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Re: Prehistoric Times (Tanystropheus, rigor mortis)




I wrote:

>>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.<<

Tracy replied:

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.

And aspidel added:

Or the dead _Tanystropheus_ has been swept along by the come-and-go of the
sea waves, if it was near a beach, that's why the fossil has this strange
position.
Just an idea passing by...


Please be so patient and let me add my last (at least for today) toughts on this:

Without dismissing other possibilities I would recall that surely ligament contraction in dead animals occurs mainly in drier areas, but rigor mortis (RM), i. e. contraction of *muscles* after death, may take place in water as well as on land. RM happens (recalling to memory good old teachings of anatomy) because death stops production of ATP which is (VERY ROUGHLY SPEAKING) responsable of muscle de-contraction by pushing off Calcium ions from muscle protein (? tropomyosine ?) receptors.
When there is no more ATP, nothing pushes off the Calcium and muscles stay contracted. RM normally does not produce odd, too contorted postures if the antagonist muscles are balanced, because all become contracted . However if epaxial muscles were more developed, bigger etc. than hypaxial ones, it is feasible that they may induce some deformation in posture with their contraction.
If the epaxial muscles in the neck of Tanystropheus were more developed than hypaxial ones, since these latter may have been in part replaced by the rib "bundles"- that can't contract-, this may explain why we found all these advanced prolacertiforms (i. e. Tany., Macrocnemus, Langobardisaurus, Cosesaurus and, correct me if I'm wrong, Tanytrachelos) with the neck sharply bent or even curled backwards.
Does it sound feasible to you?


Cheers
                                                Silvio Renesto




_
"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

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