Next article. Why really big dinosaurs couldn't walk.

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Just what the world needs, 250 kilo, quadupedal "marabou storks" that were efficient ground runners. Another creature like the T-rex, that if it wasn't already extinct, it would be.

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In your rush to call everyone "entrenched" or closed-minded or "limited" you fail to note that the "limit" here has a very natural boundary: that point at which the evidence stops. - JayUtah

Science fiction was never meant to be an educational tool. - Editor Amazing Tales

Although, as the PLoS review I linked to shows, there's a lot of inland material, too:Grant Hutchison

Thanks Grant.

It seems that pterosaurs lived in a variety of habitats.

I was always under the impression that pterosaurs had a wide wingspan relative to their bodies, but it seems the opposite is true. (I love learning something new!)

As some appeared to be good walkers, perhaps some types walked up to high ground and then glided down onto their prey, using their bulk to stun their prey?

The review is specific to the azhdarchids, which (the authors report) have unusually short, deep wings for pterosaurs. I think some of the other pterosaurs would fit better with your original impression.
In birds, wing shape correlates strongly with lifestyle: if the azhdarchids were birds, we'd expect them to be static soarers with a tight turning circle, rather than dynamic soarers with a shallow glide angle; more condor than albatross.

Grant Hutchison

Thanks for the good link Grant. Although you're going to have to help me out here:
Was Dr Sato right? (OP)
Or was it the case that, as you imply in your last post, pterosaurs were as varied as modern-day birds?
Thanks

Well, well, well. Someone's not discouraged I see.

'Pterodactyl-Inspired Robot to Master Air, Ground, and Sea'
Press release: http://www.geosociety.org/news/pr/08-58.htm

The abstract: http://a-c-s.confex.com/crops/2008am...aper47647.html

From what I've gleaned, I don't think Sato every claimed that pterosaurs weren't a very varied bunch; his remarks are clearly aimed only at the big fellas, like the large azhdarchids described in the PLoS review.
The review suggests that these big fellas occupied a niche we don't have in modern birds: large ground-based hunters that could also, once into the air, do well with thermal soaring. Sato's comments provide a bit of a caveat to that scenario, since he's saying these beasts would have trouble getting into the air: they'd need a head-wind and a bit of a take-off run. They'd also (if Sato is correct) need to land when thermals failed. But to some extent the PLoS review complements what Sato was saying: if these things were efficient ground hunters, then a few calm days weren't a disaster for them. They were using occasional soaring as a way of shifting their hunting grounds, rather than relying on flying every day to get food.

Grant Hutchison

Thanks Grant. An excellent point I think:

Didn't you see the pictures in the link? They are good ones. Too big to up load here but here's two good direct links:

http://www.plosone.org/article/slide...e.0002271.g008

and:

http://www.plosone.org/article/slide...e.0002271.g009

Remember these things weigh about five hundred pounds. That's heavier than most lions.

__________________
In your rush to call everyone "entrenched" or closed-minded or "limited" you fail to note that the "limit" here has a very natural boundary: that point at which the evidence stops. - JayUtah

Science fiction was never meant to be an educational tool. - Editor Amazing Tales

Here ya go BigDon. A bit of size comparison.

Okay, I'm officially glad we don't have that niche Mr. Hutchisen mentioned anymore.

Keeping poodles and weiner dogs is hard enough with just the red tails (hawk) to deal with. Definately have to keep an eye on the children too

__________________
In your rush to call everyone "entrenched" or closed-minded or "limited" you fail to note that the "limit" here has a very natural boundary: that point at which the evidence stops. - JayUtah

Science fiction was never meant to be an educational tool. - Editor Amazing Tales

Though remember when you look at that picture that mammals are several times denser per volumne than even dinosaurs, much less these flight adapted giants.

That giraffe weighs eight times as much as that azhdarchid. Roughly two tons for a stoutly built giraffe. Giraffe could probably beat the crap out of it. Giraffe's neck alone weighs 400 pounds.

__________________
In your rush to call everyone "entrenched" or closed-minded or "limited" you fail to note that the "limit" here has a very natural boundary: that point at which the evidence stops. - JayUtah

Science fiction was never meant to be an educational tool. - Editor Amazing Tales

I’ve been looking at the planform diagram from the article, and wondering how Q. Rhamphorhynchus achieved stable, level flight:

http://www.plosone.org/article/slide...e.0002271.g005

From the diagram:

1. The wings are at the back of the body in flight posture.
2. Relatively large mass of head and neck.
3. Unlike birds, no horizontal stabilizer.

According to my amateur analysis:

4. (1), (2) and (3) mean that the centre of gravity is far in front the centre of pressure.
5. (4) means a severe nose-down tendency in flight, i.e. a tendency to enter an uncontrolled dive. Q. Rhamphorhynchus would be unstable in flight.

Solutions?

1. Carrying head and neck above the centre of gravity during level flight, to introduce a counter-balancing nose-up tendency?
I have an odd feeling that I've seen or read about this posture somewhere, but I can't remember where or when

2. Canard wings? Horizontal stabilisers (tail)? (aircraft solutions)

Help!

You might wonder the same thing about a swan. Flight muscles are big and dense, and the centre of gravity is always farther back than you think.
Herons fly with their necks recurved, but many long-necked birds keep their heads forward.

Grant Hutchison

Swans have tails!

recurved is the word. Thanks

In the diagram, I noticed that Q. Rhamphorhynchus could be said to have a double-tail, almost like an F18.
But I'm not sure if this use would be practical. The legs would have to be hyper-extended and the lifting surface would be distorted.

So? Their tails are made of feathers, which aren't famed for their density. The tail is a light, stiff control surface, rather a balance for the extended neck.
Pterosaurs have legs that extend behind them, which they can use for both balance and to support a winglike control surface, the cruropatagium.

Grant Hutchison

I agree Grant! But that's exactly what horizontal stabilizers do. They're an aerodynamic surface; as one of their functions is to generate aerodynamic lift (in the downward direction for swans), that provides a nose-up pitching moment about the swans centre of gravity. This is many times the simple effect of the mass of the tail shifting the CoG backwards, or of 'balancing' the head and neck around the CoG.

Just to make it clear, I'm definitely in the 'large pterosaurs' flew camp. Just trying to understand their aerodynamics. Love the subject and I love aircraft.

That's one I'd not heard before, and I guess my physical intuition is making me a bit dubious. The generalized bird tail generates conventional upward lift, with the lift from the wings placed a little ahead of the C of G in order to compensate. (The tail of course does other smart things like helping with steering, reducing induced drag and airbraking.)
But you're saying that the swan is using that little short tail with some sort of unusual reversed curvature in order to produce significant downward "lift"? I'm not saying you're wrong, but I'm pretty surprised.

Grant Hutchison

I have no idea Grant! I'm just assuming that might be the case, because of the swan's great big long neck, and the position of it's head in flight.

You're right about this:
The planforms of most birds look more like those of the condor and albatross shown in the diagram. Whereas that of the pterosaur looks more like a swan's on steroids.

And I like what you pointed out earlier:
But, I keep coming back to that planform and no tail. You're the expert Grant, any research you can dig up? It's bugging me!

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"a huge wingspan (some 20-25 feet ..."

"The whole animal probably weighed about 25 pounds, only slightly heavier than the largest flying birds."

That's crazy talk!

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Aw. I thought you were going to treat us to some nice biophysics ...

The pterosaurs still have more of a rear aerofoil than many flying creatures: some bats, for instance. So if the C of G is reasonably placed, I'm thinking an absent tail isn't a showstopper.
I've a couple of textbooks dealing with the physics of animal flight at home. If I reach home at a reasonable hour, I'll see what I can find.

Grant Hutchison

Oh sure. Ignore my excellent link.

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I haven't Robinson! A most excellent link.
In fact, I carried on to here:http://www.ucmp.berkeley.edu/vertebr...ight/pter.html

From which:
So I was trying to find out how the balance problem was solved for the larger, later sub-group.

Sorry! And thanks

By the way, did you know that Paul MacCready (he who built Gossamer Condor and Gossamer Albatross), built and flew a robotic half-scale Quetzalcoatlus in the 1980s? The pictures I've seen of it show a very similar planform to the one in my linked article. And it flew.

Grant Hutchison

[QUOTE]
"... about 25 pounds, only slightly heavier than the largest flying birds."

[QUOTE]

Wrong. WRONG WRONG WRONG.

Heaviest flying birds - kori bustard and great bustard, at over 40 pounds. What is with these people? You can find that information by Googling "heaviest flying bird"!

And someone should calculate the wing loading of azhdarchids. It's probably pretty good, actually - 20-pound Harpy Eagles fly with some pretty heavy bodies for their wingspan. (A lot of tropical eagles have weird wings.) And they're a lot better flyers than bustards.

Chatterjee and Templin came up with a figure of 72 N.m^-2 for Quetzalcoatlus, using 70 kg as an estimate of its body weight. That's at the light end of the many and varied weight estimates for the beast, but it's pretty comfortable. If Quetzalcoatlus were twice that weight, it would have the wing loading of a Canada goose; three times the weight, and it would still be under the wing loading of a mute swan.

Grant Hutchison

Good, because 210 kg is a LOT more believable than 70 kg (that's what a lot of that Witton & Naish work is about). I don't even see where that estimate came from -- how can something 4 meters tall with a 2-meter skull and a 12-meter wingspan weigh as much as a small human?

If the wing loading is that low, I'd be prepared to believe an even heavier azhdarchid...

That is good news! Especially as it was a Quetzalcoatlus.
Pterosaurs as a whole seem fine; it's the Azhdarchidae, with their long, stiff necks, that have me stumped. They look like flying guitars...