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University of Iowa News Release


May 18, 2009

Museum of Natural History will host sloth dig event in Shenandoah May 30

The University of Iowa Museum of Natural History will bring the Ice Age to life in Shenandoah, Iowa, on Saturday, May 30 with a day of free public activities based on the nearby Tarkio Valley Ice Age sloth excavations at the Greater Shenandoah Historical Society Museum, 800 West Sheridan Ave.

The day's events, which will be held from 10 a.m. to 3 p.m., are part of the museum's 150th anniversary celebration and include the first-ever public display of the Tarkio Valley sloth toddler with bones from the adult and baby. Other activities will include a video showing footage from the site, a slide show on the history and future of the Tarkio Valley, an "artifact road show" where visitors can bring fossils and artifacts to an expert for identification (no appraisals will be given), and a hands-on activity table for children.

The Tarkio Valley Sloth Project -- an ongoing excavation of three giant Ice Age sloths called Megalonyx jeffersonii  -- recently identified a bone from a fourth sloth near the site, this one from a type of sloth never before recorded in Iowa, called Paramylodon harlani. Ice Age sloth expert Greg McDonald, the senior curator of natural history for the National Park Service's Park Museum Management Program and a consultant on the Tarkio Valley project, identified the approximately 5-inch long bone as the animal's fifth metacarpal, which once connected its wrist to its little finger, during a visit to the museum last week.

Both Paramylodon and Megalonyx were nearly elephant-sized Ice Age mammals that became extinct about 12,000 years ago. But Paramylodon sloths were equipped with broader, triangular claws for digging rather than the sharp claws of the Megalonyx, which were used for grabbing at woody vegetation like tree branches, McDonald said.

The new sloth identification came on the heels another major excavation discovery at the original site on April 25, when three more major Megalonyx bones were discovered. Holmes Semken, project leader and emeritus professor in the UI Department of Geoscience, and David Brenzel, another primary investigator for the project, identified the findings on site as a scapula (shoulder blade) from the baby sloth -- only the second recovery from this specimen -- and two rib bones from the older toddler sloth.

"Of all of the Megalonyx sites discovered, the Tarkio specimens will provide the basis for the most comprehensive analysis of sloth paleobiology and ecology of any to date," said McDonald, whose visit was made possible by a recent $20,000 National Science Foundation grant awarded to the project to complete excavation and begin more wide-ranging research on the discovery.

McDonald estimated that the approximately 110 bones recovered from the adult Megalonyx represent about 60 percent of the full skeleton, making it the second most complete of its kind. Only six other semi-complete skeletons of this species have ever been found, none of which are associated with younger animals. The older juvenile is also the second most complete of its kind, with more than 40 bones recovered. The skeletons have the added research benefit of being buried in sediments that will provide valuable environmental data about the climate and ecology during the sloths' lives.

The Tarkio Valley Sloth Project, a joint effort between the UI Museum of Natural History, Department of Geoscience and Office of the State Archaeologist with volunteers and students from across the Midwest, began in 2001 when Bob and Sonia Athen uncovered bones from Megalonyx jeffersonii in the bed of the West Tarkio Creek behind their home near Shenandoah. Soon, more bones were found on the property of the adjoining landowners, Dean and Loreta Tiemann. Both the Athens and the Tiemanns graciously agreed to permit excavation and donate the fossils of this rare species to the University of Iowa on the condition that students be involved in all aspects of the project: excavation, bone preservation and research.

For more information or a schedule of Shenandoah events, please call the Greater Shenandoah Historical Society Museum at 712-246-1669. For more information on the Museum of Natural History, please visit or call 319-335-0606.

STORY SOURCE: University of Iowa News Services, 300 Plaza Centre One, Suite 371, Iowa City, Iowa 52242-2500

MEDIA CONTACTS: Sarah Horgen, UI Museum of Natural History,, 319-335-0606; George McCrory, University News Services, 319-384-0012,; Writer: Maggie Anderson