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Running with arms out



--Orig. Message:-- From: Betty Cunningham <bettyc@flyinggoat.com>
Date: Fri, 07 May 1999 14:42:36 -0700

>If it was being chased by a roughly equal sized predator, I'd see it
turning around and spreading it's arms as wide as possible in order to
look as BIG AS POSSIBLE.  Maybe even hop up and down and make rattling
noises as it flapped and looked as fierce as possible.
<

I agree that trying to look as big as possible is often used to deter
attack, and when trying to intimidate (as someone said with geese).

However, that is when you are still trying to instill fear.  When you are
running away as fast as you can and your predator is chasing you, it is
clear to it, to yourself, and to any third parties, that though the predator
might just harbour some last modicum of fear, salvation in that direction is
pretty remote.  Better options are:

1)  Show the predator that you're incredibly good at running away, in the
hope that it'll give up chasing you and go after your neighbour or just give
up altogether;

2)  Attract the attention of other predators in the hope that they will
fight yours and you'll be able to crawl away in the confusion;

3)  Attract the attention of colleagues who will help you;

4)  Flee as fast as you can.


Sticking out long arms with claws and feathers on wouldn't really satisfy 1,
and surely not very much 2 & 3; however, it would hamper 4 in terms of
snagging, and in the earliest stages of wings before lift/thrust had
evolved, in terms of drag.  Using drag differentially on one side only would
theoretically give some benefit to manoeuvrability, though I don't like the
idea.  I hope eventually to come up with some convincing specific reasons
other than that if drag was working in this way it would would a whole lot
better in the falling situation.



In Tom Holtz's reply to Larry Febo: Date: Fri, 7 May 1999 17:55:57 -0400
(EDT):

>Consider this scenario.  I'm not saying it is correct, but I am offering it
as a possibility:
I) Ancestral dinosaurian carnivores with moderate length arms, wrists
without much "folding" ability in the manner of birds.
II) Selection favors variants with a longer reach (longer arms, longer
hands).
III)  Selection favors variants among long-armed dinosaurs with the best
ability to fold and tuck the arms.
IV)  Having evolved the fold-and-tuck structures, variants with greatly
elongated arms can develop and still use their forelimbs to sieze prey or to
climb with, without the arms getting in the way while running.

Although this is all a just-so story, it matches the pattern we see in
theropod evolution (I being basal theropods and ceratosaurs, II being basal
tetanurines, III being basal avetheropods (with small semilunate carpal
block) such as carnosaurs, _Coelurus_, _Scipionyx_, tyrannosaurids, and
maybe ancestral ornithomimosaurs, and IV being long-armed maniraptorans.
<

I would agree with that as a possible scenario but with two reservations:

Is a gradual lengthening of arms really there?  (This is a delicate point
because in any theory there has to be a lengthening of the arms, but Larry's
(and my, Larry!) position  advocates an explosive initial lengthening for
flight purposes; however, there might also be a lengthening for
tree-climbing purposes.  In this case, we might expect any lengthening to be
associated more with the smaller specimens, as is I believe the trend.)

Why did this new way of doing an old trick only appear after 100 mys?


Also, in reply to a posting by Dan Pigdon, Tom says:

Date: Fri, 7 May 1999 18:01:29 -0400 (EDT)

>>At 12:36 PM 5/7/99 +1000, Dann Pigdon wrote:
>I'd have thought that the last thing you'd want to do if being
>pursued by a predator would be to stick your arms out. Wouldn't this
>actually slow you down?

>So I would have thought, and so did most people, which is why a lot of
folks
thought that it was biomechanically unfeasiable.  The point of the paper in
question is to show that, contrary to expectations, a running
_Archaeopteryx_ or other primitive protobird flapping its wings actually
adds thrust, and thus becomes faster.  Goofy sounding, but that's what their
model shows.  Find a flaw in their model, and get your paper published as a
Correction!<

Simply sticking your arms out remains unfeasible.  The paper demonstrated
that the forelimbs of a running bird such as _Ax_ could contribute both lift
and thrust (which is not the slightest bit worthy of space in "Nature"), and
this might help it run faster (which it *didn't* demonstrate, but wouldn't
be very surprising at all to most people and was not to my mind worthy of
publication anywhere).

One flaw is in begging the question by seeing if the finished product could
do the job, when we want to know how the earliest versions might have coped;
however no correction of this is possible because the other flaw is not in
their model but in the system which allows "Famous Experts" space to print
that kind of thing, but denies bandwidth to others with more significant
news.


>From another part of Tom and Larry's discussion:

Larry made a very good point:

[LF:]>>Theropods may have been fast enough for takeoff flight from the
ground, but
>there are other factors involved. Flight feathers (for one), which to me
are
>extremely specialized structures, and flapping motion, which if restricted
>to such would seem to be an unlikely "pre-adaptation" to have developed for
>the future use in flying. These two items alone seem better explained as
>holdovers from a previously specialized function of actual flight rather
>than being of significant use to a non-flight -capable organism in it`s
>forays on the ground.<

[TRH:]>Unless you are suggesting that remiges ("flight feathers" [...]) and
flapping motion had some previous other use (gliding,
parachuting, etc.), you are playing in the game of magic.  That is: this
novel structure can only be used for this purpose, therefore it has always
been used for this purpose.  However, barring magic or genetic tampering,
novel structures had some morphological precursor, which may indeed have had
a different use.<

[This is JJ now, live (from So'ton)(snip this bit out in any later
quotes!):] Larry's point on the extraordinary detail of flight feathers
could be considered partly one of parsimony: why look for two reasons for
such a specialised feature to evolve when one would do.  (Of course, in the
conventional theory it didn't evolved twice - just once for some unknown
reason, followed by exaption for flight).

However, the other aspect for which I don't have a generic name is: isn't it
an astounding coincidence that such a detailed form would have been so
amazingly perfect for flight?  Also, if it turns out that feathered dinos
were rather successful presumably this unknown useage of flight feathers
would have conferred some advantage of real value.  Why is it we don't have
a really convincing demonstration today of this "original" use?



<gejd@concentric.net>  said:  (Date: Sat, 08 May 1999 10:24:43 -0400 )

>Questions: I don't have any ostrich movies handy to look at. Do ratite
birds flap their wings when they run?<

I've a feeling I heard a discussion a few years ago where someone said rheas
used their wings for maneouvring, but they didn't say ostriches did.

I would also like to draw people's attention to the fact that tree and
cliff-fledging ducklings and goslings flap their little wing stubs for all
they're worth when they leap out of the nest.  Not really because it's
particularly relevant, but more because it's a charming symbol of endeavour
and optimism I'd like to share with you!  However, if we did seek
evolutionary benefits for what might seem to be a waste of energy, we might
say that this increases drag (and therefore enhances survivability - some
chicks must surely get injured in these falls) in two ways:

1)  If you're flapping your wings, your wings must be stretched out in the
first place.  If a well-defined behaviour (such as flapping) is "waiting in
the wings" for triggering in fairly similar circumstances, and it has a
useful spin-off (drag increase caused by stretched-out wings), it's
invocation is surely not a particularly unlikely course for evolution to
take.

2)  Wings flapping in an up-and-down sense, even in a vertical free-fall,
increase drag compared to stationary extended wings.  Admittedly when the
wings are flapping upwards, they decrease drag.  However, when the wings are
flapping down, they increase it, and as the drag depends on the square of
the speed through the air, the gain when flapping the wings down outweighs
the loss when moving them up.


JJ