RE: Dromornithids and size limits.

["Jaime A. Headden" <qilongia@yahoo.com>]

Eric Martichuski (herewiss13@hotmail.com) wrote:

<Are these ground or arboreal birds?  Being able to use one foot while the
other is tightly gripping a tree branch isn't quite the same as
_balancing_ 
on one leg while using the other.>

  Don't really matter, but these are arboreal.

<Effectively, yes.  But are they _effective_ climbers?  Aren't most
tree-adapted quadrupeds likely to be faster, and more agile?  Plus, they
have their jaws free.  Can a parrot climb and hold a nut in its beak at
the same time?  Well, maybe it could, but it'd still be clumsy.>

  Why would these additional conditions or limits on motion matter? A
hoatzin exapted forelimbs to wings, so looses that. This doesn't make
flightless mammals better, since those mammals that do fly also have such
physical restrictiosn given their wings. This doesn't make mammals better.
AGAIN. I mean, I am sure I could tap on four typewriters at once if I
spent enough time learning to type with just my hands, then learn to type
with my toes, but that means diddlysquat to anything else. How about
bouncing up and down while balancing three bowling balls, juggling flaming
torches AND chainsaws, while singing the National Anthem? Additional
conditions to make mammals superior over birds aren't going to work. One
can find plenty of things birds are better at than mammals, and vice
versa. These are niche exaptations, and specializations, that come with
prices. To swim, pengiuns fly underwater and loose any effective asymmetry
in their feathers (an adaptation to function and environment) and become
HORRIBLE walkers, as are loons ... are these birds now suddenly worse for
the specialization because "mammals can do it all at the same time?" Which
they can't, I might add. Parrots are invariably better climbers than
sloths, much faster, and much more utile.

<Quite true.  But _how_much_better_ can they improve?>

  So far, without using sparrows, these birds have been equated with
Chimpanzee-level intelligence in their problem solving and tool use skills
for some species. That's a tad bit better than a mouse. Dolphin, without
any manipulatory anatomy whatsoever, have been given similar marks in
intelligence

<They certainly do.  All I'm saying is that a tetrapod is, all things
being equal, better poised to develop a _superior_ means.  Birds usual
maintain  their edge despite "inferior" adaptations precisely because of
their wings.  Lose flight and get stuck with the "inferior".  Some niches
_will_ remain open for obligate terrestrial birds, but they don't have the
evolutionary _pathways_ to explore as many niches as tetrapods...or at
least, not explore them as quickly and effectively as a tetrapod itself.>

  Whoa, please. Birds are tetrapods, too. They adapted for the sake of
loosing "hands." And still managed to do what they needed to do. No mammal
but bats fly. ALL birds were fliers then lost the ability for
specialization. This does not make them INFERIOR. Qualities, I might add,
of "inferior" and "superior" are antiquated Victorian ideals that the more
mammal-like or human-like something is, the BETTER it is, but this is
false. The ability to manipulate has not made oppossums suddenly superior
to their coevals, nor has it made the cane rat so much more superior than
to the cane toad, which eats it. There is extensive documentation of avian
intelligence, and perhaps one would be wiser to examine that hands do not
make for superiority.

<In their current niches, yes.  If a flightless bird _attempted_ to enter
the fossorial niche, all things being equal, it would find itself at a
great disadvantage against a tetrapod entering that niche
at_the_same_time.>

  Once again, birds ARE tetrapods. And your hypothesis would require
testing before you can make any conclusionary statement from it.
Otherwise, it's flat-out anecdotal and worthless in science.
 
<Because a generalized tetrapod is already a better excavator than a 
generalized biped.  If you're dealing with a flightless bird who's been so
for some time, so that the wings have atrophied to almost nothing (like 
kiwis), it's at an even _bigger_ disadvantage because bringing the wings
into play as shovels requires bringing them back as _limbs_ in the first
place.>

  What makes a gopher a better burrower than a burrowing owl? How about
what makes an ovenbird a better builder than a beaver? There will always
be better animals at doing things they are specialized for. I don't see
descriptions apart from what I write that is describing things birds are
better at than mammals, either.

<Meanwhile, while the Killer Bird has one predatory appendage, the 
sabretooth, or other predator has _three_.  A lion leaping up to claw and 
bite as the hindquarters of its fleeing prey has a better chance of
staying attached than a phorusrhacoid would with its single, albeit
wickedly hooked, anchor into the prey's flesh. _In_general_ a tetrapod
predator has an advantage over a biped predator.>

  A phorusrhacoid actually has three killing appendages in the smaller
forms, and becomes a running sword in the larger, but it's not like the
feet cannot hurt if used to kick or hold down struggling prey; in fact,
the secretary bird, a falconiform, uses it's feet primarily and is an
example of a "one-legged tool user while standing on the other foot" that
is also terrestrial, even if the tool its using IS it's foot and its
clobbering a snake to death while doing that. A cat, on the other hand,
typically does not kill with the paws, just the mouth. It uses the feet to
grapple with, but so do birds. It uses the jaws to strangle or rend, but
birds can do both with their feet and jaws. As if that matters, though.

  Anyways, this is turning into a modern versus 1800's argument of
superiority of mammals. A few facts:

  1. No mammal has successfully invaded a typically avian habitat, nor has
a bird, that we know of, have done the same to a mammalian habitat. This
does not mean that either is inferior to the other. Does an ostrich not
provide enough competition to prevent successful cheetah invasion into
northern Africa?

  2. Birds are tetrapods, as a tetrapod is not defined by having four
TERRESTRIAL limbs. Birds actually went through a likely four-legged
transition from bipedal to clambering to glider to flier, and retained and
sustained multiple locomotory modules, unlike mammals (bats, for an
example, have integrated the hindlimb INTO the wing and cannot utilize the
leg apart from the wing unless landing, somethign birds can do one better
by manipulating structures in the air given the separation of these
modules for walking and flying).

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


        
                
__________________________________
Do you Yahoo!?
Yahoo! Small Business $15K Web Design Giveaway 
http://promotions.yahoo.com/design_giveaway/