Re: pteros have lift-off

[jrc <jrccea@bellsouth.net>]

This might be a good place to mention that unlike many birds, pterosaurs
have a relatively low rate of climb and climb out at a shallow angle.
Something that I've not seen elucidated by the bipedal/quadrupedal launch
controversy is that bipedal launch for most pterosaurs whether by leaping or
running would orient the flapping plane in a direction that would primarily
tend to decelerate the animal reducing its flight speed without providing
substantial lift, while the quad launch would orient the flapping plane in a
direction that would both lift and accelerate the animal forward, increasing
its flight speed.  I think the bipedal launch scenarios would need to
explain that discrepancy.

The wingspan estimates that I've seen for Istiodactylus suggest a span on
the loose order of 4.8 to 5 meters or thereabouts.  If built similarly to
ornithocheirds (I haven't read much about Istiodactylus, so am presently
ignorant of their relationships) that would imply a mass on the loose order
of 18 to 20 Kg or thereabouts. If so, a 4.8 meter span Qsp would probably be
3 to 5 Kg heavier.  I do note that Istiodactylus is reported as having a
deeply curved deltopectoral crest.  If one surmises that that phrasing means
that it is shaped something like the Quetz and Hatz dp crests, it should be
noted that the dp crest shape is important to increasing quad launch power
in more robust ptersoaurs.

Dave says, "Wing finger, nearly three times longer relative to torso. Big
problem. It has to leap three times higher to follow the same wing opening
trajectory, whatever the lateral angle, ".

I must not be following Dave, because that statement makes no sense whatever
to me as phrased, and I see no reason why a relatively longer wingfinger
relative to the torso should imply a direct ratio to required leaping
height. What am I missing?

I also note that some seem to assume that the primary axis of the leap is
vertical and needless to say, it is not.  Pterosaurs would tend to go out
initially with both the torso and the flight angle at an average angle on
the loose order of 25 to 35 degrees from the horizon, not the zenith. After
the first downstroke, that angle would rapidly decline to approximately 3 to
5 degrees.

As an aside, I reserve comment on a 250 Kg mass for Hatz, but you aren't
likely to see a 250 Kg quetz.  A heavy one might mass somewhere around 180
Kg, and the average should be well under that, probably closer to 150 Kg.
That said, when I first started messing with pterosaurs back in the 90's, I
was seeing in the literature northropi mass estimates on the order of 75 Kg.
I soon started pressing for heavier weights than that, as did Greg Paul
about the same time.  Personally, I'm thrilled to see others now projecting
heavier weights for these animals, even when i think they are too heavy.

JimC

----- Original Message ----- 
From: "Jaime A. Headden" <qilongia@yahoo.com>
To: <dinosaur@usc.edu>
Cc: "David Peters" <davidrpeters@earthlink.net>
Sent: Sunday, January 11, 2009 8:10 AM
Subject: Re: pteros have lift-off


>  Note also here that as Jim and Mike have been saying, the feet are in
> fact of less value in thrusting in quad-launch than are the arms, which
> provide the main arm extension power. I would actually imagine
> *Istiodactylus*, and other long-arm pterosaurs like *Arthurdactylus*, to
> have a much larger thrust capability to their mass on launching than
> larger pterosaurs, and this may be ecologically important.

> Jaime A. Headden