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FW: The ground-nowhere hypothesis on the origin of bird flight



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A proavian can not be working both against/for gravity at the
same time? Why not use the wings as spoilers to pin yourself
against the substrate while running up a tree thereby defying
gravity?
=20
Aerial locomotion could also be used to increase one's mass against
prey by using the wings as spoilers=3B to avoid prey biting back=3B
by dragging prey to keep it off balance=3B there may be multiple
reasons for this all working in unison.
=20
As a side note=2C catch the Mongolian Eagle Festival. There you'll
witness an eagle strike a deer from behind while the deer=20
sommersaults ass over end right on top of the eagle. The eagle=20
still comes up on top never once losing its grip. Scary dino.
--dale=20
=20

----------------------------------------
> Date: Thu=2C 8 Oct 2009 22:46:57 -0700
> From: tijawi@yahoo.com
> To: dinosaur@usc.edu
> CC: tijawi@yahoo.com
> Subject: Re: The ground-nowhere hypothesis on the origin of bird flight
>
> David Marjanovic wrote:
>
>
>> I keep reading on this list that the
>> ground-up/trees-down dichotomy is outdated. It is outdated
>> as a dichotomy -- the number of hypotheses is greater
>> than two. However=2C reality does not need to lie in the
>> middle. Probably it lies somewhere else entirely.
>
>
> That is true in an ecological sense. However=2C the old ground-up/trees-d=
own dichotomy boils down to the role of gravity in aerial behavior: Was the=
 pro-avian working with or against gravity? This is not really about whethe=
r the pro-avian lived in trees=2C or on the ground=2C because some models t=
hat favor a terrestrial pro-avian also propose a gravity-assisted path to f=
light - like 'Pouncing Proavis'.
>
>
> So in the sense of the role of gravity=2C there can only be two hypothese=
s: the pro-avian is either using gravity to its advantage (e.g.=2C Pouncing=
 Proavis=2C or an arboreal glider)=2C or it is actively fighting against gr=
avity (e.g.=2C leaping from the ground into the air to catch insects). At a=
ny given moment=2C the pro-avian can either be working with or against grav=
ity=2C not both.
>
>
> However=2C it is theoretically possible that the role of gravity changed =
at different stages in the evolution of flight. This is why the dichotomy i=
s outdated. Such a switch seems to be implied in the "stability flapping" m=
odel: initially the predator is using gravity to its advantage (to help pin=
 down prey)=2C but at some later evolutionary stage the theropod uses its w=
ings to launch itself into the air=2C against the force of gravity. If I un=
derstand the model correctly=2C that is. (If I'm woefully misunderstanding =
this model=2C I apologise.) I'm really looking forward to the papers. I par=
ticular look forward to this statement being elaborated upon: "Selection fo=
r more efficient stability flapping provides a viable selection pathway to =
true powered flight." How exactly? What selective advantage would aerial lo=
comotion be to a predator that wants to pin down terrestrial prey? I'll hap=
pily W4TPs...
>
>
>
> Cheers
>
> Tim
>
>
>                                         =0A=
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