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Diatryma Track (Re: New Palaeoichnological papers)




From: majid mirzaie <majid_mirat@yahoo.com>
To: vrtpaleo@usc.edu
Date: Wed, 29 Sep 2004 09:36:53 -0700 (PDT)
Subject: New Palaeoichnological papers
Message-ID: <20040929163653.91778.qmail@web21205.mail.yahoo.com>

<massive snippage>

> A Probable Diatryma Track from
> the Eocene of Washington: An
> Intriguing Case of Controversy
> and Skepticism  pp. 341 - 347.
> John Patterson and Martin Lockley 


See also:  Lockley, M. and A. P. Hunt. _Dinosaur Tracks_. page 262.

<sigh>  It is hard for me to understand why this specimen is still
actively discussed in the paleo-ich' community!  I saw the slab in
question about 10-13 years ago, not long after it had been collected. 
The slab was stored in the Burke Museum basement in the same room where I
was doing some visiting research on another fossil, so I would
occasionally glance over at the slab that was supported on a wooden
pallet.  During one of my breaks, I broke out my magnifying glass, and
put a floodlight on the markings.  The "footprint" had hammer (chisel?)
marks around it (and, I assert, also within the crescent-shaped "toenail"
imprints).  The "footprint" also had that eery appearance of being TOO
well-preserved, particularly in the toe area.  The Puget Group matrix
comprising the specimen is a laminated very fine grained sandstone to
siltstone.  I saw no evidence of soft sediment deformation around the
margins of the impression.  The undisturbed laminations are clearly
visible along its sides.  In the middle of the "footprint", I could see a
couple roughly circular contour lines that represent planar laminations
oriented almost perfectly horizontally.  Why isn't the sediment along the
margins of the impression deformed by the downward movement of the foot? 
And why isn't the sediment directly under the foot deformed by the weight
of the animal?  To me, it appeared as though the impression was formed by
spalling and river erosion.  The "toes" and "toenail" impressions are
harder to explain as an effect of spalling, but the undeformed
laminations in those areas raised a red flag.  The distal margins of the
"toes" cut straight down through the matrix.  There are no rounded edges
of matrix around the "toenails", only sharp, nearly 90-degree margins. 
In fact, many of the margins elsewhere on the imprint are subangular to
angular.  In contrast, rounded edges are common features of autheticated
fossil tracks.  I admit that I only looked at the specimen for about 15
minutes, but that was enough time for me to shrug my shoulders and
scratch my head.  Later, noting the above features and noting a few more
features, _Diatryma_ expert Allison Andors came to (roughly) the same
conclusions as I did (that it probably isn't a track).

Unfortunately, a bunch of shiney stabilizer was slathered over the slab,
so it was difficult to check for other characteristics of the matrix.

I haven't yet read the most recent article (see above).  Hopefully,
Patterson (the collector) and Lockley are providing new information.  But
from my limited knowledge of the Puget Group seds at the state park
locality, I don't believe that other vertebrate tracks have been found at
that particular spot.  The collection site is also a popular locality for
salmon fisherman, so if anything out of the ordinary is exposed along the
banks, one can be sure that word would eventually get out.

I am no expert on paleo-foot-squish marks.  The slab is certainly
interesting, no doubt about that!  But as far as interpretating it as a
fossil track, weeeelllll......

<pb>
--









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