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Re: Pterosaur size


----- Original Message ----- From: "don ohmes" <d_ohmes@yahoo.com>
To: <dinosaur@usc.edu>
Sent: Wednesday, December 13, 2006 7:32 PM
Subject: Re: Pterosaur size


"Why is wingstroke amplitude a problem?

On take-off or other flight close to the ground. As in the wingtip running into the ground.

It's no more of a problem than for any other animal that flies close to the ground (or water). There is fairly strong evidence that indicates that Quetz may have been a skimmer, and the wingtips appear to be designed to survive waterslaps (or ground slaps as the case may be). There are no severe physical restrictions on the Quetz shoulder plunge articulation.

Even blue herons have to take a pretty good jump when taking off to get ground clearance.

As do most any animals that launch from the ground. It's no more problem for pterosaurs than for other animals (seemingly less).

A 11m wingspan implies a wing of 5m, right? Even a few degrees down from horizontal and the wing is on the ground. 

I think you're kidding, but am not sure.

I'm sure you've got that all worked out in theory, 

Let's just say that the geometry, skeleton, and physics work.

but from the ecological perspective I continue to be skeptical.

I have no problem with that, but I think you've just said that no animal of any type can fly close to the ground. I disagree with that. 

"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?

Quantitatively.

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. 

How so?  Density altitude is density altitude.

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? 

Try a 13 Kg swan vs. a 19 Kg pterosaur.  The difference isn't so extreme.

Or a Rueppels vulture at 35000 ft, for that matter?

Then you agree that changes in atmospheric density aren't important to flight?

"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.

About the equivilent of a 5500 foot change in altitude, so testable in today's atmosphere.


"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.

Mike, do you see its relevance? 
"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.

I quote: "In fact, I think the current size limit for flapping flight is below
Argentavis, and somewhat above the largest birds living".

I interpreted that to be a statement about birds in general and Argentavis in particular.

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.

I didn't say that. They all have their specialties. Pterosaurs are better at a number of things, but can't survive extended durations that aren't suitable for soaring -- and it killed 'em.