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Date: | Tue, 23 Dec 2003 22:41:12 -0500 |
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A few of the mollusks also had partially calcite shells back then, especially some of the pterioid bivalves. Various taxa today also have calcite. There are also some rock units (including some around Cinncinnati) that have the original aragonite shells replaced with calcite or silica in a way that preserves fine details, even including internal structure of the shell. However, the majority of well-preserved shells that look sort of molluscan in those rocks are actually brachiopods.
The oldest known examples of preserved aragonite come from a bit southeast from Cinncinnati, in the Pennsylvanian of eastern Kentucky. However, deposits as young as Pleistocene may have the aragonitic shells entirely lost.
Dr. David Campbell
Old Seashells
University of Alabama
Biodiversity & Systematics
Dept. Biological Sciences
Box 870345
Tuscaloosa, AL 35487-0345 USA
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That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa
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