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Fwd: Re: Gizzard stone scratches & furrows



From Oliver Wings...

From: "Oliver Wings" <oliver.wings@web.de>
Reply-To: vrtpaleo@usc.edu
To: "Vert-Paleo Mailing List" <vrtpaleo@usc.edu>
CC: "Forum on trace fossils" <SKOLITHOS@LISTSERV.REDIRIS.ES>, bandbj@bitstream.net
Subject: Re: Gizzard stone scratches & furrows
Date: Wed, 19 Nov 2003 18:36:43 +0100


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 subject).
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,
Oliver

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.)
Wissenschaftlicher Volontaer
Niedersaechsisches Landesmuseum Hannover - Naturkundeabteilung
Willy-Brandt-Allee 5
D - 30169 Hannover
Germany
Phone: +49 (0)511 9807830
Fax:    +49 (0)511 9807880
E-mail:  oliver.wings@web.de

Official website: http://www.nlmh.de
Private websites: http://go.to/gastrolith
                http://www.dinosaurhunter.org

Current research topics:
Gastroliths, Bone Diagenesis, Vertebrate Taphonomy



*********** REPLY SEPARATOR  ***********

On 18.11.2003 at 08:49 Mickey Rowe wrote:

>Anybody with a research interest in gastroliths should consider
>contacting Dr. Robert Johnson. He tried to write to the dinosaur list
>(I've enclosed his message below -- the image he tried to send was
>"truncated" out by the listprocessor, so if you want to see pictures
>you'll have to contact him). His message was bounced to me since he's
>not a subscriber to the dinosaur list (and I presume not VRTPaleo
>either); I wrote to him and asked about the motivation for his
>message. The first paragraph in the enclosed messages below is part
>of his response on that point:
>
>
>------- Start of forwarded message -------
>Date: Tue, 11 Nov 2003 09:35:58 -0600
>From: Robert Johnson <bandbj@bitstream.net>
>To: Mickey Rowe <rowe@psych.ucsb.edu>
>Subject: Re: Gizzard stone scratches & furrows
>
>Having only recently grasped the significance of the types of scratches
>that I described and now have photographed, it seemed like a good idea to
>get the knowledge out to others who are interested in gastroliths. In a
>casual search, I found only one other person (an english graduate student,
>I think) who was interested in the scratches, and I sent to him a couple of
>my stones. I might be interested in doing a formal paper on them , but not
>alone because this is not my field. My primary interest is in
>paleoclimatology and climate-change mechanisms. See:
><secretsoftheiceages.com> ...The role of the Mediterranean Sea in climate
>change.
> R.G. Johnson
>
>> ------- Start of forwarded message -------
>> Date: Sun, 09 Nov 2003 10:59:41 -0600
>> From: Robert Johnson <bandbj@bitstream.net>
>> To: dinosaur@usc.edu
>> Subject: Gizzard stone scratches & furrows
>>
>> I have a collection of polished quartz-type stones found in the
>> surface lag deposits of central Wyoming. Many of them have
>> characteristic scratches that could only have been made in the gizzard
>> of an animal, probably a plant-eating dinosaur. The scratches are
>> typically 1-3 mm long and often are visibly tapered at each end where
>> the squeeze on the hard mineral grain began and ended as it was caught
>> between two sliding and rotating surfaces of the stones themselves.
>> Under a scanning electron microscope, the scratches consist of long rows
>> of individual pits, probably made by stick-slip or rotational action of
>> the hard grain (probably garnet or zircon) when compressed between
>> neighboring stones.
>> Not all polished quartz stones have visible scratches, as would
>> be expected depending on the diet of the animal using the stones.
>> Eating plants pulled up by the roots would result in the swallowing of
>> sand grains , whereas an animal feeding on upper foliage would not
>> likely ingest sand grains. Quartz sand does not scratch quartz stones,
>> but even those stones without scratches often show the characteristic
>> rounding of fractured edges or holes that would have resulted from
>> constant wear of quartz on quartz as the stones did their job of keeping
>> the plant material stirred up and exposed to the digestive juices.
>> I attach a microscopic picture of one of my better examples of
>> the dense pattern of criss-crossing scratches. The scale is about 1.5
>> mm from top to bottom of the picture. I can conceive of no natural
>> process outside a gizzard that would create these scratches. Wear by
>> the action of stream flow or windblown sand produces random impact pits,
>> not rows of scratches with a pattern that is often tapered at each end.
>> Robert G. Johnson, Adjunct professor, University of Minnesota
>>
>> ------- End of forwarded message -------
>------- End of forwarded message -------
>
>--
>Mickey Rowe (rowe@psych.ucsb.edu)





End tranmission.

Jordan Mallon

Undergraduate Student, Carleton University
Vertebrate Paleontology & Paleoecology

Paleoart website: http://www.geocities.com/paleoportfolio/
AIM: jslice mallon

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