live in higher altitudes. The UN Intergovernmental Panel on Climate Change, the world's top authority on global warming, predicted in a report in February that global temperatures would rise by 1.8 to 4.0 degrees Celsius (3.2-7.2 Fahrenheit) this century. It also warned that between 20 to 30 percent of plant and animal species face an increased risk of extinction if the rise in the average global temperature exceeds 1.5-2.5 degrees Celsius. Once found throughout New Zealand, the tuatara is now limited to around 30 isolated islands. Alarmed by the rapid decrease, New Zealand has listed the tuatara on its endangered species list and has bolstered their numbers through artificial breeding and returning them to uninhabited islands eradicated of predators. Scientists say the tuatara population has recovered to around 50,000-60,000, but the little dinosaurs may find themselves giving birth only in laboratories if temperatures continue to climb. "The easiest way for the tuatara to survive would be for nesting female tuatara to change their behaviour and modify the areas where they nest, such as laying eggs deeper in the soil," Victoria University's Moore said. "There is a possibility that they will be able to adapt but I think the problem is that temperatures may rise so quickly they won't have time."