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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
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.
The first 3″ core was taken upstream from the site on the southeast bluff overlooking the Tarkio, about 10 meters downstream from the northeast corner of the Athen’s property. This well produced a 40 foot core which was augmented by a five-foot, auger sample into underlying pre-Illinoian till. After completion, the rig was moved to the northwest bank of the Tarkio on the old Tiemann property (now Gary Peregrine’s farm). We started drilling about 15 feet from the north face of the sloth excavation pit, but the effort ended prematurely when the core barrel became blocked by a rock. A second core was initiated about 15 feet downstream from the first. This core extended to 35 feet and bottomed out in a sand deposit that kept refilling the hole, stopping deeper exploration. This core undoubtedly penetrated the sloth-bearing level which lies about 24 feet below the surface of the field.
Harold will describe and interpret the cores for his master’s thesis at UCM. It is believed that the Athen core sampled the valley wall of the Tarkio and that the Peregrine core penetrated valley fill deposits of the DeForest Formation. It is not clear yet if the sloth-bearing deposits are associated with the older wall deposits or the younger fill deposits. Age differences are substantial.
Before we left, Bob Athen produced his latest bone discovery. According to Greg McDonald, it appears to be the proximal end of a sloth metapodial. It is not complete though and Greg currently has the specimen to study for a potential match. The specimen came from the creek bed in the excavation area.
We have the crawler reserved for this Friday to prepare the Tarkio Valley site for a dig on Saturday. This could last into Sunday (but not likely). We will meet at the Days Inn parking lot at 7:30 on Saturday September 12 and caravan to the site. We will provide water, sunscreen and Deet. You should bring your own light tools (trowel, etc.). Dave, Will and I believe that we have dug up to the north bank excavation cleared a few years ago but that bone may still lie below one of our old levees. This area will be the target this trip. Will should have the overburden cleaned down to this level by Friday afternoon. Sloth on. Holmes
The UI Museum of Natural History received some well-deserved recognition in the May 11, 2009 issue of the Cedar Rapids Gazette. In their Homers/Gomers column, under what’s going right, The Gazette called the Museum a “NATURAL TREASURE.”
“The University of Iowa’s Museum of Natural History may be one of the state’s best-kept secrets. The museum marked its 150th year last week, and its mission as a teaching and research tool is still intact. The 1,000,000-item collection compiled by UI faculty and students during research expeditions, includes a signature giant ground sloth display from a major excavation near Shenandoah.”
Good Going Museum! (For the record, Rusty and display were constructed long before our Shenandoah discovery, but they are right about him/her being the same species.) Sloth on. Holmes.