[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Archaeopteryx running & CNN report on the feathered dino

Williams, Tim wrote:

  >>Of course not.  My thumbs are singularly well adapted for holding
ball-point pens.

 > Ah, that's cheating.  Ball-point pens are *designed* to be held by
the human hand.  :-)

Is it?  Are you sure that ball-point pens are not designed as
simulations of sticks?  Are sticks 'designed' to be held by the
human hand?

  >>Quetzalcoatlus species ........  How does the puny sternum make it
ineffective? (in flight)

  >As a flapper, perhaps.

It was a superb flapper, though it operated as a motor-glider and didn't
flap for very long at a time.  It powers its wings
somewhat differently than birds do and consequently a large sternum and
keel aren't required.  My point is that there is
more than one way to skin a cat.

 >  I admit I'm a dingus when it comes to pterosaurs - but aren't these
enormous pterosaurs thought to spend most of their > time soaring?

Most, but not all of the time.  The big azhdarchids were superb
short-term flappers, tending to move their glenoid
somewhat lower on the scapulo-coracoid to allow for an improved upstroke
and increased mobility in the wing.  Q
species wasn't really an enormous example, spanning about 4.8 meters
with a weight of about 20 Kg (about the same
weight as a 6.8 meter Pteranodon).

  > Aerodynamically, this is extremely challenging (and probably the
most derived of all aerial behaviors); but at the same > time soaring is
less demanding on the muscles and skeleton.  (If I'm totally wrong on
this, don't hold back!)

You're totally wrong.  Climbing out, landing, and remaining clear of the
ground when atmospheric lift wasn't available
within gliding range required active work during calm conditions, and
these animals had substantial wing loadings, so were
earning their keep during these phases of flight.

 > Now we're talking 'cruising'.  For a primitively poor flier that
couldn't flap well, this would just be 'gliding', wouldn't it?

No.  Why would you think archie didn't flap well (by that I mean in a
way consistant with his life style)?  And what would
make you think he was primarily a glider?  His glide ratio isn't as good
as that of a pigeon; it isn't all that bad either, but I
wouldn't expect him to make a living at it, just like a pigeon isn't
good enough at to make a living with it.

  >> If it could cascade, then it would have also had many of the
advantages > of high aspect ratio wings.

  >Yes, good point...

And wouldn't have been draggy.  But cascaded tails are speculative.  No
evidence either way.

  >>Which was my point too.  They're increasing the fineness ratio (and

  >But does apply to a running take-off, as well as after the critter is

Well, yes it does.  Air is air, whether you're in flight or not.
However, I tend to doubt that archie did running takeoffs,
though I think he was probably capable of it.  I do think he likely did
running landings, as I've mentioned before.

 > Gawds, so do I!  But you may need to wash your car more often
though.  :-)

I once thought about what it would be like to stand under a flock of
northropi if they had a metabolism like a cormorant
(consuming 15% of body weight per day).  Yuck.  Thank goodness they
didn't need that much energy.

  >Actually, what I meant by my remark that "the world is a much better
  >for it" - .............. is that it's allowed birds to exploit an
enormous number of ecological niches.
  >......opposed to ........ "_Archaeopteryx_-grade" avians.  The latter
did (apparently) persist until the end of the
  >Cretaceous (_Rahonavis_); but they were outnumbered (and outcompeted)
by the upstart pygostylians.

Since they lasted till the end of the Cretaceous, it may not have been
the pygostylians what done um in.