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RE: Prehistoric Times (Tanystropheus)



-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
Fabio Marco Dalla Vecchia
Sent: Thursday, October 17, 2002 9:40 AM
To: dinosaur@usc.edu
Subject: Re: Prehistoric Times (Tanystropheus)


Just a short note, Tracy.

>>I for one do not know how Tanystropheus swum, but  I am not that sure that
the posture of the skeleton in fig 4 at p.15 (which represent a finding "as
preserved"), represents also a swimming  posture as suggested again at
p.22.  To my eyes it represents a taphonomic condition of post mortem
contraction of neck muscles/ligaments, as you can see in many long necked
vertebrates.<<

>This is a problem to say the least. But from my understanding of how post
mortem works is the animal has to dry out. The skeleton has be left out to
dry so the contracting muscles/ligaments can pull the neck/tail back. As can
be seen in many wonderfully extant and extinct animals. BUT, these are from
an aquatic environment (ocean floor) and I don't know how the animals could
dry out so post mortem can set in. If anyone can point me to references that
explain how that can happen would be great.<

>>First, I suppose you refer to the Tanystropheus specimens from the
Anisian/Ladinian Grenzbitumenzone/Besano Formation of Italy and Switzerland.
They did not deposit on the ocean floor. They deposited at the bottom of a
relatively deep (or relatively shallow, it depends on your point of view)
marine basin, but not an oceanic one (neither in the geological nor in the
geographical meaning of the word "oceanic"). Tany is associated with the
rauisuchian Ticinosuchus and the prolacertiform Macrocnemus, that were
terrestrial animals (at least the first).<<

Ok, I should have said marine, but it still in an aquatic environement.
Ticinosuchus was probably a bloat and float, and Macrocnemus? Hmmm...naris
dorsally placed, hmmm....yea I've thought of that one also...

>>Second, maceration in hypersaline solutions or hot water could also
produce
the typical arching of dried carcasses. I do not have direct experience of
that, I read it somewhere, I do not remember where. Also floating causes an
arching of the carcass (see Schaefer, 1972).<<

Do you remember which publication so I can narrow it down more? Thanks.

<<Now, if I'm correct and it is a snap shot of how the animal moved, then
the
animal would have had to have died in the position (which I can't explain).
IF the animal sank to the bottom then somehow moved into that position,
would there be ripples in the mud to show that the animal did move? Don't
know.>>

>>Currents are always present, also in closed, oxygen-depleted basins. Water
is never completely still. Ripples form easily in sand, but it is much more
difficult to form them in mud, because it is more cohesive (i.e., grains do
not move). Thus, the absence of ripples in the muddy bottom of the
S.Giorgio/Besano basin does not mean that weak current were absent.<<

Thanks.

Cheers,
Fabio
------------------------------

Fabio M. Dalla Vecchia, PhD
Museo Paleontologico Cittadino
Via Valentinis 134
I-34074 Monfalcone
ITALY
http://www.fante.speleo.it



Tracy L. Ford
P. O. Box 1171
Poway Ca  92074