1.   Some, like goldfinches and redpolls, grow more feathers in winter and fluff them out in the cold for added insulation.

2.   They grew feathers.

3.   As many years went past, these beasts gradually grew feathers, giving themselves the power of flight to make the most of their new habitat.

4.   One theory is that dinosaurs grew feathers to keep warm or to use as an impressive display in mating or defence.