Several studies of feather development in the embryos of modern birds, coupled with the distribution of feather types among various prehistoric bird precursors, have allowed scientists to attempt a reconstruction of the sequence in which feathers first evolved and developed into the types found on modern birds. Feather evolution was broken down into the following stages by Xu and Guo in 2009
Pennaceous feather with an asymmetrical rachis
Single filament
Multiple filaments joined at their base to a central filament
Multiple filaments along the length of a central filament
Multiple filaments arising from the edge of a membranous structure
Multiple filaments arising from the edge of a membranous structure
FTF: bon scott