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Re: Nyctosaurus dorsal frill



----- Original Message -----
From: "David Peters" <davidrpeters@earthlink.net>
To: <cbennett@bridgeport.edu>; "dinosaur list" <dinosaur@usc.edu>
Sent: Tuesday, March 25, 2003 8:07 AM
Subject: re: Nyctosaurus dorsal frill


> > OK, I'll bite.  Can you point me to a particular specimen of
> > Nyctosaurus that exhibits the frill?
>
> It's the Field Museum specimen. But it's the worst example of the lot (=
> hardest to see) and I can only recognize it because I'm looking for a
> match to all the other pterosaurs and I've boosted the contrast to the
> max. If you can do the same, and you know what to look for, you'll see
> it. Without the experience of seeing better examples (=like learning to
> read x-rays) I'm afraid you'll have negative results.
>
> David Peters


The Field Museum specimen was my second choice--my first was the Fort Hays
specimen; however, it makes little difference.  It is not surprising that
the frill on the Nyctosaurus is that hardest to see of all the examples
Peters has found, because the Nyctosaurus is preserved in Niobrara Chalk.  I
had the pleasure of at least partially preparing hundreds of specimens of
Pteranodon from the Niobrara Chalk for my dissertation, and so I think that
I know a little about the Chalk.  Specimens are typically found as some part
is eroding out of an exposure, the chalk is prepared away so as to ascertain
the extent of the specimen, and then an appropriate size slab of chalk
containing the specimen is removed (nowadays with the aid of a plaster
jacket).  Subsequent preparation involves scraping or air-abrading away the
chalk covering the specimen.  The chalk is never split as a shale or
limestone is, and the preparation almost always goes below the actual
bedding plane of the specimen.  As a result the bones appear to be sitting
on a smooth (or slightly tooled) chalk surface of the slab, rather than
being embedded in the slab.  As an example look at Williston's (1903, On the
osteology of Nyctosaurus (Nyctodactylus)...) Plate XL of the Field Museum
specimen--the chalk of the bedding plane has been removed and all the bones
are sitting on top of the plane of the slab.  Given that the actual bedding
plane of the specimen has been removed during preparation it is remarkable
that Peters has been able to find traces of soft tissues.

Chris


S. Christopher Bennett, Ph.D.
Assistant Professor of Basic Sciences
College of Chiropractic
University of Bridgeport
Bridgeport, CT 06601-2449