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RE: Prehistoric Times (Tanystropheus)




-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
Silvio Renesto
Sent: Wednesday, October 16, 2002 7:00 AM
To: dinosaur@usc.edu
Subject: Re: Prehistoric Times (Tanystropheus)

At 14.15 16/10/02 +0200, aspidel wrote:

Well, I suppose I should comment on the comments of my article :)

> > In the prolacertiform camp, Tracy Ford presented new reconstructions of
> > the skull of Tanystropheus and provided new insight into its possible
> > lifestyle.
>There's a T. Ford's note about it, with line drawings, in Prehistoric Times
>#56 I just received today.
>
>Not easy to get PT in Italy, but fortunately a friend has a subscription,
>so I rushed at his desk to look at the new issue.
As I repeatedly posted here, I  basically agree with Tracy new
intepretation of the skull, so I have nothing to add now on this. Also the
reconstruction of the whole skeleton is nice.<<

Thanks.

>>Some concerns there are however for  other sections of the paper : at p.
15
it is written that the cervicals are 11, while at p. 22 it is written they
are 10. Err... actually they should be 12.<<

Dohhh!!! My mistake.

>>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.

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.

>>  See how the head is set off, along with the first cervicals,
from the rib bundles. some force bent the neck against the bundles and rip
off the head.<<

The body can 'stiffen' (don't ask me how) then the little buggers of the
ocean that eat dean animals can go to work and the skeleton can fall apart.

>>When swimming, undoubtedly Tanystropheus was a slow swimmer, and probably
the posterior limbs played a great role, given that the anterior ones were
reduced and with a poorly ossified carpus. The tail was not deep as in tail
propelled swimmers and mobility in its proximal third was hindered by wide
transverse processes. Haemal spines are very small and narrow in the distal
portion of the tail, not usual for a tail propelled swimmer.<<

I agree. They were slow low agile swimmers.

>>Its sauropterygian contemporaries were nothosaurs and neusticosaurs, which
had long necks and long tails. They were very good  swimmers even if quite
different from their plesiosaur successors.Nothosaurs used mainly the stout
forelimbs (not yet completely modified into paddles)  for swimming, while
neusticosaurs were propelled mainly by the long and rather deep tail with
fan-like haemal spines. The long neck of triassic sauropterygians
(placodonts excluded it's obvious)  had good lateral but little vertical
mobility (details on request, otherwise this posting becomes too long, in
short, these and the following assumptions rely on the overall vertebral
morphology  and on the orientation of  zygapophyses), the neck of
Tanystropheus had some vertical mobility but very little or no lateral
mobility.  The Tschanz idea was that of a diver with a trident (I do not
know if this is good English, I mean the long stiff stick with one or more
pointed spears) to catch fishes.
Is really a great  mistery but also a great fun wondering
about  the  possible eco-morpho-what else-types that will fit for
Tanystropheus!<<

Sure is fun to think about. Thanks for the comments.

Cheers,


Silvio Renesto

Now I got to write the next article, 'feathered theropods', the SVP and a
little on my trip...

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