It is believed that the ancestors of the tuataras reached New Zealand 140 million years ago (right around the close of the Jurassic), but no actual fossils dating back more than 25 thousand years have been found. These fossils show that the tuatara used to range throughout the two main islands of New Zealand. Now though, they are restricted to 30 small islands off the northeast coast of the North Island and in Cook Strait. Half of these islands measure a mere 25 acres or less.
Most tuatara inhabited islands are not researcher friendly, being partially or entirely cliff-bound, they are frequently exposed to strong winds which stunts the native vegetation. It has been noted that many tuatara inhabited islands are also home to small sea birds like petrels and shearwaters. It has also been noted that these birds play a vital role in tuatara life. For they both provide housing and food for these reptiles. A petrel burrow complete with guano makes not only for a good place to sleep, but also a nice breeding ground for invertebrates, which comprise a large portion of tuatara diet.
Although inverts are a large portion of the food, adult animals are quite capable of taking down and eating the adults, chick and eggs of the many petrels that live on the islands.