A hedgehog is any of the spiny mammals of the subfamily Erinaceinae, in the order Eulipotyphla. There are seventeen species of hedgehog in five genera, found through parts of Europe, Asia, and Africa, and in New Zealand by introduction. There are no hedgehogs native to Australia, and no living species native to the Americas (the extinct genus Amphechinus was once present in North America). Hedgehogs share distant ancestry with shrews (family Soricidae), with gymnures possibly being the intermediate link, and have changed little over the last 15 million years. Like many of the first mammals, they have adapted to a nocturnal way of life. Hedgehogs' spiny protection resembles that of the unrelated rodent porcupines and monotreme echidnas.