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



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