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Before I continue, does anyone know if a 5 ounce Archaeopteryx could carry a 1
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> To: firstname.lastname@example.org
> CC: email@example.com
> Subject: Re:
> Date: Thu, 25 Sep 2008 04:30:00 -0600
> comments inserted.
> ----- Original Message -----
> From: "Sim Koning"
> Sent: Wednesday, September 24, 2008 11:54 PM
>> These are the problems I'm having with the ground up hypothesis; assuming
>> that protobirds already had elongated feathers on their arms, what
>> advantage would this give a ground running predator?
> Increased mobility.
If early wing feathers gave some significant advantage to a cursorial animal's
mobility, then why have almost all Struthioniformes and Phorusrhacids (which
were predators) evolved extremely vestigal wings that lack flight feathers.
Some species actually have wings so small that they are not even visable.
Orstriches have large wings (relatively speaking), but they have completely
lost their flight feathers, which have been replaced with soft downy insulatory
feathers that they also use for display.
>> If they leapt into the air, these "wings" would actually slow them down
>> due to drag,
> It is just as likely that the 'wings' would not slow them -- due to reduced
> form drag resulting from feathers 'reshaping' the area behind the arm
> (thereby allowing the arm to be moved away from the body during running
> without substantial penalty and with some advantages).
Drag by definition is resistance to an object moving through fluid, which must
be overcome by thrust which in turn (in the case of a wing) produces lift: so
basically it would slow them down if they extended their wings. This would
explain why many flightless birds have completely lost their flight feathers
and have extremely reduced wings.
>> making them more vulnerable to predators.
> Or perhaps -- making them less vulnerable to predators.
>> I think a more streamlined animal with powerful legs and no "wings" at all
>> would make more sense for a specialized "jumper" (kangaroo).
> Why presume that the early wings make them less streamlined when jumping?
Would you race a motorcycle while wearing a cape? I imagine it would have a
similar effect If the earliest forms had simple elongated protofeathers, or
even primitive flight feathers for that matter. Yes a simple wing could extend
their jump, but it would also slow them down due to drag
>> Also, why would they be leaping up into the air in the first place? To
>> catch insects? No animal that does this exists.
> Cats do it.
true, good point.
>> If they evolved simple wings to provide lift while running,
> Why would they do that? More likely that the early wings would act to
> increase mobility rather than lift. The increasing ability to produce lift
> would be initially secondary.
>> wouldn't this actually reduce traction
> Yes, which is possibly why the wings could be oriented to modulate or
> increase traction rather than reduce it.
Why haven't flightless birds kept this feature? The only birds that do this, do
it to run up trees and then jump out of them.
>> and in turn slow them down and make them less stable?
> Wouldn't necessarily slow them down, and the ability to selectively modulate
> stability is an advantage rather than a disadvantage.
If they leapt into the air, they would rapidly decelerate, making them unstable.
>> To me, an at least somewhat arboreal animal that used it's elongated
>> feathers or even leapt to parachute from an elevated position
>> makes more sense;
> Since many improvements in parachuting and/or gliding ability don't lead
> toward the direction of powered flight, doesn't that create problems for
> your scenario?
How do you know this? If a gliding rodent begain evolving extended webbed
fingers it could gradually lead to the same condition seen in bats. Sometimes
the only difference between a gliding aircraft and an airplane is one has
thrust, one does not; otherwise the wing design is largely the same. In fact
some gliders have engines that are used occasionally. A highly efficient
gliding animal could probably reach a state of sustained flight by simply using
the wind; from that point it would only need to develope way of producing
>>Primitive bats had greatly elongated fingers with claws on all five digits
>>which they used for climbing as well.
> What is the evidence for this presumption?
The little guy actually kinda reminds me of Archaeopterx, with all the highly
elogated clawed fingers and relativlely long hind limbs and tail.
>> Fossil bats make a good case for at least one group of flying animals
>> evolving from arboreal gliders.
> In what way do they make that case?
See above. I have a hard time imagining that thing running along the ground
with any great speed.
>> There is a strong selective advantage for an arboreal animal to evolve
>> some sort of parachute or gliding system to prevent injury from falling or
>> to conserve energy by leaping from tree to tree instead climbing all the
>> way down and back up a tree trunk, or cliff face: this is made obvious by
>> the large number of arboreal creatures that have evolved in this way.
> This is quite true. How many of them seem to be developing the ability for
> powered flight?
How many apes seem to be developing sapience?
>> On the other hand, you do not see any primarily ground running, leaping
>> animals evolving some sort of simple gliding or flight system; the only
>> animals that do anything like this are birds,
> And flying fish, and hatchetfish (which also flap while aloft).
Which jump out of water to escape predatory fish. What are these protobirds
doing, jumping up to a convenient biting hight for a 10 foot tall theropod? If
they are jumping to catch prey, the immediate drop in velocity due to drag
would cancel out any benefit for a cursorial predator. In my *opinion*
predators whith very small wings and poweful hind legs would be more effective
as leaping predators.
>>yet they already have a fully developed and highly sophisticated flight
>>mechanism. There are plenty of jumping, kangaroo like animals, yet none of
>>them have evolved wing membranes or any organ other than stronger legs (and
>>smaller arms) to increase airtime.
> Which demonstrates that there is more than one way to skin a cat. A good
> place to mention that the ground up vs. trees down scenario is a perfect
> example of a potentially false dichotomy.
- From: "Richard W. Travsky" <firstname.lastname@example.org>
- From: jrc <email@example.com>