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Re: Slightly off topic & Skippy's guts



Adam wrote:

>    Hi Dino-List,   Can anyone tell me any good web-sites that cover
>>synapsids/therapsids? I've tried the usual search engines, but only get
>course  >summaries or mailing list posts - can anyone help?   On topic: Is
>there a >verdict amongst this list's  subscribers about the latest hoopla
>over >_Scipionyx_ ? I've been trying to  follow the threads on this, but
>subject >titles aren't always a good guide as to  content. Personally I
>can't see any >liver in the photos I've seen - could it be  another case
>like >_Sinosauropteryx's_ diaphragm, or whatever the last claim was?  Any
>>taphonomists looked at it under those UV lamps? Could it be a chemical
>effect >that's unrelated to the anatomy?   Adam  

I have not seen any of the photos nor the Science article yet, but the play
of colours seen under UV is probably the result of phosphate, calcite, plus
or minus iron and some other elements in trace amounts.  Soft tissues,
especially the liver and intestines, would be the sites of intense decay,
which would reduce the local pH to levels which would start a chemical
cascade, the result of which would be phosphate and calcite precipitation
in and on tissues.  Phosphate tends to precipitate at sites of the most
intense decay (i.e. lowest pH), calcite tends to precipitate on top of the
phosphate (ppt of phosphate removes dissolved phosphate from pore fluids,
dissolved phosphate inhibits calcite ppt, so calcite ppt has to wait until
dissolved phosphate is removed) and at sites of less intense decay (higher
pH).  So you tend to get a core of phosphate, commoly surrounded by
calcite, then a ring extending around this core, composed of calcite and
sundy elements (usually iron).

See <http://members.tripod.com/~Cambrian/index.html> for examples and
colours generated by calcite ppt. over tissues.

<http://members.tripod.com/~Cambrian/EmuBay> and
<http://members.tripod.com/~Cambrian/Myoscolex>for examples and colours
generated by phosphatised muscle tissue.

However, this cascade needs some decay to initiate it.  It is therefore,
highly unlikely that the organs would remain essentially intact or, more
importantly, _in situ_ during the initial phase of decay.

Another problem, if this is the mode of preservation, is that precipitation
occurs only on the surface of the tissues.  Mineralisation is not
pervasive.  Thus, the final configuration is affected by subsequent
(inevitable) decay and collapse of the organs, resulting in significant
distortion.  I doubt that this type of preservation will preserve
sufficiant information to support the claims made.  However, I repeat that
I haven't seen the paper yet.

Chris


cnedin@geology.adelaide.edu.au                  nedin@ediacara.org
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Many say it was a mistake to come down from the trees, some say
the move out of the oceans was a bad idea. Me, I say the stiffening
of the notochord in the Cambrian was where it all went wrong.
It was all downhill from there.