[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Gizzard stone scratches & furrows



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)