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Re: Do we have dromaeosaurid evolution backward?
I may misunderstand the principles behind WAIR, but a lot of arguments
I've read here and elsewhere in support of it as a precursor to flight
strike me as circular. In all the literature and videos I've seen
concerning how WAIR works, a complete upstroke appears to be
necessary. The same people who support WAIR as a precursor to flight
often do so because of data showing that basal paravians were
incapable of elevating the humerus above the horizontal (the same
degree of motion required by WAIR). It seems that if this really was a
limitation in basal paravians, WAIR is just as implausible as powered
flight. What am I missing?
Also, note that some modern ratites are highly cursorial and yet lost
not only asymmetrical remiges, but vaned feathers, and apparently this
happened several times. Recently flightless birds like the Kakapo
(which retains gliding/parachuting behavior) also has reduced the
asymmetry of its remiges. The fact that asymmetry is quickly lost
along with powered flight seems to argue against the idea that it is
aerodynamically beneficial in cursorial or parachuting forms.
On Thu, Aug 25, 2011 at 1:58 AM, Jaime Headden <firstname.lastname@example.org> wrote:
> Those then become exaptations. It may progress from a brooding "wing,"
> running aerofoils, WAIR aerofoils, parachuting -> gliding aerofoils, which
> would then force the wing to develop "braking" mechanisms such as the alula
> to assist in retarding stall. Wing planform control can exist very early on
> in the evolution of the structure, and need not ever involve the development
> of flight.
> Jaime A. Headden
> The Bite Stuff (site v2)
> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
> "Ever since man first left his cave and met a stranger with a
> different language and a new way of looking at things, the human race
> has had a dream: to kill him, so we don't have to learn his language or
> his new way of looking at things." --- Zapp Brannigan (Beast With a Billion
>> Date: Thu, 25 Aug 2011 15:28:23 +1000
>> From: email@example.com
>> To: firstname.lastname@example.org
>> Subject: Re: Do we have dromaeosaurid evolution backward?
>> David Marjanovic <email@example.com> wrote:
>> >> As I see it, one major problem with this idea is that if large,
>> >> pennaceous feathers originally evolved for aerodynamic purposes,
>> >> these feathers are unlikely to have arisen in "large" (2-4m long)
>> >> theropods that used their forelimbs for catching prey.
>> > I suppose that's where Hopp & Orsen (1998) come in.
>> Using the forelimbs to help incubate eggs might explain the presence
>> of big pennaceous feathers. But it doesn't explain why those feathers
>> would be aerodynamic. Or else, this step (bipinnate, aerodynamic
>> vanes) arose at least twice.