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FW: Gizzard stone scratches & furrows
At the request of Oliver Wings:
Dear all interested in gastroliths:
I have done quite a substantial bit of work on the identification of
gastroliths in the last four years and the results (Wings, O., in
preparation, The identification of gastroliths: potentials and limits.) will
hopefully be published next year.
The work was an integral part of my dissertation (Wings, O., in preparation,
Identification, Distribution, and Function of Gastroliths in Dinosaurs and
Extant Birds with Emphasis on Ostriches (Struthio camelus): Unpub. Ph.D.
thesis, University of Bonn.) which will be available as a pdf version for
free download in a few months. For those of you who can not wait for the
peer-reviewed papers following-up: I will post the link to the thesis pdf
file as soon as it is online.
Anyhow, I have to add some short comments:
My examinations (a lot of it with the SEM) have shown that the surface
textures of bona-fide gastroliths of extant (!) animals are very diverse and
depend on many different factors (e.g., rock type, size of particles, type
of food, contraction rate / force of gizzard, and many others). There are no
unique features in texture such as polish, pitting, or scratches at least in
the bird and croc stones (total mass is >350 kg) I have seen. Polish, for
instance, is very rare. Also, there are many different factors which might
have altered fossil gastroliths AFTER their use as gastroliths (e.g.,
sedimentational and diagenetical processes).
After what I have seen in the field and learned in my experiments -
including test arrangements of "artificial stomachs" (rock tumbler with HCl,
enzymes, and plant matter running for 6 month) - I would be very careful
stating that any surface features "could only have been made in the
gizzard". Especially if you look at samples from surface lag deposits which
might be altered by wind-blasting for several thousands of years.
Personally, I believe that the vast majority of these polished stones from
fine-grained sediments are not former gastroliths. Some reasons for this
opinion I have explained in my SVP talk last month, several other reasons
can be found in my thesis.
Nevertheless, it is definitely worth to continue research on the
identification of gastroliths if the (next) work is restricted to quartz
stones (the most common material in bona-fide and alleged gastroliths) and
similar diets (e.g., herbivores feeding on tough plant material). Over the
last years, I have gained access to many authentic fossil gastroliths
(tangasaurids, crocs, sauropods, plesiosaurs, etc. ) and far more material
from extant species (birds, crocs, pinnipeds). Unfortunately, I do not have
the time right now to include research on all of this material in my
dissertation. This is another great project for an ambitious MSc., so let me
know if you are interested...
I would also be delighted about any other collaboration in gastrolith
research (there is just a handful people worldwide working seriously on that
topic, and AFAIK I am the only one who has spent some years entirely on this
Certainly, I am interested in the photo mentioned by Dr. Robert Johnson,
especially because I believe that diagenetic movements could have caused
such "scratches consist[ing] of long rows of individual pits" too.
Cheers and best regards from Germany,
PS: I would be grateful if someone could forward this also to the dinosaur
mailing list to which I am not subscribed at the moment.
"MUTATIO SOLA PERPETUA EST!"
Oliver Wings (Dipl.-Geol.)
Niedersaechsisches Landesmuseum Hannover - Naturkundeabteilung
D - 30169 Hannover
Phone: +49 (0)511 9807830
Fax: +49 (0)511 9807880
Official website: http://www.nlmh.de
Private websites: http://go.to/gastrolith
Current research topics:
Gastroliths, Bone Diagenesis, Vertebrate Taphonomy
Thomas R. Holtz, Jr.
Department of Geology Director, Earth, Life & Time Program
University of Maryland College Park Scholars
College Park, MD 20742
Phone: 301-405-4084 Email: email@example.com
Fax (Geol): 301-314-9661 Fax (CPS-ELT): 301-405-0796