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

[Michael Habib <mhabib5@jhmi.edu>]

> True enough. Yet O. (and ancestors) acquired flapping flight through a 
> gliding phase, apparently. The point was that the feasibility of an 
> incremental gliding-to-flapping transition in bats isn't hard to 
> understand when you consider that 'accidental' insect/bat encounters 
> would occur while gliding tree-to-tree. The probability of such 
> encounters occurring on any given glide at any given insect density 
> can be graphed, given reasonable assumptions about speed and length of 
> glide.

Yes, but food resources are likely not the limiting factor - all I was 
saying is that there are mechanical constraints regarding gliding to 
flapping transitions that make such acquisitions less likely than that 
might otherwise appear.  We cannot, at present, actually quantify those 
likelihood.  With only four origins of flight, we have no statistical 
power to determine what type of transition is most likely, and 
simulations require assumptions on ancestral states.

> I don't think an "incipiently flapping glider" could maintain a 
> lifestyle wherein "incipiently flapping" was advantageous, in the 
> presence of birds, due to competitive constraints. Therefore, the lack 
> of extant "incipiently flapping flyers" does not imply that the 
> 'mechanical hurdles of the passive-to-active transition are 
> insurmountable, or so difficult as to make "tree's-down" inherently 
> unlikely', implying that "ground-up" is more likely. That was the 
> assertion made, if you want to check the context by re-reading the 
> thread.

Actually, it wasn't the assertion made.  I merely pointed out that 
passive-to-active transitions may be rare for mechanical reasons - 
there is no way to quantify how rare, without having a specific 
ancestral state nailed down.  Passive-to-active transitions clearly can 
occur, since bats seem to have done so (although we're not sure about 
that), but it might require more specific starting conditions than 
generally realized.  And, with only four power flight origins in the 
first place, we will never really know how "rare" such a transition can 
be expected to be.  I suppose a simulation study might able to give a 
tentative answer for very specific starting conditions, but I'm not 
sure how much I'd trust those results.

> The gap between wing and body is a trivial matter, IMO.

It is not trivial, at least from the standpoint of fluid flow and 
flight.

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