[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)



--- On Fri, 9/26/08, Mike Habib <habib@jhmi.edu> wrote:

> It could just as easily be support for the hypothesis that
> gliding to  
> powered transitions are very rare for mechanical reasons,
> though.  

Not really. Competitive exclusion is a basic principle, while postulating that 
mechanical hurdles prevent a passive-to-powered flight transition are not, 
especially when it is consensus that bats and pterosaurs did it. 

Heh. Although I gather there is a contingent that favors a terrestrial origin 
for ptero's. Sorry, that was a cheap shot. Anything (almost) is possible.

> You  
> could be right on the money, but it just seems like such a
> strong  
> blanket statement that it makes me slightly skeptical.

It was a comment made in rebuttal of the assertion that our current lack of 
'gliders flapping feebly' supports the idea that powered flight evolved w/out a 
preliminary gliding phase. 

> >> but birds and bats certainly both appeared in the
> presence of pre- 
> >> existing powered flyers.
> >
> > I think it is a safe assumption that they were not
> faced w/ the  
> > competitive barriers modern-day putative transitionals
> would have to  
> > overcome, from the perspective of niche
> specialization.
> 
> Why is that?  There was certainly specialist ecologies
> among flyers in  
> the Mesozoic, and it's not clear how much specialist
> ecologies impact  
> competitive exclusion.  One could make the argument that it
> is  
> actually "generalist" feeding modes, etc that
> would be more likely to  
> produce exclusion.  

I note that incipient birds did not have to compete w/ either modern birds, or 
bats. Or (I assume) mice, shrews, weasels....

> > Of course, pure gliders are MUCH more numerous than
> incipient  
> > "ground-up" animals.
> 
> Yes, this is true (at least in the modern time slice).  So
> we have two  
> different types of rarity - terrestrial origins for flight
> are  
> probably rare because heavy exaption is involved (i.e.
> rarity by  
> ancestor constraints).  

Heh. Oh, do you have an example of "terrestrial origins for flight"? :D

More seriously, "ancestor constraints" are what I call "pre-conditions", and 
they require lots of evolution to fulfill. And seem to be rare in themselves.

> Arboreal origins of powered flight
> are rare  
> most likely because transitions to powered flight from an
> obligate  
> gliding morphology are rare (i.e. rarity by mechanical
> transition).   

But "known" to have occurred; quote marks inserted because anything is possible.

Don