Dan Graf tried getting DNA from dried up bits of muscle tissue on ca. 100-year old museum specimens of extinct freshwater mussel species.  He did not get much useful data, though he was able to amplify a short piece.  DNA breaks down quickly, especially with water and heat  (This is why DNA preservation in amber doesn't work-it seals water in).  If a specimen was put into ethanol 200 years ago, there's a better chance of some DNA preservation.  Dried specimens provide some hope of DNA preservation, if they dried quickly and have stayed cool and dry.

It also depends on what information you hope to get and how desperate you are.  Traces of DNA may remain a long time, but getting a sequence long enough to be useful is difficult.  Contamination is also major problem.  I would be extremely skeptical of any claim to get DNA from an old mussel shell in our lab because there's so much modern mussel DNA around the lab, for example.

    Dr. David Campbell
    Old Seashells
    University of Alabama
    Biodiversity & Systematics
    Dept. Biological Sciences
    Box 870345
    Tuscaloosa, AL  35487-0345 USA
    [log in to unmask]

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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