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Fw: Dinosaur Revolution Review



Resent due to the (apparently Yahoo) snipper demon.



----- Forwarded Message -----
> From: Jura <pristichampsus@yahoo.com>
> To: "dinosaur@usc.edu" <dinosaur@usc.edu>
> Cc: 
> Sent: Thursday, 15 September 2011 9:40 PM
> Subject: Re: Dinosaur Revolution Review
> 
> ----- Original Message -----
> 
>>  From: Scott Hartman <skeletaldrawing@gmail.com>
> 
> 
>  
>>  For example (parting ways now) I consider the ease with which breeders
>>  have grown feathers sticking out from scales in a few short decades
>>  (centuries?) to show it's really not challenging to produce an
>>  intermixed dermal type with feathers (or fuzz) and scales.  Yes, it's
>>  very uncommon in extant birds, but I consider that a derived condition
>>  that saves on metabolic cost (birds have long since lacked a need for
>>  scales on most of the body, so why not make sure there's a gene to
>>  prevent them from being grown where they aren't needed).
> 
> ++++++++++++++++++++++++++++++++++++++
> 
> Maybe yes, maybe no, but these breeds are also associated with brachydactyly, 
> and occasional polydactyly. The latter might be a case of artificial 
> selection 
> causing a pleiotropic effect, but the former has been at least linked to the 
> ptilopody genotype (though the interaction might be more epigenetic). The 
> point 
> being that one should be cautious about using artificially selected breeds 
> that 
> often express one trait do to the deformation of others. To put it another 
> way: 
> I doubt that six toed theropods were a common phenotype during feather 
> evolution 
> either. 
> 
> While the lack of scale plasticity in extant birds may very well be a derived 
> trait, I still can't help but wonder about the old "party line" 
> regarding why scales were lost in the first place (i.e. the weight reduction 
> hypothesis). With the exception of osteoderms, scales are not that heavy. 
> Birds 
> get away with flying around with all kinds of strange display structures that 
> would weigh more than a light covering of scales would. Has anyone ever 
> really 
> test 
 The scales angle would be hard, but 
> one could try at least test the other trait that is often argued to have been 
> lost do to weight reduction (teeth). In that case it would just require 
> gluing 
> teeth to the bills of some flapping birds and then looking at the change in 
> flight costs associated with it. There have already been similar studies 
> using 
> "feather extensions." Anyway I'm going even further off subject. 
> The point I'm making here is that I think the weight
> reduction hypothesis is one that is way overused, and undertested.
> 
> ___________________________________________________
> 
> 
> If one insists upon a
>>  hardline "mutual exclusivity" hypothesis like Jason advocates 
> then you
>>  must assume that the line to feathered dinosaurs had to first evolve
>>  naked patches of skin before any form of dino-fuzz could even exist.
>>  I can't say that's impossible, but it seems much more plausible (to
>>  me) that there were many permutations of co-existing feathers and
>>  filamentous structures (perhaps some of them like those seen  in
>>  Psittacosaurus and Tianyulong).  With scales and filaments co-existing
>>  (perhaps at times just restricted to different parts of the body) then
>>  losing them in lineages is simple, and does not require the
>>  re-evolution of scales in those areas.  It could be that only after
>>  truly extensive feathering evolved (perhaps even after flight evolved
>>  and weight-savings became more of an issue) that there was a selective
>>  pressure that favored making scales and feathers developmentally
>>  exclusive (a condition that is still easily overcome even today via
>>  artificial selection).
> 
> 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 
> Just to clarify, the evolution of feathers from scales would not actually 
> require a naked stage. Our current understanding of feather morphogenesis 
> suggests that feathers came about by hijacking the scale developmental 
> pathway. 
> In this case, all that would need to happen would be one, o
in codon deletions that lead to the feather beta 
> keratin) to cause what would look like a global change to the entire 
> integument. 
> The scale pathway would continue, but scales would no longer form, and in 
> their 
> place we would have filaments. Natural selection could fine tune it from 
> there.
> 
> Going back from feathers to scales would be more difficult and might have 
> "required" a naked skin stage, but judging from what we currently know 
> about scale formation in birds, it too could have occurred as a couple of 
> mutations that ultimately ended up silencing feather formation on the cascade 
> that lead to integument development on the tarsometatarsus.
> 
> Jason
>