The Magical, Mystery Ptero

["Jaime A. Headden" <qilongia@yahoo.com>]

  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.

  Paul, G. S. 2003. The magical, mystery pterosaur *Nyctosaurus gracilis*.
_Prehistoric Times_ 62:46-47.

  Paul describes the possible life history of *Nyctosaurus,* using
Bennett's recently described new specimens as *N. gracilis,* though
Bennett refrained from using a specific epithet in his own paper. 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.' He also describes the crest as 'like ...
flattened deer antlers.' (Both quotes from pg. 46.) It is a peculiar study
on the living function of a VERY peculiar, flattened, aerodynamically
controlled crest. Paul makes an observation that is worth some
consideration: if the animal flew, the crest must have an aerodynamic
component. The problem with this is that even if the crest served a
display structure, it will still be aerodynamic in form, or the animal was
landbound, so evidence against an aerodynamic function for a display
function will be effectively nil, as any aerodynamic structure will be
exapted for in a flying animal, whatever the original function, and thus
people would be prone to see aerodynamic first, display second. Cranial
crests likely served both functions, but the surface area is widely
variable. Anyway....

  Paul lists several reasons why the crest is more likely to be a display
structure than an aerodynamic one:

  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.)

  This has a lot to do with the idea that there are posteriorly crestless
skulls of *Nyctosaurus,* which Bennett states is unknown, so the idea that
there are crestless skulls cannot be supported and thus cannot support
point one.

  2. '[L]ack of anatomical evidence' (pg. 46) and (earlier, pg. 47)
'[T]heir crisp edges differ from the amorphous rims of the crests of
pterosaurs in which keratin sheaths greatly expand the area of the crest.'

  I take this to mean the absence of any preservation of the "sail" as
implied by Jim Cunningham and John Conway. The problem with this is that
while this my offer that the bony crest did not have bone fade into the
keratin, as occurs only in *Tapejara,* it would not prevent pterosaurs
like *Germanodactylus* and *Austriadactylus* from bearing what is
generally agreed to have a bone-based keratin-sheathed cranial crest. This
occurs in *Gnathosaurus,* as well, where the bony margin is well-formed
and not too irregular, but highly rugose and ridged. The rugosity is not
known in the beaks of pterosaurs (commonly held to bear keratin sheaths)
or *Tapejara,* but is known in *Tupuxuara* and *Thalassodromeus,* and more
primitive, "rhamphorhynchoid" pterosaur crests. So the conclusions of
features of the bony crest as bearing keratin are not clear-cut, as birds
and turtles both will show "unfinished" and very porous bone beneath
keratin beaks, and some show complete, smooth "finished" bone.

  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, the
ground or ice in case of sail????? [what are terms for sail driven ice
runners and land racers?].'

  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.

  4. 'Also, when sailing against the wind the sail is set at an angle to
the direction of travel, so a pterosaur that tried to do this with its
crest would also have to swivel its large beak to the side, creating a
rudder effect that would prevent the creature from moving in a straight
line.' (Pg. 47.)

  This might be the point, but Paul does not argue the absence of a
head-turning rudder effect in other crested pterosaurs, from
*Tropeognathus* to *Pteranodon,* *Austriadactylus* to *Tupuxuara* or the
more impressively crested *Thalassodromeus.* So these animals needed to
fixed-headed in flight, or be incapable of head-turning during feeding.
The black skimmer likely does not turn its head in feeding, and the
wing-tips in water insures stability. As long as the pterosaur kept its
head stable and in line, a "sail" would be little detriment. See point
five for more on the issue head use in water.

  5. Paul notes the length of the jaws in *Nyctosaurus* are even in
length, in *Thalassodromeus* where the lower jaw's tip is mediolaterally
compressed with a dorsal keel, and an allusion to the skimmer,
*Pteranodon* with a longer upper jaw than lower with inferred surface
water feeding as in dipping, separate from skimmers.

  Would like to note that ornithocheirids like *Anhanguera* show various
modifications to skimming including a lower jaw that could open to almost
90 degrees to the upper jaw, and a specialized upper/lower keel that
stabilized the jaw during the snatch-n-grab method of feeding. 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. *Pteranodon* shows the same modifications of the
jaw joint, suggesting great usage of the jaw at full gape with a bony
"stop" to prevent the jaw opening further, likely to brace it during
maximum gape. Thus it would seem length of the lower jaw, and likely shape
of the jaw tip, would have little bearing on actual feeding habits as long
as the wings weren't too deeply water-lodged or the animal spilled to the
side or forward and became destabilized. 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.

  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. This appears to be odd, because aside from the
kingfisher *Halcyon,* there are no marine birds which would dare nest on
open sea, and the loons prefer near shore mats to lay their eggs on. The
sea otter also rears its young on protected mats of seaweed, but not open
water, and there are few exceptions to other large living animals that
live entirely on open water. *Nyctosaurus* has fully capable quadrupedal
posture, even is walking was awkward, so I cannot see the possibilities of
living on land being difficult. 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.

  Paul notes that the crest of *Nyctosaurus,* which apparently appeared
relatively late in ontogeny given the less ossified surface of KJ2 versus
KJ1, appears to show an "adult"-appearing full crest, implying that
display is the most likely conclusion for the "antlers," rather than a
sail. But in fact, the conclusion away from a display via keratin or
skin-based crest coverage over the struts does not seem to hold positive
evidence on Paul's side, so the argument appears to favor only a
display-related crest function, and this seems to be the sole support on
the matter. Paul also appears to contradict himself by saying 'It is less
likely that the crestless specimens were the girls and the crested ones
the boys, although this cannot be ruled out until more specimens are
sampled.' (pg. 46) but then goes on to describe a scene which is also
illustrated of an immature, *Pteranodon*-like stubby-crested skulled
female watching a full-crested, antlered male displaying, without any
hesitation on remarking which are male or female. As above and noted by
Bennett, crestless specimens with a complete occiput are unknown, so this
conclusion as to the shape or presence of the crest in females is not
tenable, especially given such absence of crestless specimens of other
species of crested pterosaurs. It seems unreasonable to assume we have
recovered ONLY males from the Santana and Crato Formations of crested
species.

  Note the change in email has occured -- again -- my Yahoo! issues seem
to be resolved for the most part as my POP mail has been ... acting up.

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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