Finch beaks loom large in classical Darwinian theory, but two examples of mouth parts in very different animals show that dramatic variations can be achieved quickly without the slow and gradual accumulation of small changes Darwin envisaged.
Global Positioning System (GPS): that's a function. Maintaining a suite of satellites is one method for achieving the function. But there are other ways to figure out where in the world you are, and two very different animals show the way – naturally – using Earth's global magnetic field.