If your interested in bird evolution, several different stages of there evolution have been documented recently, after finds in china. I suggest you
research, archaeopteryx the most famous link in the evolutionary chain, or tetrapteryx a particular favorite of mine that had feathers on all 4 of its
limbs and its tail and supports the theory that feathered flight evolved from trees, rather than ground up.
Wrote an exam paper on feathered flight a couple of weeks ago as part of my degree course. Would be happy to help, if you want some more info.

