Re: Dinogeorge Digest #5

["James R. Cunningham" <jrccea@bellsouth.net>]

Dinogeorge@aol.com wrote:
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> I've noticed a correlation that might be worthwhile investigating further: in
> both pterosaurs and birds, the relative size of the braincase increases at
> about the same time as the tail shortens. I suggest this is part of the
> conversion from stable flying to unstable flying, when the animal begins to
> rely less on the tail and more on its brain power to control its flight.

I would agree with the above.  In fact, I thought it was a given.

> Unstable flight is possible only if the brain is an active part of the flight
> control system (so to speak).

This is only partly true.  it presents a significant problem in late,
long necked pterosaurs.  Of the two normal modes of the longitudinal
equations of motion, the brain could be used to control the phugoid
mode, but I would suspect signal delay (travel time) from the brain to
be a problem in controlling the short-period mode.  Similarly, in Qn the
18-24 foot long path between the brain and the proximal metacarpal joint
and spoon-shaped joints between phalanges 1&2 and 2&3 (the three joints
which affect gust load alleviation) might well delay the signal long
enough to make primary control of these joints from the brain unusable
or even destabilizing.  Also, it seems problematic that the pencil-lead
diameter of the cervical neural passage would allow the signal density
required for control of the short-period mode(which is controlled at
shoulder, wrist, and hips) and gust alleviation plus other bodily
functions.  Perhaps (I throw this out as a conjecture rather than as a
hypothesis) the brain did optical processing required for overall flight
control and terrestrial operations, while local flight response was
provided by a combination of automatic deflections in the outer wing and
reflex signals generated at or outboard of the shoulder and biased by
optical processing from the brain.

Some of you guys out there who are into neural signal velocities, how
long would it take Qn to pass a signal approximately 24 feet from the
brain to the joint between Ph 3&4 ?

> If this is so, one might predict the existence
> of birds and pterosaurs with somewhat enlarged braincases and long tails, but
> never the smaller braincases and short tails.

I agree with this.

> It is mainly the enlargement of
> the braincase that results in the rearrangement of the cranial bones from
> typically reptilian to typically avian in birds, also enlargement of the
> orbits--which could well be part of the same flight-control-improvement
> process.

I fully agree that enlargement of the orbits and of the optical
processing area of the brain is a key part of the
flight-control-improvement process.

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> This is not some kind of untested assumption. I've yet to see a published
> scenario in which avian ornithoptering flight evolves with any facility from
> cursorial flightlessness. The physics is against it, 

I think the physics is for it, but that's why they make Fords and
Chevrolets, so we can all make our own choices.

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> It is not a simple modification of some quirky
> behavioral pattern; if it were, there would be hundreds of different kinds of
> flying vertebrates instead of only three.

How true!!
I gotta stop.  My daughters want the phone.
Good points George - even the ones I don't agree with.
                Best wishes,
                JimC