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Re: A whole lot of trouble....



Stephen Throop wrote:

>He suggested that dinosaurs first had feathers.  They would flail their
>limbs for balance when they jumped from limb to limb.  That's how they
>learned by accident to glide.  Then the gliders evolved the structures
>necessary for powered flight.
>
>That explanation seems way out on a limb.  It's like expecting flying
>squirrels to evolve into bats.  As the farmer replied when asked
>directions, "You can't get there from here."  

Flying squirrels, no.  Dermopterans (or in any case, something close to
them), a whole different kettle of archontan.

>The requirements for flight are so different from those for gliding that
>before gliders ever learned to fly, countless of generations would have
>had to evolve senseless changes.

Although I am puzzled by the term "senseless changes" (since when do new
character states have awareness?), Ostrom and others (myself included) DO
find problems with standard models of vertebrate gliding in the origin of
bird flight, for just this reason: there is no evidence for the typical
features of gliding in modern or fossil birds.

>The same consideration argues against the theory that flight evolved
>from fleeing (i.e. flight).  Until a species could fly, the evolving
>changes would have made it a slower runner.  Flying dinosaurs would have
>lost their ancestors before the ancestors had any offspring.

Or they could have scampered up a tree...  Or had lots of babies.
Hypsilophodontians (not fliers!) survived very well from the Middle Jurassic
to the end of the Cretaceous without any spectacular changes in their
anatomy, and may have simply taken advantage of the buddy system.

>The big picture is a bigger puzzle.  Look at scale.  For animals of the
>same proportions, mass varies as the cube of linear size.  Surface area
>varies as the square of size.  That means wing loading varies in
>proportion to size.  Meanwhile, the force to vibrate a wing at a certain
>frequency varies as the fourth power of size.  
>
>This means a wing on a larger animal must maintain more pressure but
>can't be flapped as fast.  That's why it would take a miracle for a big
>bug to fly in the manner of a housefly.  It's also why the bumblebee is
>thought to be as large as possible for a flying animal of that design.  
>
>Still, in the dinosaur days, there were flying bugs that were built like
>modern species except that they were much bigger, perhaps ten times. 

Ummm, no there aren't.  There were BigAss (tm of WorldWide Pants) dragonfly
relatives in the Carboniferous, long LONG before the rise of dinosaurs, but
these do not fly in the same mode as a bumblbee.  They probably flew in the
same mode as dragonflies (big surprise...), and there is no strong evidence
to support the idea that extant dragonflies are the maximum possible
operational size for their design.

[Indeed, I recently looked back at an article on them in "Air and
 Space" (a magazine put out by the Smithsonian Institution).
 Dragonfly wings can produce hellatious amounts of lift.  -- MR ]

>How could they possibly have flown?

See above.

>In scale, flying dinosaurs present bigger problems.  One had a wingspan
>of 51 feet!

The largest flying dinosaurs were teratorn birds and others of the Tertiary.
Pterosaurs, on the other hand, did get up to c. 10-12+ m wingspan, but were
NOT dinosaurs.

>In World War Two, an airplane that big would have needed two engines, 3,000
>horsepower, and thousands of feet of runway.  How could an animal that big
>have produced enough power to fly?  Where could it have attained the necessary
>speed?  How could its wings have been strong enough even to glide?

WWII POWERED airplanes were a) made of metal, wood, and other materials,
often denser than bone and flesh; b) expected to fly reasonably faster than
winged vertebrates; c) built to carry people, instrumentation, bombs, ammo,
new copies of Stars & Stripes, etc.

There were gliders then, and are today, which exceed the wingspans of
pterosaurs, are built of very lightweight materials, and yet are still
structurally strong enough to support their own weight and that of a pilot.

Pterosaurs were a) made of flesh and bone; b) probably did not fly
considerably faster than similar sized birds and bats today, possibly even
slower; c) evolved to carry themselves and their gut contents.

>By contrast, a model airplane the size of  a typical hawk can take off
>in two feet with only the power of a twisted rubber-band.  That's the
>effect of scale.  
>
>A bird with a five-foot span has a hard time taking off because its mass
>is so great and its wings are so slow.

Swans, big hawks, eagles, condors, storks, albatrosses, etc. do not have a
hard time taking off, any more than human-sized or larger animals have a
hard time standing up.  Sure, once in awhile they don't make it on the first
try, but the same goes for couch potatoes when they hear the phone
ringing... :-)

>How could a dinosaur with 1,000 times as much mass and much slower wings ever
>have flown?

A hawk with a five foot wingspan has a mass of, what?  1 kg?  2 kg?  3?
(Birders could help on this point).  You are claiming that the big
pterosaurs massed 1000, 2000, or 3000 kg?  This is grossly overexaggerated.
Greg Paul's estimates, the maximum out there, have something like 250 kg for
the biggest pterosaurs.  Do the math...

>Here's another puzzle.  It seems that all flying dinosaurs had long, heavy
>tails.

Ummm, no.  A) The largest flying dinosaurs are birds, and most of their tail
is feathers.  B) The largest pterosaurs are all pterodactyloids, and this
clade is characterized by very SHORT tails.  Look it up.  Forget the
drawings you may have seen in the Far Side or on a Flintstone's Lunchbox:
the big pterosaurs did not have Rhamphorhynchus-like tails.

>Modern land animals carry only little tails,

Modern land *mammals* have only little tails, but mammals are synapsids, and
their major thrust muscles in the hindlimb attach to the hip, not to the
tail.  Modern and fossil diapsids (lizards, crocs, dinosaurs, etc.) have
their major thrust muscles in their tails, and this is the reason diapsids
did (and still do) have such long tails.

>and birds use feathers for tails.  How could a dinosaur have flown with all
>that weight?

See above: a non-argument.

>It's even harder to understand why something as unsuited to flight as a big
>tail didn't soon evolve to a little tail.

That would be very funny.  However, in the evolution of pterosaurs, there is
a shift from long tails in the primitive small forms to short tails, and
then an increase in size.  Similarily, there is a shift from a longish-tail
in the earliest birds, then a shrinking of the tail to a pygostyle and
feathers, and eventually the appearence of eagle-sized or larger birds.
This is just what you might expect.

>Instead, it seems that flying dinosaurs kept their big tails for millions of
>years, until they became extinct.

Nope.

>The origins of flight

[as presented by you]

>present us with several impossibilities.  Flight is only one area where the
>evidence of dinosaurs is impossible.

What exactly do you mean by this?  Trust me on this point (or go check
yourself):  the bones are there.  Dinosaurs were real.

>If the evidence is correct, then it seems that there must be a big mistake in
>our fundamental assumptions about the environment of the dinosaurs.

Let me guess what that assumption might be...  That the Earth was always the
size it is today?  That the atmosphere was always approximately the density
it is today?  That the Earth always orbited the sun in the third orbit in
the system, rather than a physcially impossible orbit around, oh, let me
guess... Saturn?  (The latter brought to you by Ted Holden: the man for whom
Roche's Limit has no meaning... :-)

> Here's how Rob Meyerson, the distinguished orphan vertebrate, quoted Sherlock
> Holmes the other day: "It is fatal for a researcher to develop a theory before
> all the facts are in, because one ultimately tries to twist facts to fit
> theories, rather than develop theories to fit the facts."
>
> Don't worry.  I won't propose a theory.  As you no doubt see, I'm a timid
> fellow who would *hate* to annoy anyone.

No, of course not.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661

"There are some who call me...  Tim."
-- Tim the Enchanter, "Monty Python and the Holy Grail"
---------- subtitle --[Monty Python ik den Holy Grailen]

"Tim?!?  They called me TIM?!?!"
-- Tom the Paleontologist, on seeing "The Ultimate Guide to T. rex" :-)