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



It (gliding+flapping) is only viable if there are no flappers around that can glide whenever they want to.

Why not? Yes, clearly competitive exclusion can be powerful, but do we really expect that the simple existence of powered flyers should completely shut down gliders with limited powered ability? It's a reasonable hypothesis, and a very interesting one, but I don't think we can frame it as a conclusion at this stage.


And if so, then that would seem to argue against a gliding stage in almost every group of flyers - only insects evolved flight in the absence of other flying animals. We might argue that pterosaurs had sufficiently small overlap in body size with insects that they did the same, but birds and bats certainly both appeared in the presence of pre-existing powered flyers. I suspect that the competitive influences are more complicated than a simple, blanket exclusion.

Yes, but there is nothing to eat there now, which is why it is empty...

But many of the pure gliders alive today compete for food with powered flyers, as it is. I'm a bit uncertain as to why competitions coefficients should be higher (in terms of food overlap) in the case of incipient flapping. Incidentally, all of the living obligate gliding taxa have planforms and/or airfoil structures that would lose efficiency to a flapping stroke.


Quite correct. Acquiring prey by gliding simply isn't going to work when birds are around, but commuting is always an open option if you have a job to go to...

But animals like Draco and Chrysopelea apparently do chase prey using gliding, in some cases - though it's not aerial hawking - they pounce upon prey on a distant branch or tree. Of course, most birds don't hunt by aerial hawking, either.


So I continue to maintain that the obvious "terrestrial-ness" of Archaeopteryx, et al, is not necessarily key to the gravity vs muscle power debate.

That may be true. I'm not sure I'd frame a separation between gravity and muscle power usage, however. Even in those groups where arboreal stages have been critical to the origin of flight, it is quite likely that powered leaps were involved - there is no reason to assume that flight evolution needs to be begin with simple falls (especially for a group such as birds, which inherited a strong leaping apparatus). This is yet another reason why setting a threshold between arboreal and terrestrial origins is difficult and misleading - both may actually involve very similar launch dynamics.


Also, the debate IS a dichotomy in the sense that you HAVE to start somewhere. Once the ball is rolling, the dichotomy disappears, but that first step is is a booger...

Granted, but if the evolution of powered flight in a given group involves movement between the ground and trees, or involves an intense mosaic of both arboreal and terrestrial forms, then we will probably never have the resolution required to pin down the ecology of the "first" ancestor in the sequence. And besides, if that "first step" happens to be populations that use both trees and ground running, then the dichotomy is really broken.


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