Despite this general picture, there have been birds who lost the power of flight soon after flight evolved. The first fossil flightless birds occurred in the Cretaceous period. It has long been recognised that there are circumstances where it is definitely not a good thing to have wings. The connection between oceanic islands and flightlessness was known to Darwin. The explanation is that, first, oceanic islands have few predators. Second, that storms occur which may blow winged birds right off the island so far that they cannot find they way back. Once they lose flight, the land birds can evolve to be larger and heavier, and many do so. "Phorusrhacos" became a dominant land carnivore.