Excavation of an extraordinary find, a relatively complete adult ice-age giant ground sloth (Megalonyx jeffersonii) associated with two juveniles from the Tarkio Valley in southwest Iowa, is now complete. The recent discovery of a Harlan?s ground sloth (Paramylodon harlani) metacarpal on a gravel bar immediately downstream from the Tarkio locality added a new dimension to the project: there are two entirely different forms of ground sloth in close stratigraphic proximity of one another. The PI requests funds to undertake an AMS C14 dating of these two distinctly different species (and genera) of ground sloth to verify their ages relative to one another. Determining the ages of these two different genera of Pleistocene ground sloths is crucial for understanding their paleobiology and paleoecology. The AMS C14 date is a high risk ? high reward activity in that it is uncertain that its application to long bone medullary cavity materials will be successful; if successful, the new methodology will be transformative for this method. The University of Iowa Plesitocene research program is extraordinary from the standpoint of its outreach to the lay public, undergraduate and graduate students and will continue as a component of this EAGER proposal.
Discovery The 1993 flood redirected the course of the West Tarkio Creek, southwestern Iowa, into ice-age deposits previously buried for 12,000 years. Almost a decade later, when drought reduced the Tarkio to unusually shallow and clear conditions, the landowner discovered a thigh bone of Jefferson’s giant ground sloth (Megalonyx jeffersonii), a rare ice-age species, in the stream bed. This specimen was especially significant, not only because of its rarity, but because continued search revealed numerous other elements of the sloth. The sloth was in danger of loss to erosion and clearly required salvage. It was donated to the University of Iowa under the proviso that it be properly excavated and that students were involved in all aspects of the excavation and research. Unfortunately, the locality was a logistical nightmare because the bones were either submerged in the bed of the stream or under 24 feet of overburden. Heavy equipment would be required to both redirect the course of the creek and remove a substantial amount of overburden as excavation progressed. NSF funding provided needed earth moving equipment for site preparation and supported preliminary laboratory analyses to develop the Tarkio excavation into a world class educational and research endeavor. Excavation was strictly a volunteer effort with participants paying their own expenses. Excavation Physically, the excavation was an outstanding success and resulted in the recovery of the most complete adult Jefferson’s giant ground sloth known along with two contemporaneous juveniles (known colloquially as the toddler and baby), one of which is tied for the most complete specimen, truly a unique family unit. The remains were buried in an incised channel, created by stream straightening, which drains a 170 km2 catchment basin. Five cm of rain upstream raises the water 2.5 m or more over the locality. Flooding was frequent and the excavation of the Tarkio Valley sloth always occurred behind a series of levees to relocate the West Tarkio Creek into previously excavated areas. Upon completion, excavation covered a 20 X 25 m area in the valley bottom and extended at least three meters away from the outermost recovered specimen to insure complete recovery. Each element has been professionally photographed and these will be posted on the Museum of Natural History and Paleontology Repository websites with existing excavation photographs: www.uiowa.edu/~nathist/slothsite/index.html Field Observations The death site was clearly in a low energy, backwater environment. The skeletons were not articulated but both large and small bones were intermingled indicating minimal loss to erosion after death. The Tarkio adult is the first in which both posterior and anterior elements are available for comparison but the juveniles are primarily known from chest elements. The animals fell on their left side at death because bones from the left side were better preserved (buried more quickly) than those on the right. The presence of dry fracture with carnivore and rodent gnawing also documents that the remains were exposed to weathering before burial. Juvenile remains were recovered in distinct clusters suggesting that they were transported short distances as skin adhered bundles, possibly rafting. The adult was not fullygrown but was suffering from arthritis. Research The reach component of the project included DNA, stable isotope, paleobotanical, sedimentological, pathological, radiocarbon. optical thermoluminescence, soil micromorphology, rare earth element, and soil chemistry analysis. These revealed the sloths lived over 100,000 years ago in an intergrlacial, forested environment and probably reflect a family unit. Public Participation Traveling Trunks. A traveling trunk, featuring plastic copies of the sloth and comparable human bones, has been developed for the 'Geo2Go' teaching trunk series prepared in collaboration between the UI Museum of Natural History, Department of Earth and Environmental Sciences-Paleontology Repository, Iowa State Archaeologist and the Iowa Geological and Water Survey with support from the Department of Radiology, College of Medicine and the Rapid Prototyping Laboratory, College of Engineering. The Pleistocene and its giant ice-age mammals are a natural for this series. All are designed for public use in classrooms (K-12), museums, nature centers and other outreach venues. The Ice-Age trunks focus on demonstrating scientific deduction via comparing the humans and sloth skeletons to interpret biomechanics and ice-age climates, ecology, and extinction of North America's ice-age giants. For instance, a sloth claw may be used for defense, digging, or reaching high-hanging fruit. Conversely, it is not constructed for tool use or clutching. Volunteers. Volunteers ranged in age from 14 to mid-80, and included students, farmers, physicians, home makers, dental assistants, mechanics, and teachers (all levels). College majors included computer science, communication, anthropology, pre-med, psychology, geology, fine arts, MFA, museum studies, physics, sociology, art education and engineers. Exhibits. The Museum of Natural history, University of Iowa, has a life-size reconstruction of Jefferson’s giant ground sloth and a display of sloth remains available for public viewing in the Iowa Hall gallery.
