RE: Compiled theories of flight's origin

[Tim Williams <twilliams_alpha@hotmail.com>]

Anthony Docimo wrote:

> * Ground Up - a ground-dwelling maniraptor flaps arms covered in 
> protofeathers, and after a thousand or so

> generations, it gets off the ground an appreciable amount.
>
> * Trees Down - a tree-dwelling maniraptor spreads its protofeathered arms to 
> slow its leap from the branches

> to the ground/prey.



Traditionally, most scenarios concerning the origin of vertebrate flight have 
fallen into these broad categories ("Ground Up" or "Trees Down".  However, this 
can be potentially misleading.


Firstly, the "Ground Up" vs "Trees Down" dichotomy focuses on the role of 
gravity in the incipient stages - if the animal is working with it or against 
it.  The former is usually associated with an arboreal ecology and the latter 
is usually associated with a terrestrial ecology.  But there are exceptions.  
For example, the "Pouncing Proavis" model proposes that pro-avians leaped 
downward, but were not arboreal (they launched themselves from rocks, etc).  On 
the other hand, somebody (might have been GSP) suggested that pro-avians lived 
in trees, but leaped upward from branch to branch ("Trees Up").


Secondly, there is no reason to assume that the "Ground Up" vs "Trees Down" 
scenarios are mutually exclusive.  Both behaviors may have played a role in the 
incipient stages of flight.  I supect this is especially relevant to the origin 
of avian flight; but probably not for the evolution of bat flight.  Dunno about 
pterosaurs.


Thirdly, it helps to remember that for the evolution of powered flight, the 
development of the flight stroke is equally important as the development of the 
wing.  Many hypothetical pre-flight scenarios focus on one and neglect the 
other - irrespective of whether they fall into the Ground Up" or "Trees Down" 
categories.



Cheers

Tim
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