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Re: Phylogeny of Maniraptora
On Fri, Jun 06, 2003 at 02:49:42AM -0700, James R. Cunningham scripsit:
> Graydon wrote:
> > Are there any non-volant organisms that really glide, rather than
> > parachuting? Anything among the flying snakes, flying squirrels,
> > draco lizards, etc. that can, frex, get energy out of a headwind to
> > land higher than they started?
> You realize of course, that there is no way to extract energy from a
> headwind once you have reached steady state velocity after initial
> launch. On the other hand, it is possible to extract energy from wind
> shears at any time.
I was thinking of watching seagulls hang in a strong breeze when I wrote
that, which is probably not a good example of gliding, and, as you note,
not a good example of getting energy from a headwind as such.
> > I'm trying to get at a distinction between using aerodynamic forces to
> > reduce sink rate (parachuting) and turning velocity into actual lift
> > (gliding).
> In oversimplification, the distinction is that in parachuting, the drag
> vector is greater than the lift vector and the drag vector is oriented
> mostly upward (in what is usually taken as the lift direction). And in
> gliding, vice versa and with the drag vector being oriented mostly
> horizontally. The distintion is really more whether the drag vector is
> primarily parallel to or perpendicular to the chordline.
What I was really after was a distinction between lift by applying
energy stored internally (flying), by using energy available in the air
(gliding), and by using energy available from gravitational potential
(parachuting), only that's wrong, as a definition, and it as getting
tangled with a sense that a parachute can't actually go *up*, but a
glider or a flyer can.
> > I think the whole glide/flap for power thing gets tangled in this;
> I don't. I do think that some of the 'explanations' get tangled in it.
> > an organism doing attitude control and fall-retarding things *isn't*
> > gliding, it's parachuting,
> That depends upon whether the drag vector is primarily parallel to or
> perpendicular to the chordline while it is doing these 'things'. Which
> is the case for the organism you describe?
I was thinking of flying squirrels, which are probably gliders by your
definitions given, but which (so far as I know) cannot wind up higher
than they started even with perfect conditions.
> > and it'll do whatever it takes to get its attitude on impact right,
> > because it has to get it right.
> I'll drink to that. Though I've noticed that albatrosses don't always
> get it right upon landing and sometimes go fanny over teakettle.
I've seen a few gulls doing non-flapping water landings do that, too.
What I was mostly thinking of, though, was domestic chickens, which
can't really fly, but which expend immense amounts of energy on attitude
control if you push them off the ridge line of the building they're
sitting on instead of nabbing them and stuffing them in a sack.
(Good flyers, no; good escape artists, yes.)
> > You get something like flapping from the predatory stroke if you
> > push a basal maniraptoran out of a tree; it may not do any good, but
> > that's what its arms _do_ when trying to move rapidly, they're not
> > the peculiar wide-range-of-motion things people have got. If it's a
> > maniraptoran, it can flap. (maybe not *well*, but it can flap.)
> That's true. Just as it can flap while running. Or while standing
> about or jumping up and down.
Sure; I don't mean to attach any important to the tree, I was trying to
conjure up a mental image similar to 'find Dromeosaurus' great great
grandpappy; drop him from a height. Look, flapping!'
The Metro Toronto Zoo has a pair of ostriches off in a *big* pen by
themselves; when I was there last summer, the male ostrich went into a
full territorial display (I don't think he approved of my hat) and, a
little later, started making some indications of interest in the hen.
She ran off; not flat out, but running, which is the only time I've ever
seen an ostrich really run. Her wings were moving in small flapping
motions; I don't think the two sets of limbs are completely decoupled
unless something comes along to provide pressure *to* decouple them.
> > The trick is not identifying when lift comes in; 'assisted vertical
> > running' makes it clear that there *is* a nice shallow ramp for the
> > utility of lift for small maniraptors, one that can't be discounted
> > from fossil evidence even if it never took place in pre-volant
> > species.
> Sorry, I miss your point (wee hours on my part, perhaps). Would you
> elaborate please? What is the trick involved?
Dr. Kenneth P. Dial; he calls is WAIR, wing assisted incline running.
That's running up the slope/tree trunk using wing assist to maintain
traction and climb steeper slopes; we can't tell if the early
maniraptorans that were starting to develop the ability to apply useful
amounts of force to the air did this on the way to flight feathers,
wings and flying, but we can't discount it, and it provides a way for
small variations in slope climbing ability to be subject to strong
selection pressure -- use a predator escape -- so there's a ramp for
going from predatory-stroke-plus-feathers to
> > Somewhere, though, there's a biomechanical analysis that indicates
> > the sustained load bearing capacity of the arms; it's when that
> > passes some multiple of body weight that you've got a real flyer.
> > I'd *expect* that number to be a bit over two, but that particular
> > wild ass guess isn't even sophisticated.
> Doesn't that sort of depend upon the duration of the anticipated
I was thinking that it would depend on the peak stress as you launched
yourself up, into the air.
> How long do you need to be able to maintain the multiple of
> two before you are a flyer?
I'd say that if you can go from point A to point B, where point B is ten
or more times your head-to-foot height above point A, under your own
power and in the air, you're a flyer.
I can't think of any way to test that in the fossil record, though. On
the other hand, if you are a maniraptor and your arms have got strong
enough to hold up n times your body weight, that *might* be detectable
in the fossil record.
I think with what we know now, feathers and flapping are a given; it's
ability to grab onto the air and climb that provides evidence of powered
> Twenty seconds? Twenty days? If it weren't for gusts, turbulence,
> turning forces, and safety factors, I'd expect the number to be about
> 1.2 to 1.4 (optimum flapping occurs when the CL ranges by a factor of
> about plus 0.2 to minus 0.2 (range 0.4) around the optimum CL. For an
> animal with an appreciable aspect ratio, optimum CL is often about 0.8
> to 1.0. Be aware that this is an extreme oversimplification on my
> part and don't hold me to these exact numbers.
Wouldn't dream of it.
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