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Re: bauplan convergence



I think there is a bit of a conceptual problem both
here, and with some of the others posts re this
thread.

For whatever reason it appears that feathers had a
potential second role vis a vis flight that hair
lacks. The lack of branching filaments on hair strikes
me as one obvious difference that could account for
this, meaning that the role of hair is actually more
limited than that of feathers. I can see how a simple
feather evolved for insulation could then evolve into
a flight feather, but not a hair - hence no flying
lemurs and indeed no flying mammals that use modified
hairs for this purpose.

Jaguars and things like that don't seem to be really
appropriate points of comparison.

As well, surely it is a mistake to assume that
evolution proceeds logically. We are trying to
understand what happened within a particular lineage
and its CONTINGENT adaptations to survival. And
probably just one particular sub-lineage within the
main one.

Other lineages, even if their circumstances are
superficially similar, will in all likelihood take
divergent paths, the only criterion being survival.

The acquisition of simple feathers did not mean more
complex structures were inevitable. There does seem to
be an aspect of serendipity in these matters.

Perhaps Caudipteryx gives us something to speculate
with, imagining a small theropod that didn't have
wings but enough complex feathers on its arms to at
least be able to glide.

Garth

--- Rob Gay <rob_redwing@hotmail.com> wrote:
> >From: "Ahmed al-Mahasa Sha'ad"
> <am_shaad@hotmail.com>
> >If this happend in origin of birds it does NOT mean
> it MUST happen in every
> >linage of tree-living predators.
> 
> So the question is, what drove this to happen in
> birds and not in the other 
> tree-dwelling predators? What sort of circumstances,
> that are not present 
> today, would make therapod dinosaurs fly? Many of
> the animals that live in 
> trees today, or at least have some history of
> climbing trees, have fur, 
> which could be adapted over the course of time, to
> become something like 
> feathers. (Interestingly enough, the only flying
> mammal, the bat, uses skin 
> flaps and not modified hair). So far, however, this
> hasn't happened. I see 
> the evolution of hair into feathers to be much
> easier than the evolution of 
> scales into feathers. So, if we have a population of
> small therapod 
> dinosaurs living in the trees, fulfilling the role
> of, say, lemurs, why did 
> the dinosaurs start to fly, and why haven't lemurs
> taken wing?
>
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