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Re: Dinosaur Revolution Review



Jura <pristichampsus@yahoo.com> wrote:


> I'm also hesitant to use (relatively) highly derived birds as examples that 
> scales and feathers can "live in harmony." I think these particular birds 
> (well, really just the owls) would make for a fascinating
> developmental study, and that results from that study would go a long way to 
> determining just how easy, or hard it is for feathers to revert back to 
> scales.


This assumes that feathers evolved directly from scales (a la Bock,
1965).  But it's my understanding that feathers are evolutionary
novelties (e.g., see Prum & Brush, 2002. Quart. Rev. Biol. 77:261-295;
Prum, 2005, In: Briggs [Ed.]  Evolving Form and Function: Fossils and
Development. pp 245-256.)  Scales and feathers are related, but not in
an ancestor-descendent way.


> I strongly suspect that this is an apomorphic
> trait for the owls, but without a good molecular study one really can't say 
> much either way.


This trait may well be an apomorphic trait of owls and other birds
that have 'feathery' feet (ptarmigans, some eagles, etc).  However, it
nonetheless demonstrates that feathers and scales can co-exist,
side-by-side.  The condition in owls &c need not be a reversion to the
ancestral condition in order to demonstrate the principal that it
could have occurred symplesiomorphically in Mesozoic theropods.


> Given this lack of integument change with ontogeny I find it highly doubtful 
> that a tyrannosaur hatchling would start off downy and then move to scales as 
> it matured.


Not necessarily - if the natal feathers co-existed with scales in the
hatchling.  No naked-ness is required, at any stage.





Cheers

Tim