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Re: Solnhofen Taphonomy

>The hypocline (the boundary between hypersaline water and
>normal/freshwater) is very fluid (groan!). It is affected by water
>temperature, climate - atmospheric conditions (amount of evaporation),
>freshwater/normal saline water imput -, currents (mixing) etc. Thus, during
>times of high evaporation and low water imput, the hypocline can rise to
>very shallow depths (possibly even reaching the surface? - although that is
>a bit extreme). Thus organisms entering the lagoon during these times have
>a high preservational potential (as represented by excellently preserved
>specimens?). During times of lessened evaporation and increased water
>input, the hypocline will sink to lower depths resulting in shoddy
>preservation - or possibly no preservation at all - of organisms entering
>the lagoon from above.

        OK, I'll buy that as an acceptable solution.  Perhaps that explains
the differences in preservation of some of the specimens of, for example,
_Archaeopteryx_ -- gorgeous preservation in the Berlin and Eichastatt
specimens (preserved perhaps during shallow hypoclines), and much worse,
more disarticulated specimens like the Maxburg and London specimens, with
deeper hypoclines.  Maybe it would even explain the deaths of some of the
pelagic marine orgaisms washed over the lagoonal barriers, such as the
floating crinoids.

>A fluctuating hypocline, plus attendant anoxia, has been invoked to explain
>the mass death and excellent preservation of fish from the Cretaceous
>Santanna Formation in Brazil. The fish from this deposit have muscle tissue
>preserved down to the cellular level (Martill 1988). Also pterosaur wing
>membranes have been preserved (Martill & Unwin 1989).

        OK -- but, as far as I know, no one's proposed such mass death
scenarios for the Solnhofen.

Jerry D. Harris
Schuler Museum of Paleontology
Southern Methodist University
        (Compuserve:  73132,3372)

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"South American Animals and Their Lice"

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