Feather - Evolution - Evolutionary Stages

Evolutionary Stages

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:

1. Single filament
2. Multiple filaments joined at their base
3. Multiple filaments joined at their base to a central filament
4. Multiple filaments along the length of a central filament
5. Multiple filaments arising from the edge of a membranous structure
6. Pennaceous feather with vane of barbs and barbules and central rachis
7. Pennaceous feather with an asymmetrical rachis
8. Undifferentiated vane with central rachis

However, Foth (2011) showed that some of these purported stages (stages 2 and 5 in particular) are likely simply artifacts of preservation caused by the way fossil feathers are crushed and the feather remains or imprints are preserved. Foth re-interpreted stage 2 feathers as crushed or misidentified feathers of at least stage 3, and stage 5 feathers as crushed stage 6 feathers.

The following simplified diagram of dinosaur relationships follows these results, and shows the likely distribution of plumaceous (downy) and pennaceous (vaned) feathers among dinosaurs and prehistoric birds. The diagram follows one presented by Xu and Guo (2009) modified with the findings of Foth (2011). The numbers accompanying each name refer to the presence of specific feather stages. Note that 's' indicates the known presence of scales on the body.