Re: The Magical, Mystery Ptero

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

Jaime Headden wrote:
> 
>   Greg Paul has a new article out in _Prehistoric Times_, pre-emptorily 
> writing on the *Nyctosaurus* skim-sailing
> theory before publication of the data supporting that theory, which Jim 
> Cunningham has been loathe to spill the
> full beans on for a good reason.

It's not preemptory, and I look forward to reading what Greg has
written.  We've already made presentations on the subject at Brisbane,
at Stanford University, and have another one upcoming next month at the
Advanced Physics Conference in New Jersey.  Note that we attempt to be
careful to point out that there is presently no physical evidence of a
membrane sail on the 'mast', and it is quite possible that none exists. 
We are interested in the aero-hydrodynamic parameters and performance
issues should there be a membrane, and whether the physical structure of
the mast/boom/sail combination would have been appropriately sized to
match estimates of the weather conditions on the Western Interior Seaway
during the early to mid-Turonian.  It was.
 
> Rather than forwarding the
> theory of a sail-bearing crest, Paul describes the crest as 'a psychedelic 
> structure that gives new meaning to the
> neocreationist concept of "intelligent" design -- it looks like someone 
> designed it while on LSD.'

I would hope that what we are doing is not perceived as a theory that
the crest did support a membrane, or that we are pushing the concept
that it did.  What we are looking at is quite different, being "If the
crest did support a membrane, what might have been its effects upon the
animal and, with membrane, is the crest appropriately sized for any
useful function commensurate with the conditions present at the time?". 
Should the membraned crest concept turn out to preclude flight or
feeding, it would provide some evidence that it did not exist in life. 
So far, it appears that if the membrane existed, it would have been
quite useful.

> Paul makes an observation that is
> worth some consideration: if the animal flew, the crest must have an 
> aerodynamic component.

It is worth consideration, and the positioning of the center of lift
(with sail) is far enough aft that it is stabilizing in flight (unlike
some crests).  The aerodynamic components are indeed interesting.

> The problem with this
> is that even if the crest served a display structure, it will still be 
> aerodynamic in form,

Well yes, but the issues are rather different if there is no membrane.

>   1. 'The combination of low surface area and failure to appear until all 
> grown up suggest the crests were not
> airfoils such as rudders, but were instead display structures.' (Pg. 47.)

You can be pretty sure that they were not primarily intended as rudders
whether they supported a membrane or not.

>   I take this to mean the absence of any preservation of the "sail" as 
> implied by Jim Cunningham and John Conway.

Your phrasing is somewhat ambiguous (or maybe, ours was).  We do not
intend to imply the presence of a 'sail' on Nyctosaurus. Rather, we are
interested in investigating the properties of such a sail (if it
existed), and how it might have affected the animal.  We are finding
that it would be a distinct benefit -- but are well aware that that
cannot and should not be taken as evidence that it existed.

>  3. '[S]ails only work when the mainbody of the vessel has a substrate that 
> it can work against. Water in the case of sail boats and ships,

Almost true.  But as Ilan Kroo has pointed out, it is possible that a
sail crest could provide thrust in a substantial, sinusoidally varying
windfield without benefit of substrate.  Needless to say, in practice
such a windfield is unlikely in the extreme.

>   To counter this, I will use the example of the extant skimmer, *Rhynchops,* 
> in which this bird occassionally
> holds the tips of its wings when flying levelly into the water to stabilize 
> the water-penetrating beak. This has
> also been used to support use of the beak in larger pterosaurs, in the 
> writings of Jim Cunningham, and is likely
> used by other "skimmers" like ornithocheirids.

We have proposed the use of wingtip penetration to provide righting
moment and sideforce resistance in both Quetz and Nyctosaurus, and have
previously pointed out that the joint between PhIV-3 and PhIV-4 in Quetz
appears specially modified to handle water penetration loads.  It should
also be noted that wingtip penetration can provide side thrust
resistance and righting force to resist the heeling moment in lieu of
the lower mandible.  The beak doesn't have to be in the water for the
sail-glide skimming concept to work (though it does have to be in the
water for the 'skimming' part to work :-).

>   4. 'Also, when sailing against the wind the sail is set at an angle to the 
> direction of travel,

Of course it is.  And that angle varies with height above the water
(sail twist).  The same is true of any other sailing direction.  Note
that Nyctosaurus would be able to sail as closely to the wind as any
racing yacht, but would not be able to sail very much toward the
downwind side.

> so a pterosaur
> that tried to do this with its crest would also have to swivel its large beak 
> to the side,

Yes, but not as much as one might expect.  We've plotted yaw graphs to
explore this.  It isn't a problem.

> creating a rudder effect
> that would prevent the creature from moving in a straight line.' (Pg. 47.)

Not that much of a rudder effect. Particularly when one considers the
shape of the mandible in cross-section.  Again, it isn't severe enough
to present a problem.

> As long as the pterosaur kept its head stable and in line, a "sail" would be 
> little detriment.

It is highly unlikely that a pterosaur could always select a feeding
course that would result in its sail being 'in line'.

> See point five for more on the issue head use in water.
> 
> and a specialized upper/lower keel that stabilized
> the jaw during the snatch-n-grab method of feeding.

It appears to me that the upper/lower keel was designed to rotate the
head and neck to bring the jaw out of the water if it were to become
misaligned, moreso than being a stabilizing mechanism.

> The offset of the upper keel suggests the attitude of the head
> at max "snatch" position was pointing caudoventrally well into the water, and 
> the wings would need to be in the
> water to prevent the animal from being sideways or into the water head-long.

No, the upper keel would just swing the head and jaw clear if they
became misaligned. Which doesn't preclude the wings from being used too.

> Jim Cunningham has also
> described (and I think published) on the ability of dorsally flat-jawed 
> *Quetzalcoatlus* to surface skim, so that
> too reduces point five.

And Quetz's jaw only opens to 50 some-odd degrees.
> 
>   Paul describes *Nyctosaurus* as having lived almost entirely on the water, 
> coming to land only for breeding
> purposes, as he proposes for other marine pterosaurs.

Like Colin McHenry, I see Nyctosaurus as being a likely estuarian
feeder.  Like him, I think KJ1 and KJ2 were 'floaters' and far from
home.

> Paul supports this by alluding to the walking posture of *Nyctosaurus* being 
> difficult because of the
> absence of manual digits, but that's odd because it can still (as used by 
> Unwin) walk on the metacarpal-phalangeal
> joint of the wing digit, as Paul illustrates in the paper.

The manual digits are useful during launch, with two generally pointed
outboard to resist sliding aftward, and one aftward to resist sliding
outboard.

All the best,
JimC