RE: The new Archaeopteryx from... Wyoming?

[Jeff Hecht <jeff@jeffhecht.com>]

At 8:52 AM -0500 12/2/05, Thomas R. Holtz, Jr. wrote:
>>  Perhaps powered flight was
>> acquired (and lost) multiple times within Paraves.
>
>Perhaps. Or (as I have argued before), perhaps actual powered flight is 
>limited to Pygostylia or even a more restricted clade
>(Ornithothoraces perhaps?), and small members of the other paravian branches 
>had limited aerodynamic ability (WAIR, gliding, etc.)
>rather than actual powered flight.

Perhaps we're also going to have to develop a more precise definition of 
"actual powered flight." 

Flight must have developed in a series of stages, such as wing-assisted incline 
running. Each one must have had some value to the organism. The little 
dino-birds that escaped predators by flapping their arms as they climbed might 
have next evolved wings with enough lift to help them flutter down. Then they 
may have flapped those slightly bigger wings enough to lift them up into a 
shrub that was hard to climb using wing-assisted incline running. The next step 
would be flapping over to the next shrub, or flapping up to a higher branch on 
a nearby tree when confronted by a predator big enough to reach them in the 
shrub. Is "powered flight" the ability to flap wings enough to get to a branch 
otherwise just out of reach, or does it require the ability to fly a certain 
distance or for a certain time? 

Flight has such clear advantages that there may have been multiple detailed 
paths to flight within dino-birds who were already part-way there. Some may 
have gone through a gliding stage, some may have evolved tree-climbing 
capabilities so they could navigate the trees more effectively once they got 
there. 

THey also may have traded off powered flight for other advantages, such as 
size, or tree-climbing capability if that compromised the musculature and 
skeletal structures needed for fully powered flight. So in that larger scheme 
of things, it makes sense that many clades may have gone back and forth across 
some definitions of "flight." 

-- 
Jeff Hecht, science & technology writer
jeff@jeffhecht.com
Boston Correspondent: New Scientist magazine
Contributing Editor: Laser Focus World
525 Auburn St., Auburndale, MA 02466 USA
v. 617-965-3834; fax 617-332-4760