Holmes and I made a quick trip to the sloth site friday with Dr. Art Bettis, Department of Geoscience, University of Iowa.  Our goal was to collect a sand sample for optically stimulated luminescence (OSL) dating.  The radiocarbon data from the cores we collected last fall were inconclusive and hint that the sloths may be a lot older than we thought. OSL will give us the answer.   Sloth veteran Will Mott drove over from Council Bluffs to operate the bobcat and offer his usual extraordinary assistance.

Quartz sand particles  have tiny cracks and imperfections in their crystal structure that trap electrons emitted by radioactive elements in the surrounding sediment.  The longer they are buried the more electrons they trap.  Sunlight resets the “clock” so keeping the sample dark is essential.  Accuracy is about plus or minus 10-15%.  Expect a date in a couple of months. . . . Dave

Dave and I  met Dr. Art Bettis, Department of Geoscience, University of Iowa,  and Dr. Adel ‘Eddie’ Haj and his graduate assistant  Harold Ray,  Department of Biology and Earth Science, University of Central Missouri, at 8:00 AM, November 23, 2010 in Shenandoah and drove to the Tarkio Valley site to core the sloth locality with a Giddings trailer- mounted rig. AM temperatures started at 16 degrees and stayed below freezing all day. Frozen farm fields made access easy despite the previous week’s heavy rainfall.

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The radiocarbon test on the humic acid Tom Stafford, Stafford Research, Inc.,   extracted from inside the Paramylodon bone came back this week: 5434 to 5305 years before present.  We had assumed the humic acid entered the bone canal system after death but clearly there is recent contamination. We planned to do the same test on the Megalonyx astragalus but given this result have decided the money can be better spent.  Any hope of linking the Paramylodon, which was found in a gravel deposit a short distance downstream from Megalonyx site, to our trio now rests on an analysis of rare earth elements deposited immediately post mortem , or finding more bones in situ.

Tests on the Megalonyx are more hopeful– Robert Feranec, Curator of Vertebrate Paleontology, New York State Museum,  managed  to extract a small amount of collagen from a molar  while he was assisting Alex Bryk, Penn State,  with a stable isotope analysis.  Bob had to do 7 separate extractions, but he got plenty.  To his eye, the collagen “looks fine. ” It weighed about 2.5mg. That’s not a lot, but enough. An AMS radiocarbon date should be available from Woods Hole  next month. . . . Dave