Re: The Magical, Mystery Ptero

["Chris Bennett" <cbennett@bridgeport.edu>]

----- Original Message -----
From: "Jaime A. Headden" <qilongia@yahoo.com>
To: <dinosaur@usc.edu>
Sent: Thursday, October 30, 2003 1:17 AM
Subject: The Magical, Mystery Ptero


>   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.

Oh, so they're N. gracilis.  That makes things much easier for me.


>
>   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.
>


As I discussed in the paper, the Field Museum specimen of Nyctosaurus is
very well preserved with the dorsal surface of the skull exposed and clearly
does not have a crest.  Thus, it was at the time of death crestless.  The
specimen is immature and is consistent with my suggestion that the crest
developed late in ontogeny [Note that this is also the case in the Solnhofen
pterodactyloids, Pterodactylus, Germanodactylus, Ctenochasma, and
Gnathosaurus].  If the crest really was used as a sail as suggested by
Cunningham, then it would seem that the sub-adult, but still skeletally
immature, Field Museum specimen was unable to sail as fully adult
individuals could.  That would seem to me to argue against a sail function
of the crest.


>  .....
>
>   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.

Paul's confident assertion of the identities of males and females in
Pteranodon is presumably based on my identification of sexual dimorphism in
Pteranodon with large bodied and large crested males differing from the
small bodied, small crested females in pelvic morphology in addition to body
and crest size.  Sexual dimorphism has not been demonstrated in Nyctosaurus,
so it seems to me that Paul is not contradicting himself.


>  As above and noted by
> Bennett, crestless specimens with a complete occiput are unknown,

No, as noted above, a definitely crestless individual is known.  However, so
far we have not demonstrated that there were mature adults that lacked
crests or that there was a bimodal variation in crest size or morphology
that would be consistent with sexual dimorphism.  Given that we have
collected only five skulls of Nyctosaurus from the Niobrara in 130 years of
collecting, we cannot expect to demonstrate a bimodal variation in the near
future, but there is certainly the possibility that a mature non-crested or
small crested individual could be collected in the near future.


>  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.
>

Chris


S. Christopher Bennett, Ph.D.
Assistant Professor of Basic Sciences
College of Chiropractic
University of Bridgeport
Bridgeport, CT  06601