The word "dinosaur" is commonly used to describe an old person, but when it refers to a tuataras, the term is as literal as it is metaphorical. The two species of tuatara alive today are the only surviving members of an order which flourished about 200 million years ago — they are living dinosaurs. They are also among the longest-lived vertebrates on Earth, with some individuals living for anywhere between 100 and 200 years.