Re: Pterosaur size

[don ohmes <d_ohmes@yahoo.com>]

"Why is wingstroke amplitude a problem?  The quetz shoulder that I have lying 
here on my desk doesn't have a wingstroke amplitude problem.  Available 
amplitude is far greater than articulated stripwise flapping calculations 
indicate would be needed to maintain level flight in no-lift conditions."

On take-off or other flight close to the ground. As in the wingtip running into 
the ground. Even blue herons have to take a pretty good jump when taking off to 
get ground clearance. A 11m wingspan implies a wing of 5m, right? Even a few 
degrees down from horizontal and the wing is on the ground. I'm sure you've got 
that all worked out in theory, but from the ecological perspective I continue 
to be skeptical.

 "If you're referring to potential launch and 
landing techniques, they meet the requirements for a hypothesis and can be 
either proven as possible or disproven as possible."

Empirically?

"Re flight, I had sort of come to that conclusion myself over the years. 
What I find enthralling are the many ways in which animals address that 
issue and use it to their benefit.  None of the animals we've been 
discussing are particularly close to atmospherically constrained flight 
issues.  Several of them are close to launch constraints due to avenues 
taken by their predecesors -- others aren't.  I note in passing, that geese 
and swans have been reported by pilots at altitudes of 17000 feet, where the 
density ratio is 0.59 (a 41% reduction from sea level). "

You are changing the subject. What does a 15lb goose flying in 50 mph winds at 
59% have to do with a 110lb bird with a full crop trying to make a getaway from 
a carcass on flat ground on a damp, still day? Or a Rueppels vulture at 35000 
ft, for that matter? Koford (1966) says modern condors have limited success 
without a downhill slope and headwind. By the way, the condors released in AZ 
are 10-15% smaller (weight) than the largest San Jose birds of the 19th 
century, if my data is correct. 

"You are proposing that density variations of 15% are critical."

No, I'm not. Never did. I said that 15% might convey more benefit than would be 
thought, cited a personal observation to support that, and expressed the belief 
that the maximals needed all the help they could get. The 15% figure was chosen 
because it is about the most you can obtain w/out hypothesizing variations in 
N2 mass, and I seemed to get significant effect at that pressure. When you talk 
about N2 variations, geochemists start acting like you are trying to steal 
their kids, and I wanted to avoid trouble, like being misquoted, and having to 
repeat myself. Not that there is any chance of that. Why are people so wedded 
to steady-state N2? The emotional reaction when you question that 
anti-uniformintarian assumption reminds me of when you tell certain people 
their ancestors were monkeys. It is weird. Although I did read a paper by Marc 
Javoy that mentioned a post-Archean N2 mass of 3x present day. If memory 
serves, he mentioned subducted nitrogen being locked up in "osbornite".
 That's it, though

Heh. I even had a burned-out acidhead panhandler in California tell me that 
"the Illuminati" would kill or otherwise destroy anyone who tried to prove that 
we were "losing air". Why this was supposed to be, I don't remember. This was 
about 35 years before I ever even thought about steady-state N2, and I thought 
it was pretty humorous. So there is a certain folk history, I guess, like w/ 
cars and oxygen in the '20's. But I digress.

"That occurs at an elevation of about 5500 feet, where the density ratio is 
0.85 (a 15% reduction from sea 
level).  Does that mean that a modern bird suited for flight near sea level 
would be ground bound at 5500' MSL ?  Does that hold in practice?  Swans (a 
group that includes the heaviest individual bird known to flap by means of 
continuous flapping) spend a lot of time near sea level, but certainly 
aren't limited to elevations less than 5500 MSL."

Sorry. I don't see the relevance to Quetz, Argent, et al. Or any argument I 
have ever put forward.

"If so, then it would be even less friend
both of whom 
face more flight strictures than pterosaurs."

Don't doubt it.

"You yourself restricted the statement to birds.  Re-read it     :-)"

C'mon. Did not. I wrote:"I think the current size limit for flapping flight is 
below Argentavis..."
Flapping flight. Not bird flapping flight. 

And also I wrote: "...even considering that some systems are superior to 
others..."
As in system 1 is pteros, system 2 is bats... you say the pteros are the best. 
I don't argue that point.

"Is that speculation, or a demonstrated fact?"

Fact. Plot maximal volants in timeslice fashion. Stick to birds if you want. 
The trend is there, relevance is debatable. Although the correlation on the 
chart I did 15 years ago is -.75 (past to present), not -.95. Sorry about that. 
If it were only birds, or only volants I would say " random chance"....


"True.  I didn't imply that it was. "

Kind of out of context, then, for guy selling horsewhips. }: D

Don

----- Original Message ----
From: jrc <jrccea@bellsouth.net>
To: d_ohmes@yahoo.com
Cc: dinosaur@usc.edu
Sent: Wednesday, December 13, 2006 4:37:03 PM
Subject: Re: Pterosaur size


> ------- Why not?  Current atmoshperic conditions wouldn't stress either 
> them
> or any of their ancestral line.......
>
> You keep telling me that, but I'm skeptical. Wingstroke amplitude and 
> landing speeds are 2 reasons why.

Why is wingstroke amplitude a problem?  The quetz shoulder that I have lying 
here on my desk doesn't have a wingstroke amplitude problem.  Available 
amplitude is far greater than articulated stripwise flapping calculations 
indicate would be needed to maintain level flight in no-lift conditions.

And why is landing speed a problem?  It sounds like you may be expecting the 
animal to have to land as speeds approaching the steady-state stall speed. 
Needless to say, they don't have to do that.  Again, its a matter of 
technique.

>The trend I see in the fossil record is another. Your statements about 
>launch modes are interesting, your knowledge base is evidently 
>comprehensive, and for all I know you are right. But I am still skeptical.

Which is certainly your prerogrative, and a conservative stance.  I applaud 
that.

> Like I said, it is an opinion.

I got lost.  What's an opinion?  If you're referring to potential launch and 
landing techniques, they meet the requirements for a hypothesis and can be 
either proven as possible or disproven as possible.

> Too bad we aint got a few million years, because I have been known to 
> place a bet.

If making a bet would give me a few million extra personal years, you'd be 
on (and I wouldn't care who won   :-)

> The physical properties of the atmosphere constrain many processes, 
> including flight.

Re flight, I had sort of come to that conclusion myself over the years. 
What I find enthralling are the many ways in which animals address that 
issue and use it to their benefit.  None of the animals we've been 
discussing are particularly close to atmospherically constrained flight 
issues.  Several of them are close to launch constraints due to avenues 
taken by their predecesors -- others aren't.  I note in passing, that geese 
and swans have been reported by pilots at altitudes of 17000 feet, where the 
density ratio is 0.59 (a 41% reduction from sea level).  You are proposing 
that density variations of 15% are critical.  That occurs at an elevation of 
about 5500 feet, where the density ratio is 0.85 (a 15% reduction from sea 
level).  Does that mean that a modern bird suited for flight near sea level 
would be ground bound at 5500' MSL ?  Does that hold in practice?  Swans (a 
group that includes the heaviest individual bird known to flap by means of 
continuous flapping) spend a lot of time near sea level, but certainly 
aren't limited to elevations less than 5500 MSL.

> It is my opinion that a slow directional change in the physical properties 
> of the atmosphere provides the best fit for the fossil record as a whole. 
> In my opinion, the direction is such that "tomorrow" (say, 10 mys) will be 
> even less pterosaur-friendly th
 bats, both of whom 
face more flight strictures than pterosaurs.
>
>> In fact, I think the current size limit for flapping flight is below
>> Argentavis, and somewhat above the largest birds living...
>
> ---------I tend to agree with this particular statement, but what do avian 
> limits
> have to do with pterosaurian (or bat) limits?
>
> Actually, you don't agree, except as it applies strictly to birds.

You yourself restricted the statement to birds.  Re-read it     :-)

> I meant to include bats and pteros. See below.
>
>> even considering that some systems are superior to others, which to my
>> mind just increases the variance, but doesn't affect the slope of the
>> moving average. Just an opinion.

 
> But it is there. (insert - moving average)

Is that speculation, or a demonstrated fact?


> You may feel that it is irrelevant, and you may be right to dismiss. But 
> it is there.
> Largest volants in time sequence: Q. n, various pseudodontorns, A. mag, 
> Pseudodontornis, T. incredibilis, T. merriami, California Condor.

You are mixing and matching two different structural systems, and three 
types of flight mechanics.  Apples and oranges, perhaps ?

> In wing span sequence: Q. n, A. mag, various pseudodontorns, 
> Pseudodontornis, T. incredibilis, T. merriami, California Condor.

Same statement applies.  Or, oranges and pears if you prefer   :-)
As an aside, when did A mag get to be older than the psuedodontorns?

> If you accept that the trough after K/Pg is caused by a catastrophic 
> event, and smooth accordingly, you get a distinctly non-fluky looking 
> curve that is ~100 mys long, without need for any statistical manipulation 
> whatsoever. The negative correlation of wingspan to time (past to present) 
> is better than -.95.

Women's skirt lengths in the 20th century show a strong correlation to the 
manufacture of horse whips.  Does that mean that changes in one caused the 
other?

>Corrections appreciated. I find it compelling.

I'm sorry, I don't.  I do find variations in launch technique interesting 
though.

> But that is just my opinion. Correlation is strong even if you punch in 
> some of the comeback kids post-K/Pg...

Wanna buy a horsewhip?

> -----------------Individual birds do it in a few days, in response to 
> changes in wing area
> because of the moult.  Birds that lose, say 30% of their wing area during
> the moult also tend to lose about 30% of their body mass (which does 
> reduce
> their efficiency, but also allows them to continue to fly without much
> alteration of performance).
>
> Yes. Although that is not morphic optimization in the evolutionary sense.

True.  I didn't imply that it was.