The only indigenous mammals of Bermuda are five species of bats, all of which are also found in the eastern United States: Lasionycteris noctivagans, Lasiurus borealis, Lasiurus cinereus, Lasiurus seminolus and Perimyotis subflavus. Other commonly known fauna of Bermuda include its national bird, the Bermuda petrel or cahow. It was rediscovered in 1951 after having been thought extinct since the 1620s. It is important as an example of a Lazarus species. The government has a programme to protect it, including restoration of a habitat area. The Bermuda rock skink was long thought to have been the only indigenous land vertebrate of Bermuda, discounting the marine turtles that lay their eggs on its beaches. Recently through genetic DNA studies, scientists have discovered that a species of turtle, the diamondback terrapin, previously thought to have been introduced, pre-dated the arrival of humans in the archipelago. As this species spends most of its time in brackish ponds, some question whether it should be classified as a land vertebrate to compete with the skink's unique status.