preadaptation

In biology, the fortuitous possession of a characteristic that allows an organism to exploit a new situation. In many cases, the characteristic evolves to solve a particular problem that a species encounters in its preferred habitat, but once evolved may allow the organism to exploit an entirely different situation. The ability to extract oxygen directly from the air evolved in some early fishes, probably in response to life in stagnant, deoxygenated pools; this later made it possible for their descendants to spend time on land, so giving rise eventually to the air-breathing amphibians.