rachis

“The thickness of the rachis in some specimens is 3 microns thick. That’s less than the size of the average cell,” O’Connor says.

It had a magenta rachis down the center with soft green vanes that shimmered yellow and purple and blue depending on how you turned it.

But this specimen lacked the rachis; it just had barbs and barbules down its ribbonlike tail.

That is interesting because the rachis seems to aid in flight.

The finding suggests that the barbs and barbules evolved before the rachis in feathers.