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

Re: Prehistoric Times (Tanystropheus)



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