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Re: New feather-like fossil from the Jurassic of Kazakhstan, Dzik et al 2010



evelyn sobielski <koreke77@yahoo.de> wrote:


> It may be correct, it may be utter bollocks; I am not aware of any data that 
> resolves this at the moment. Though it seems to me that more data weights 
> towards the
>  latter.


I take the completely opposite view.  The current evo-devo hypothesis
spearheaded by Prum and Brush appears well supported, with evidence
marshalled from both the fossil record and molecular studies.  I would
certainly not characterize this hypothesis as "bollocks".


> The "type I to type V" transition scheme (if that's what you mean by 
> mainstream model) still assumes genetics hasn't progressed since the model's 
> inception (in
> other word, it has not accomodated a lot of crucial facts that were 
> established since its inception) and does not seem to map well on the fossil 
> record.


As pointed out by Brad, all hypothetical stages have been documented
in the fossil record.


> Undisputable evidence of stages III and IV has not, I think, been found yet, 
> and these stages would quite likely be the least advantageous (don't keep you 
> warm well,
> can't flutter-hop with them, maintenance is a nightmare and energy 
> expenditure considerable), killing hopes of progress to stage V dead. But 
> stage V has been
> realized at least once and quite possibly more often, perhaps far more often.


As for the contention that the evo-devo hypothesis is teleological,
with certain stages being inherently maladaptive; again, where is the
evidence for this?  In fact, as pointed out by Prum (2005), all
hypothetical morphological stages can be found among real feathers of
modern birds.  This directly refutes the contention that certain
stages are selectively disadvantageous, and are therefore non-viable
as intermediate morphologies.


Certain stages may have arisen through drift rater than positive
selection.  Prum goes on to say:

        "[F]eather evolution was likely characterized by periods
         in which a diversity of functionally redundant, selectively neutral
         variations in appendage structure were maintained in the phenotype
         rather than by a uniform history of natural selection for a
single function."


> We know that avian foot scales can be induced to grow into feather-like 
> structures.


This may be true.  Nevertheless, there is compelling evidence that
feathers did *not* evolve from scales, but are evolutionary novelties.
 Again, from Prum (2005):

       "Over the last half of the 20th century, neo-Darwinian approaches
       to the origin of feathers, exemplified by Bock (1965), have
       hypothesized a microevolutionary and functional continuum between
       feathers and a hypothesized antecedent structure (usually an
       elongate scale). 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 (Brush 1993, 1996, 2000; Prum 1999)."



Reference:


Prum. R.O. (2005) The evolution of feather diversity and function: Exaptation,
functional redundancy and historical contingency.  In: Briggs, D.E.G. (ed.)
Evolving Form and Function: Fossils and Development. pp 245-256.



Cheers

Tim