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Re: Dinosaur Revolution Review



Jura <pristichampsus@yahoo.com> wrote:

> 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.


I hadn't heard this weight reduction hypothesis for scales - although
I have heard it cited in the past for the loss of teeth in birds,
where it seems equally implausible.


It is likely that the loss of a body covering of scales preceded
flight in maniraptoran evolution.  This is just a guess, but it might
have something to do with miniaturization - in other words, reduction
in body size in the line leading to birds.  If feathers served a
purpose in insulation, then scales might have impeded this function in
highly active critters that had high surface-area-to-volume-ratios,
and needed to lock down as much body heat as they could.  Also, there
is the physical constraint of having both scales and feathers
distributed over the body in animals that weren't very big to begin
with.  At some point, scales might simply have become expendable.


Anthony Docimo <keenir@hotmail.com> wrote:

>  Some might argue that that is what birds can afford to do, after they first 
> got good at flying around.


Confuciusornithids seem to have been poor fliers - and yet they had
elaborate, non-aerodynamic tail feathers that would have been an
outright hindrance to flight.  _Epidexipteryx_ and _Caudipteryx_ had
feathers that were used solely for display (different kinds of
feathers), so this habit of using feathers solely for ornamentation
was retained in aerial taxa such as _Confuciusornis_, no matter what
the aerodynamic cost.





Cheers

Tim