Reply to Scanlon (was RE: Archaeopteryx not...)

[don ohmes <d_ohmes@yahoo.com>]

Actually, my third eye was damaged when I was but a
youth; the result of a landing gear malfunction on the
astral plane... so I don't see a lot of details. Just
kidding about everything but not seeing details, of
course.

Your plotline seems entirely reasonable to me, if a
little specific. As evolution is a game of
probability, I personally prefer more generic starting
scenarios, allowing for lots of radiation into various
specialized niches, including ones such as you
describe. We seem to be in agreement as to the
potential importance of camoflage for elicting
protofeathers in places and forms unexpected for
insulation function. Doesn't eliminate display, etc.

As long as we are sharing "visions" of flight
evolution, I'll discuss what I consider to  be my two
main observation-based insights, such as they are. 

"Just So Stories"-- ]:0 

1. I once observed an alligator (~2m) moving in high
gear across a wide flat-bottomed ditch that was
overlain w/ a few cm of water and aquatic weeds. It's
front legs were well clear of the ground, all motive
power coming from the tail and rear legs. What struck
me at the time was that it's front legs were held
straight out and moving very rapidly; had they been
longer, and the vegetation/water slightly deeper,
there would have been a definite locomotive assist.
Presumably the front legs were not synchronized in a
true flapping motion, but I believe that is a small
step. If you observe people trying to run in waist
deep water, I think you will observe that the hands
are instinctively used in a synchronized flapping
motion on the water surface as a locomotive assist. So
I feel that basic flapping mechanisms may even predate
bipedality and agree w/ GSP in this respect.

2. Immature bobwhite quail pass through a (very!)
short stage where they have wings but cannot generate
enough lift to fly. When pressed, they will run while
flapping their wings to gain an assist; note that this
is not WAIR, but rather WAR, as there is no incline
required. As they become capable of generating enough
lift to become airborne momentarily (altitude <1m),
they maintain the classic extremely-high-wingload
posture; body at approximately a 45 degree incline,
head up and feet outstretched. Then of course they
stall, and flutter down. They seem to have trouble
putting their heads down...

However, if they happen to land in a bush or sapling,
and are then flushed, they naturally put their heads
down as they leave their perch, and are _instantly_
flying in proper adult bobwhite manner. I call this
the groundup-treesdown model, or GUTD, and feel that
it is the most plausible sequence for the evolution of
flight in birds. The strength of this model, as I see
it, is that selection for full-fledged (pun intended)
flapping flight began the instant any one of
potentially many WAR pre-bird species peeled out of a
high place, with no particular environmental or
behavioral prerequisites, thereby maximizing radiative
potential.

In closing I would like to stress what I feel is the
importance of the predatory life-style in the
development of pre-flight and flight
adapt/exaptations. Predators tend to be small, and get
double advantages in the probability sense (predation
avoidance and enhancement) from single
characteristics.

FTW--

Don

--- John Scanlon <riversleigh@outbackatisa.com.au>
wrote:

> 
> My two cents worth on preadaptation to flight:
> 
> Don Ohmes wrote:
> 
> > Actually, if feathers served as camoflage, then
> they
> > would enhance hunting, particularly ambush
> predation.
> 
> And this reminds me of a piece of fiction I was
> working on in the early
> 90's (as a diversion from my thesis) and which has
> languished on a cold
> back burner since then.  I did persuade Ralph
> Molnar, then at the
> Queensland Museum, to read a draft in '95, so I'm
> not just making this
> up now. (Hi Ralph! Enjoying retirement?)
> 
> Anyway, I postulated a small, slender, green
> theropod specialised as an
> ambush predator; its habit is to perch in foliage
> (especially of cycads)
> and grab passing prey with a sudden two-armed lunge.
>  It gets called the
> 'mantis lizard' for obvious reasons; one of the
> other animals I had in
> mind was a very slender green extant agamid lizard,
> Diporiphora superba.
> There must already have been some pretty intense
> selection for
> camouflage, because at the stage of the early to
> mid-Jurassic when I
> 'saw' this little beast it had a fringe of very long
> scales (OK, lets
> call them protofeathers) along the sides of the
> body, tail and limbs
> that are a close match to cycad fronds, i.e.
> shallow-V-shaped in
> cross-section, with a rachis but (as yet) no
> separate barbs, or overlap
> between adjacent vanes.
> 
> Is this the same guy you saw, Don?  I think it
> demonstrates some of the
> ideas you've mentioned, providing a context where
> selection would act
> for long and powerful arms with a swift symmetrical
> power-stroke,
> perching ability, and elaboration and lightening of
> protofeathers before
> any kind of flight became significant (but of course
> when camouflage
> fails against a bigger predator, the critter just
> has to jump off its
> perch - however high that is - and run away). 
> 
> John
> 
>