The bat is the only native mammal in New Zealand. The short-tailed bat is the only one of its kind in the world. Like the tuatara and the New Zealand frog, the short-tailed bat is a living fossil. The other species of bat is the long tailed bat. This species immigrated relatively recently from Australia.
Bats are thought to have evolved from a "tree-living shrew-like mammal about 80-100 million years ago. To arrive in New Zealand, the bat would have had to travel from South America through West Antarctica and then cross the Southern Ocean.