Because of the lack of predators, even the bats spend most of their time on the ground. There are also about 60 species of lizard (30 of gecko and 30 of skink), and four species of frog (all rare and endangered). There are two species of tuatara, "Sphenodon", the only surviving reptile in its order. These living fossils are reptiles of a type which flourished as long ago as 200 million years. While mapping its genome, it has been discovered that the species has between five and six billion base pairs of DNA sequence. The reptile now lives only on the islands in the Cook Strait and the Bay of Plenty.