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Re: bauplan convergence



Bats and pterosaurs both developed flapping flight via wing membranes.  

It is generally agreed though that bats and pterosaurs are not as strong
flyers as birds are.

Birds seem to have managed flight without ever depending on skin
membranes.  Ergo they had something else as the equivalent ALREADY in
place.

Thus we have further evidence that birds had feathers before they were
even trying to fly. 

And I might suggest that proto-birds didn't pass through a stage of
exclusive gliding as proto-pterosaurs and proto-bats probably did,
before those two groups developed flapping ability, because birds
weren't membrane-dependant.

-Betty Cunningham

Garth Godsman wrote:
> 
> 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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-- 
Flying Goat Graphics
http://www.flyinggoat.com
(Society of Vertebrate Paleontology member)
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