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

[Michael Habib <mhabib5@jhmi.edu>]

don ohmes wrote:
> 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.

Competitive exclusion is indeed a well-established concept in biology, 
but so is the knowledge of mechanical constraints.  Besides, being a 
"basic principle" does not make a given factor more likely.  
Competitive exclusion is notoriously difficult to demonstrate, in fact, 
and it is still uncertain how important it is in determining 
evolutionary patterns.  Personally, I tend to think that exclusion 
plays a major role in many cases, but that doesn't mean that it gains 
"throw away" dominance over other explanations - especially when there 
are other constraints known to be a factor.  The mechanical hurdles to 
which I refer are not mere postulates, incidentally - the specific 
structure and planform of many living gliders is such that rapid 
oscillations of the airfoils would have a negative impact on vorticity.

The origin of flight in pterosaurs is currently equivocal.  The 
transition is a bit better supported for bats, but the details are 
still unknown - it is quite probable (given the morphological evidence) 
that a glide-to-powered transition occurred in bats, but we can also 
hypothesize that something about bat ancestors made this transition 
more mechanically feasible than it would be for many living groups of 
gliders.  We won't know until better fossil resolution is obtained from 
near the base of bats.

> 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.

No worries.  Actually, I consider the origin for pterosaurs to be 
currently equivocal, as do most pterosaur workers.  It is completely 
plausible that arboreality could have been involved - but it didn't 
have to be.

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

They may have had competition from pterosaurs, however (in terms of 
flying groups), and there were certainly plenty of small endotherms 
around.  There were no mice or weasels, but there were multis and basal 
therians.  Depending on the specific habitats and diets of the basal 
birds, they could have had numerous potential competitors.  The impact 
on flight evolution is currently difficult to determine.

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

As mentioned before, birds may very well be an example.  Insects might 
be, as well.  Pterosaurs are currently equivocal.

Cheers,

--Mike


Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181
habib@jhmi.edu