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Re: Those supercrested nyctosaurs




> I was surprised to find that in both KJ1 and KJ2 those super crests both
acted as super masts to support a very large soft crest, both fore and aft,
visible as impressions in the original matrix (now painted over I hear). In
addition, both specimens have juveniles associated and in KJ1 much of the
rest of the skeleton is impressed. The juvies also have pretty nice little
crests.
>
> This will pretty much put to rest any association of gender with crest
size or hip shape.
>
> I don't know how these crests worked aerodynamically. Suffice it to say
the sailfish is the fastest of all fish and no one (to my knowledge) has
tested the theory behind the practice. Any ref. help here would be
gratefully appreciated.


Conway, Cunningham, Gerritsen, and McHenry presented an aerodynamic model
for Nyctosaurus, based upon KJ1  & 2, at CAVEPS last year.  The presence of
a membrane was assumed, based upon the superficial similarity of the crest
to the mast and boom of a sailboard, and following an earlier suggestion by
Dino Frey.  Preliminary calculations suggested that the hypothetical
membrane could have acted like a sail during low level flight, as long as
there was contact between the animal and the water surface sufficient to
resist the leeway (sideways horizontal force) caused by the action of the
wind upon the 'sail'.  Such contact could have come from the mandibe during
skim feeding, or from e.g. the wing.  At windspeeds between 6 and 9 knots
our model is calculated to make reasonable progress over the water.  Climate
simulations of the WIB during the middle Cretaceous suggest that these
speeds would have been within the normal range of expected windspeeds.

Of course, whether or not our model has any relevance to what Nyctosaurus
was actually doing is unknown.  One problem facing any future work on this
topic is that the specimens are not in a public collection.

I'm not sure how the sailfish is relevant to our model of 'sail assisted
gliding' in Nyctosaurus.  During rapid swimming the sail on the sailfish is
retracted into a longitudinal groove that runs along the back, similar to
the recesses for the paired fins in this and other tunniforms.  See the
appropriate episode of 'The Blue Planet' for footage of this.

Cheers
Col