a feature that performs a function but that was not produced by natural selection for its current use.
A good example of an exaptation is the use of feathers because originally feathers were meant to provide insulation y natural selection to bird, but overtime feathers became a feature that allowed for birds to fly. Also, the penguin being a flightless bird was given wings that were meant to fly but overtime they converted to flippers which allows it to swim in the oceans.
Another example is found in the skulls of vetebrates. Skulls contain sutures which are joints that fuse over time. Their purpose is allow for growth & development of the brain, but they also enable an easier birthing process aloowing the compression of the skull when the offspring is passing through the birth canal.Reference: Parry, W. (2013). Exaptation: how evolution uses what's available. Live Science. Retrieved from http://www.livescience.com/39688-exaptation.html