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    DNA

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    Another attempt for a direct radiocarbon date on the Tarkio Valley sloths failed.  Bob Feranec reports that the National Ocean Sciences AMS (Accelerator Mass Spectrometry) Facility at the Woods Hole Oceanographic Institution could not obtain a sufficient quantity of CO2 from the 2.5 milligram collagen sample that he collected via seven extractions from a molariform.

    Extraction on the tooth proved to be a labor intensive process to even recover a milligram. The sample, NOSAMS # 81815 labeled 10 RSF C14 005, which was adequate by weight, yielded only 1.7 micromoles of C02. When asked if sacrifice of a whole tooth would produce a date, Bob replied that we needed to recover at least 50 micromoles. This would require at least 150 extractions, would be a few months work and still probably would not generate sufficient CO2 for our purposes. He concluded,  “I think that it is not going to be a datable specimen.”

    Earlier, we had submitted a bone sample and a dental sample from the adult to the Keck Carbon Cycle Accelerator Mass Spectrometry facility at the University of California-Irvine. They could not recover enough collagen to date the specimen either. After attempts by two world class facilities, we are convinced that it is not possible to directly date sloth remains with current technology. Alternatives for direct dating are under consideration.  Pollen and seeds are in the matrix and offer radiocarbon alternatives. There is also the potential to date the sediments above and below the sloth-bearing matrix. 

     Exciting as they are, the Tarkio Valley sloths continue to be analytically evasive. 

    Sloth on. Holmes

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