Friday, February 10, 2012

* No antecedent structures in dino to bird theory
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 [dinosaur] structures

(Brush 1993, 1996, 2000; Prum 1999). Genuine
evolutionary novelties are distinct from
simple microevolutionary changes in that they
are qualitatively or categorically different from
any antecedent or homonomous structure.
"In conclusion, the morphological and
molecular developmental details shared by
avian feather and scales support homology
between these structures at the level of the
placode. The morphology and development
of all subsequent structures within the feather
are evolutionary novelties that have no homologs
in avian or reptilian scales.
 "Many features of feathers and feather development meet this definition and qualify as evolutionary novelties. The follicle, the differentiated sheath and feather germ, differentiated barb ridges, barb rami, barbules, differentiated pennulae of the proximal and distal bar bules, and the rachis are all evolutionary novelties, as are the derived mechanisms by which these novel structures develop. At a molecular level, the derived 10 kilodalton -keratins of feathers are also novel"

In regards to the feather, the dino to bird theory (according to Prum and Brush) depends on a series of miracles (aka "numerous evolutionary novelties that have no homolog in any antecedent structures").
The pterosaur to bird theory is not based on miracles.

1 comment:

  1. Instead of "miracles" we could say "a series of magical events".