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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.
The week of July 6 was predicted to be sunny and apparently an ideal time for a two day excavation to recover additional remains of the baby and toddler discovered at the end of the May dig. As in the past, Evans Rental hauled the rented crawler to the site a day in advance. Will Mott arrived mid-morning with a large gas-powered pump which rapidly pumped the accumulated water from inside the levee. He estimated the capacity at about 100 gallons/minute. After the pit was ‘dry,’ Will relocated the levee protecting the previous dig north about 12 feet and then removed the muck resulting from two floods from off the floor of the excavation area. This was accomplished by 7:00 PM. Unfortunately, overnight thunderstorms produced heavy rains which lasted into the following day. While the creek did not overtop the levee, the rain was sufficient to flood the excavation and render the area inaccessible for the pump, crawler and people. More storms were predicted later in the day. The volunteers vowed to return as soon as possible after the area dried. Participants were William Mott, Lee McNair, Bill Wiechman, Aaron Last, David Brenzel and Holmes Semken.
Holmes Semken and David Brenzel, July 9, 2009.
It was susposed to be clear this afternoon but a big thunderstorm around 10:30 made the locality unworkable. We will start again as soon as it looks like we have a dry period. Sloth on, Holmes
There will be a special program featuring the Tarkio Valley sloths kicking off the 150th anniversary of the Museum of Natural History, University of Iowa during the afternoon and evening of Thursday, May 7.
First, there will be an open house in the Paleontological Repository, where the University’s paleontological collection is housed, from 3:00-5:00 PM. This is informal and you can visit as you wish. Staff will be present to answer questions. This will be held in Trowbridge Hall which is one building north of the Pentacrest (Old Capitol area) and next to the Union parking ramp.
At 5:00, our featured speaker- Greg McDonald will spend most of this time in the Museum Lab (Room 12) on the ground floor of Macbride. This show-and-tell will be for sloth volunteers, their families and their special guests only. RSVP if you plan to attend. Sarah will have name tags for you and these will get you into the Museum lab for a personal visit with Greg and to view of the bones that you have collected.
At 6:00 PM, there will be an public open house in Iowa Hall the entrance gallery (first floor) of the Museum of Natural History in Macbride Hall. Macbride is on the north east corner of the Pentacrest. Enjoy refreshments, exhibits (including a temporary exhibit on the Tarkio Valley sloths) and visit with friends. At 7:00, Greg will present ‘The Museum and the Megalonyx: A History of Great Aspirations and Sloths in Iowa’ in the auditorium of Macbride Hall. This is on the second floor. Greg has devoted his research life to Ice-Age ground sloths and associated, large, extinct mammals. He will tie this into the Tarkio Valley project. It will be exciting. You can find more about Greg and the program at http://www.news-releases.uiowa.edu/2009/April/042409sloth_talk.html
We recommend that you park in either the Iowa Memorial Union Ramp or the one just south of the Old Capitol Mall. You can find a map for the former at: http://www.uiowa.edu/~maps/m/mh1.htm. There are lots of restaurants in the block across the street from the Museum.
Pam, Sarah, Dave and Holmes especially hope that you can attend.
I found an interesting parallel to the honey locust story featured in “Sloth Music” in the central square of Granada, Nicaragua where there was a tree with seed pods that looked like those of a honey locust (the leaves are different). I asked our guide about it and he said that it was a melinche tree. He knew his stuff because he wrote the genus and species (Delonix regia) on the back of an envelope. He noted that as a child he and his friends would climb the melinches to collect the longest seed pods which invariably were at the top of the tree. They used them as swords because they liked the accompanying rattle (dinner bells!) during their games. I googled the tree and found that they are in the same family (Fabaceae) as the honey locust. Delonix is now endangered in the wild but is spread worldwide in the tropics as an ornamental tree, the Royal Poinciana. Recall that the honey locust also had a restricted range until it became a popular shade tree in North America.
Most sites list Delonix as native to Madagascar. If correct, who is the ghost that once spread its seeds? Giant lemurs (the size of a gorilla) and elephant birds (described as 10 feet tall) once inhabited the island (sub-continent). With the largest seeds being toward the top of the tree, it is unlikely that the pygmy hippo was its’ designated disperser. All large animals became extinct with human colonization and with that, a shrinking distribution for Delonix. It is clear that the living indigenous mammals, all relatively small (lemurs and tarsiers), are (were) not involved in its dispersal. Holmes
(Royal Poinciana image borrowed from)