Re: flapping from gliding

[JCMcL <darwincr@laplaza.org>]

On Wed, 25 Sep 1996, Bonnie Blackwell, x 3332 wrote:

> Ron Orenstein asked why gliders might develop flapping, and decided that
> the only option was to get to things above them.  let me offer one more
> idea:
> Say you have a glider who evolves in a forest with lots of trees (as most
> seem to do).  When you glide you have no worries about getting to another
> tree - as long as the tree density remains stable.  Let's say that
> environmental change (drying, increasing seasonality, temperature change
> or even new species that use fire for germination like the Eucalypts
> leading to more fires) causes a decrease in tree density.  If you want
> to continue to glide, you better increase your accuracy if you want to
> be sure to land in a tree rather than becoming a messy schplatt on the ground.
> 
> please no flames, this was merely a top of the head thought at too early
> an hour.
> b

I wonder at the absence of speculation on braking and turning.  Assuming 
that proto-birds were light theropods, perhaps insect-eaters (a broad 
assumption, but one with which I've always been comfortable), and that 
larger cousins preyed upon these light theropods, and that all of the 
animals in this short food chain were swift and agile and possessed of 
comparatively low body mass, I have always guessed that a little 
(Archaeopteryx-sized) theropod that could brake suddenly by pumping 
feathered forelimbs forward and use these forelimbs' configuration to 
change direction rapidly, would perhaps more frequently escape their 
perhaps swifter but less agile (because of greater mass) relatives.  

        This scenario of course presumes that birds evolved from fast light 
ground-runners rather than from some sort of arboreal form, like a 
feathery analogue of colugos ("flying lemurs").  

        It does seem to me that in a world of fast light predators, the ability 
to stop and turn on the Mesozoic version of a dime would confer 
considerable selective advantage.  

[We actually had this discussion here on the list last December (LN
 Jeff started it with a reference to running chickens).  You might
 want to check the archives.  I know it's not unusual for us to
 revisit topics here, but this particular topic stands out in my head
 because I never felt George understood my reasoning as to why
 feathered arms could have been advantageous to a non-volant cursorial
 theropod.  I'm glad someone else sees it...  -- MR ]

Many thanks.  

John C. McLoughlin