Exaptation is the process by <u><em>which the features acquire those functions for which they were not originally selected</em></u> or adapted. Feather is an example of exaptation, it has appeared in various fossils of the flightless ancestors of modern birds, it later became important for flying, Once they molded for flying it adapted for that function, It is found in both behavior and anatomy.
They form under a pressure and heat that doesn't destroy the fossils. Igneous and metamorphic rock form from molten rocks thus reaching a temp that destroys the fossils within.
