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Archae taphonomy (Was Re: FEATHERS AND POSTURE)



Dinogeorge wrote:

>In a message dated 95-10-22 15:11:38 EDT, martz@holly.ColoState.EDU (Jeffrey
>Martz) writes:
>
>>      If Archeopteryx was arboreal, what was it doing (literally) on
>>scrub islands without trees?

They weren't on the islands. Bodies were washed in by rivers, which flowed
through their habitat further inland, feeding the lagoonal system.

>Even more interesting: What was it doing sunk at the bottom of a lagoon?

Most organisms will sink after death, as they become waterlogged. A factor
keeping Archae on the bottom would have been the hypersalinity (high salt
level)  of the water. Whilst hypersaline water is more bouyant than normal
water *provided you are bouyant*, it is also harder to float up through if
you are not bouyant. The usual increase in bouyancy seen in decaying bodies
is due to gas buildup formed from the decay process. In hypersaline, low -
zero oxygen conditions decay is slowed and there is a concomitant slowdown
in the accumulation of gas. The gas can therefore dissipate before
sufficient has accumulated to cause positive bouyancy. Not only that, but
the bottom mud would have been sticky, acting like a weak glue.
The above is guesswork, but I do not think the sustained negative bouyancy
of Archae is a problem.

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.