Re: Prehistoric Times (Tanystropheus)

[Silvio Renesto <renesto@mailserver.unimi.it>]

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


> > 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.
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.
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.  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.
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.
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!
Cheers,

                                                Silvio


>

_
"The voice from the lake then asked "which is the strangest thing of all?"
Judisthira replied "Every day men see other men die, they see the chariots 
with the >corpses and the fires, yet they keep living as they were 
immortals, >this is the strangest thing of all"

                                                                (from 
Mahabharatha)


Silvio Renesto

Dipartimento di Scienze della Terra
Università degli Studi di Milano
Via Mangiagalli 34
I 20133 Milano
Italy
phone +39-02-50315511
fax     +39-02-50315494
e-mail:  renesto@mailserver.unimi.it
        Silvio.Renesto@unimi.it
have a look at our Triassic  website at
http://users.unimi.it/vertpal/index.htm