Re: Pterosaur size

[don ohmes <d_ohmes@yahoo.com>]

From: jrc <jrccea@bellsouth.net>
To: d_ohmes@yahoo.com
Cc: dinosaur@usc.edu
Sent: Saturday, December 16, 2006 8:23:04 PM
Subject: Re: Pterosaur size


----- Original Message ----- 
From: "don ohmes" <d_ohmes@yahoo.com>
To: <dinosaur@usc.edu>
Sent: Saturday, December 16, 2006 6:06 PM
Subject: Pterosaur size


>
>
>To verify our points of agreement; the big girls existed (11m or bigger
> wingspan),

Yes, though the max estimated span for birds is on the loose order of 6.5-7 
meters.

> they could fly,

Mostly.

> and the upper size limits of volancy generally are
> constrained by launch and  landing capability?

Yes.  launch more than landing.

> So, anyhow, what are you using for wingload?

Depends upon the animal.  Since pterosaurs tend to have similar aspect 
ratios, and somewhat differently from birds (which show more variation in 
planform), their wingloading tends to increase with wingspan.  For Qn, it's 
roughly 4.3 pounds per square foot, or about 21 Kg/S.M. -- about the same as 
the most heavily loaded birds, but greater than the largest volant birds. 
However, for both birds and pterosaurs weight can vary substantially during 
the course of a single flight (as much as 50% for some birds).
>
>Relative to a given process, selection occurs at the point of maximum 
>stress,

And at points of average stress, and minimum stress, and so on, ad 
infinitum.

---------There is a functional bottleneck at the point of maximum
stress. All life events are not created equal as determinants of
genotype. 



> and it isn’t surprising that you don’t observe a large change in behavior 
> or
> morphology from the point of maximum stress to the point of least stress. 
> The appropriate question is; how will they
> perform in a habitat range of .5atm-.85atm, or .68-1.15atms?

It depends mostly on their launch technique.  For example, I once calculated 
whether pterosaurs could fly on Mars (where surface pressure is about the 
same as at 110,000 feet here.  It turns out that if you could supply them 
with oxygen, keep their blood from boiling due to the low pressure, and keep 
them from freezing -- some of them could.  But they couldn't launch or land. 
Well, actually -- they could land, but not in one piece.


>
> To use an analogy-- I weigh 100kg,
> and like to jog on the beach (boy, I wish, but that’s why I like thought
> experiments).

I can identify.  I weigh about 97 Kg.

>Once a week, I run a marathon with 15kg strapped on my back. I am
> optimized to running weekly carrying 15 kg, and therefore finish my 
> marathon,
> which is good for me ‘cause I’ll die if I don’t. The beach of course, is 
> just
> the beach. You observe my performance and notice that I seem to be using 
> approximately
> the same running style 7 days a week. You reason that I can easily cope 
> with a
> 15% change in my weight.

Well, no -- that's not an apt analogy for what we've been talking about.

> Wrong. This observation tells you nothing about my
> ability to cope with a lifestyle wherein I weigh 115kg on the beach, and 
> 132kg
> while running my mandatory Saturday marathon.  Granted, a day at the beach 
> is just a day at
> the beach, but Saturdays are a bitch. Or more to the point, how much are 
> my
> chances of a long life improved if I weigh 85kg and marathon at 98… 
>  “small”
> improvements in ambient conditions lead to small improvements in athletic 
> performance
> lead to very large improvement in the probability of success, and by the 
> math,
> a bird flying in +15% has lost 15% of its weight.

Ur, uhh,  No.  It doesn't work quite that way.

> That is the equivalent of the
> real me losing 36 lbs. Makes a HUGE difference.

Let me ask a flight question.  Let us arbitrarily assume that you are a 
bird, or a winged whatever, and that from a height of 1000 feet in no-lift 
conditions, you can glide a distance of 20,000 feet.  Now, let's add 15% to 
your weight.  Without flapping, how far can you glide in the same 
conditions?  Now, let's reduce your weight by 15%.  How far?

--------- Ain't 20:1 high for a whatever? Just asking. Going from 
thin limits.
However, remember we agreed about that launch/flight/landing thing
being what counts? How the hell you get way up there at a 1000'? How do your 
power requirements vary? I
don't start my marathon from the halfway point, although I have been called a 
winged whatever. When I talk about
flight or volancy in the context of biosystems, I mean the whole cycle. So I 
need a more precise term
that isn't as hard to type as 'ecologically viable volancy' or
whatever. Flight cycle, maybe?


> and the Andes. Blackbirds that nest at 2500’ have lower
> wingloads than sealevel nesters.

Not for any reason to do with flight -- it's actually to do with launch, and 
the variation between individuals or for one individual over time -- varies 
by more than the difference in density due to the 2500' change in altitude.

----------I don't understand what you mean, but I think I probably disagree.

> Seems like if you could determine minimum launch density, you could adjust 
> to sealevel, and get a eco-perspective on max viable swan size.

That's true, for their present bauplan.

-------------------- Damn. I was really hoping there was an answer to the max 
observed launch altitude re cygnus. Think there is one, or do they launch right 
on up to .59 atm?

> Checking is good, right?

Yup. 

--------- What this country needs is a really effective placebo. But beer 
works, usually.

Don