Geological analyses have suggested that New Zealand may have been entirely under water as recently as 28 Mya, making it impossible for flightless birds to have survived. However, the discovery of a "Sphenodon" fossil dating to the Early Miocene 19–16 Mya raises question as to whether the island mass was completely submerged. This finding offers further evidence that ancient "Sphenodon" species lived on some portion of the land mass since it separated from Gondwana approximately 82 Mya. Evidence of a sea level rise submerging much of New Zealand is generally accepted, but there is a debate about how much of New Zealand was submerged. A "Sphenodon" species surviving on a remnant part of the island suggests that larger species may have survived as well.