Friday, December 21, 2012

Feathers - no connection between the dinosaurs and the birds.

Consider this chart and the text that accompanies it from here:
Click to enlarge:

"Feather evolution was broken down into the following stages by Xu and Guo in 2009:[65]
  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.[72]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)[65] modified with the findings of Foth (2011).[72] 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."

There is much to be said about this chart.
The major thing is that pennaceous feathers appear only in the paraves and oviraptors (oviraptors are secondarily flightless birds). Pennaceous feathers do not appear in the dinosaurs. The jump is from purported earlier stage "feathers" in the dinosaurs* to pennaceous feathers in the primitive birds.
This is noted by Prum and Brush:
"Feathers, however, are hierarchically
complex assemblages of numerous
evolutionary novelties—the feather follicle,
tubular feather germ, feather branched structure,
interacting differentiated barbules—that
have no homolog in any antecedent structures"
This is the Achilles Heel of the dino to bird theory:
There is no connection between the dinosaurs and the birds.

* purported to be early stage "feathers" but even that is a dino to bird biased interpretation 

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