RE: Dromornithids and size limits.

["Eric Martichuski" <herewiss13@hotmail.com>]

> From: "Jaime A. Headden" <qilongia@yahoo.com>
>
>   Just would like to point out that as effective mechanics go and biology,
> birds do, in fact, have forelimbs. They are just wings. Manipulatory
> appendages in birds are mouths and feet, the former a more effective
> manipulatory tool than most mammals can achieve. Only among primates and
> smaller carnivorans/"insectivorans" or metatherians do manipulatory manus
> anatomy evolve, it is not so universal.

::smacks forehead::

And thus is illustrated the danger of imprecise writing.  Yes, birds have 
forelimbs. ;-)  However, once a bird gives up the "flight niche" for 
whatever reason, those wings become almost useless.  Penguins managed to 
turn them into flippers, but ostritches, emus, rheas, cassowaries, kiwis, 
dodos and other purely terrestrial birds have pretty much written off two of 
four apendages.

You will note that none of the birds I've mentioned are known for their 
manual dexterity (so to speak).  If you can't anchor yourself to a limb, 
it's rather awkward to stand on one leg while using the other to fiddle with 
something.  Any task best suited to _two limbs_ (even if they are 
undexterous) gets really tricky.

Now these species  _are_ well adapted for their environments, obviously, but 
I believe it would be much tougher for an effectively two-limbed bird to 
explore other niches than it would be for a quadraped with two  limbs 
_potentially_ free for adaptation (even semi-free works).

A degenerate wing will not easily turn into a clawed prey grasping limb 
(i.e. cats), a limb for becoming arboreal again (i.e. squirrels, primates, 
prosimians, etc. etc.), a general manipulator (i.e. racoons, beavers, etc. 
as mentioned above) or a burrowing limb (i.e. gophers, moles, prarie dogs).

While many birds do scratch out burrows or hollows, they don't fill any 
exclusively (or even semi-exclusively) subterranean niches.  Any attempt for 
them to do so would likely fail because they cannot specialize for the task 
as well as a burrowing mammal.

Birds do great things with their beaks and feet, but they're allowed to do 
so because of their wings, which give them a dimension none of their 
companion species can explore.  If, as we're postulating here, a bird 
species gives _up_ it's wings, then all you're left with is a maimed 
quadraped with some atrophied flappers.

To repeat: While I'm not saying birds could not adapt to fill the niches 
I've mentioned.  I _am_ saying they would do so less efficiently, and thus 
are more likely to be excluded by metatherians (or reptiles, whatever) 
through competition.

...and I think I've forgotten the original point I was responding to. ;-)

Does this all seem like an accurate statement?

Eric
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"There is no other wisdom,
And no other hope for us
But that we grow wise. -- Diane Duane
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