by Greg Mayer
Tuataras are in the news today, although there really isn’t that much new about them. In fact, as Natalie Angier points out in the New York Times, they are transparently Triassic in aspect, as the following picture, of a tuatara named Henry, will attest.
Angier provides a review of various interesting aspects of tuatara biology– they live a long time, reproduce slowly, eat giant orthopterans, are nearly extinct, etc. What’s most interesting about them is that they are the sole living members of one of the four major groups of extant reptiles, the Sphenodontida (an order in the Linnaean hierarchy of ranks, the other reptile orders being turtles, crocodiles, and snakes+lizards); and they are found only in New Zealand, where they are restricted to a few offshore islands. (They have recently been transplanted back to the mainland of New Zealand, whence they were extirpated centuries ago by introduced rats.)
Though they look much like lizards (iguanas or agamids in particular), and were thought to be lizards when first discovered, they are in fact not lizards, as anatomical examination reveals. They have a primitive type of skull, termed fully diapsid, which means the cheek region of the skull has two complete openings surrounded by bone, and they have at most a rudimentary hemipenis (the distinctive double copulatory organ that characterizes snakes and lizards).
Tuataras are a good example of an older group surviving on an isolated land mass, something typical of old islands like New Zealand, which separated from other parts of the former southern supercontinent of Gondwana around 80 million years ago. Tuataras had been spread about the globe during the Mesozoic (Age of Reptiles), but survived only on New Zealand.
It is distressingly common to see tuataras described as “dinosaurs”, but they are no such thing. They lived during the time of the dinosaurs (and have changed relatively little since, earning them the sobriquet “living fossils”), but their closest relatives are the lizards and snakes, together with which they form the larger reptilian group known as lepidosaurs. Dinosaurs closest living relatives are birds, which, indeed, are perhaps best thought of as actual dinosaurs themselves.