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Re: flapping from gliding
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
> 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.
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 ]
John C. McLoughlin