Re: Conway's Nyctosaurus Restoration or Introducing the Bennett Prize!

["James R. Cunningham" <jrccea@bellsouth.net>]

Chris Bennett wrote:

> I have been dismayed that so many have been so quick to recosntruct a
> membrane between the two rami of the crest of Nyctosaurus.  I noted in the
> paper that there was no evidence of a membrane between the rami, and that
> includes no evidence in the structure of the rami themselves to suggest that
> there was a membrane.

Chris is absolutely correct.  Which is why I keep repeating the phrase
"IF the crest supported a membrane".  I do believe that the 'what if'
question is valid, since demonstrating that a membraned crest could not
serve as a sail while skimming in ground effect would be useful
information (it is obvious to the casual observer that a non-membraned
crest couldn't serve that function). Since the dimensions of the bony
crest fall squarely within the range needed to support a functional
membrane and is consistent with estimates of the early Turonian mean
windfield in the vicinity of the fossil sites, I think the concept
deserves further study.  I do not yet have a professional opinion (in my
own profession, not paleontology) about the actual presence or absence
of such a membrane.  My personal feeling is starting to lean strongly
toward the likely presence of a membrane, but that is a far cry from
professing that one exists.

> There are also no specimens of pterosaurs
> that show any evidecne of a membrane supported by a crest--my interpretation
> of the crest of the Tapejara specimen is one of incomplete ossificaiton of
> the crest and prezservation of the soft tissue covering of a developing
> crest, rather than one of a membrane supported by anterior and posteiror
> parts of the crest.

There is a possibility that a solid Tapejara crest could serve as a
crab-claw sail.  I haven't attempted to do those calculations yet, but
Chris makes a good point (as always).

> Conway reconstructed the nyctosaurs skimming with their lower jaws in the
> water.  I assume this is an adaptation of the Thalassodromeus interpretation
> applied to Nyctosaurus.

It isn't.  It's actually an adaptation of the suggested position for
Quetzalcoatlus, but with different neck positioning and extensibility. 
The depth of jaw submergence was chosen as that suitable for resisting
the sail sideforce at normal cruising speed in ground effect and water
track velocity (not the same).

> I and some other
> pterosaur workers have some real problems with the skimmer interpretation of
> Thalassodromeus--I think the mandible is not nearly as laterally compressed
> as it should have been if it were to be a skimmer, I fear cavitation,

A valid fear, and one fairly easily addressed with a water tunnel.  The
Nyct lower mandible shape was projected from dorsal and ventral views
and seems to be appropriate for use as a sideforce generator if
submergence is limited to approximately  the distal 10 cm.  However, jaw
submergence is not dependable as a full-time sideforce generator because
of chop, and consequently for dependability an equivalent sideforce
would need to be generatable with a wingtip or other mechanism. 
Preliminarily, that appears to be possible.  Also, average water track
velocity doesn't appear to be great enough to result in a jaw cavitation
problem (ain't finished those calcs yet).


> I see the ocean as nothing like the glass smooth ponds and lagoons where 
> skimmers
> fish, etc.

Quite so.  I suspect that no matter how they made their living, KJ1 and
KJ2 lived and died considerably closer to the west coast and that
prevailing winds and surface currents drifted them to their final
resting place.  They were found very close to the projected center of
the gyre, and the prevailing winds are predicted to have been from an
average of about 250-260 degrees.

>  However, ignoring all those problems the mandible of Nyctosaurus
> is not laterally compressed at all, and it has nothing like any of hte
> speciallizations seen in Black Skimmers.

Again, true (I haven't seen the actual specimens, but trust Chris'
measurements in that regard).  But the shape appears to be adequate for
the purpose, and skimming can't be rejected based solely (sp??) on
shape.  In the sail-glide skimming hypothesis, the lower mandible should
not be considered as the primary sideforce generator.

> Turning to the question of sailing nyctosaurs, although I have the utmost
> respect of Jim Cunningham's command of aerodynamics I distrust a lot of
> mathematical modelling because such modelling is only as good as the
> assumptions upon which it is based.

And I have equal respect for Chris.  When he says to doubt something, I
have a strong tendency to doubt it.  For example, on unrelated matters
he's convinced me of the unliklihood of pteroid tendons and has me
equivocating about a sesimoid located in the socket near the top front
of the lateral distal syncarpal.

> .....Sailboats, sailboards, land yachts, and ice
> boats all rely on sails to drive their forward motion in much the same way
> that Jim calculates that Nyctosaurus could have used its cranial jib to
> drive its forward motion, however, Nyctosaurus differs from sailboats,
> sailboards, land yachts, and ice boats in two importnat ways.  All of them
> are in contact with a dense substrate that prevents them from moving
> sideways in responce to aerodynamic force on their sail.

Quite so.

> Nyctosaurus would have nothing to keep it from blowing sideways.

Not quite so.  We see three or four ways that the animal could have
generated an appropriate sideforce.  Three of them are not reflected in
the painting.  We are all (including John Conway) agreed that the lower
jaw can't be taken as a dependable sole sideforce generator in regions
of heavy chop.  Though it is capable in smooth water of generating an
appropriate sideforce, we agree with Chris that in chop, some other
mechanism would have to be operating, and we think we know what it is
(but I'm not ready to defend it strongly yet).

>  The second way that
> sailboats, sailboards, land yachts, and ice boats differ from Nyctosaurus is
> that they all can rely on the distrubution of weight to keep them more or
> less upright. Sailboats have ballast or a weighted keel that acts to oppose
> the aerodynamic force on the sail.  Sailboards, land yachts, ice boats and
> some sailboats rely of people hanging off hte upwind side to keep them  from
> tipping over.  Nyctosaurus could do no such thing.

Actually it likely could. There are several techniques available for
creating the righting moment with asymmetric wingloading.  As an aside,
Chris is quite right in his substrate comments, which is why Nyct could
not generate thrust at altitude (with the sole exception of the highly
unlikely sinusoidal, undulating windfield).

>  What could it possibly
> do to counter the roll effect of a jib almost the same size as one wing?  It
> could not shift its center of gravity, and it could not hang off one side.
> Perhaps Jim assumes that Nyctosaurus would unload the upwind wing, but it
> just doesn't seem likely to me.

That's one way.  wingtip loading is another, though with the obvious
moment distribution problems.  There are a couple of other ways as well,
but we are still working on them.  My whole point on this concept is
that so far, it is deserving of further study -- not that it is a proven
thing.
 
> Jim may wish to counter my problems with more calculations, but I propose a
> better solution.  I hereby announce the Bennett Prize in the spirit of the
> Kramer Prize that was to be awarded to the first person to fly a man-powered
> airplane around a closed circuit figure-8 course.  Kramer offered something
> like 5000 English Pounds and then increased it when no one won in a few
> years.  I will award the princely sum of $25.00 or 25 Euros (whichever is
> greater!) to the first person to build and successfully fly a model that
> uses a vertical sail entirely above the center of gravity to extract energy
> to drive its forward flight.

You're on!  With the minor exception that 25 bucks is a lot of money and
35 Euros is even more.  Let's make it a gourmet meal at the McDonald's
of the winner's choice.  Actually, I would have a couple of caveats. 
The sail wouldn't be expected to be absolutely vertical, and I haven't
thought of the second caveat yet.  Nor am I ready to settle on a
deadline.

> 
> Lastly, I was amused that David Peters again brought up the discolored area
> in front of the skull of KJ1.  I thought I disposed of that matter in my
> June 15 reply to two inquiries by Peters.  Perhaps Peters will believe
> Conway when HE says the slab is painted and the discolored area is nothing.

I'm with Chris and John on this one too.

Jim