SGER: Excavation, Osteology and DNA Determination of the Tarkio Valley, Iowa, Ground Sloths

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Excavation, Osteology and DNA Determination of the Tarkio Valley, Iowa, Ground Sloths Holmes A. Semken, Jr. PIAbstract. An extraordinary adult ice-age giant ground sloth, Megalonyx jeffersonii, was discovered in a southwest Iowa stream bed in 2001 following a major flood. Subsequent excavations, possible only during periods of reduced flow, have produced 104 elements (about 55 percent) of the discovery skeleton. This specimen now represents the second most complete Jefferson?s giant ground sloth known. The scientific value of this adult specimen was compounded tremendously by the subsequent discovery of two juveniles (41 bones at present) of different ages partially intermingled with the adult. This is the first direct association of an adult Megalonyx with possible offspring. The pond-like depositional unit containing the sloth remains also contains plant macrofossils, pollen, mollusks as well as limited numbers of micro-vertebrates. These will provide information on the immediate and regional environments at the time of death. Superior preservation of the sloth remains suggests that isotope analyses of the skeletal elements should provide dietary information about these enigmatic creatures as well as temperature values around the time of death. The probability of good isotopic analyses is supported by elemental maps of an adult tooth. Carbon has been determined as present in the dentition so it is possible that DNA is also is present. If present, sex, family relationships and absolute age of the specimens in radiocarbon years may be determined. The site, latest Pleistocene in age based on stratigraphic position, is located a known distance from the glacial front (Des Moines lobe) and should provide insight on the climatic tolerances of this wide-ranging taxon at an ecological extreme. It is clear that breeding occurred near the ice front. It also appears that the sloth group lived close to the end-Pleistocene mega-mammal extinction event and may assist in the search for an explanation. The Tarkio Valley biotic association offers an unparalleled opportunity to enhance our knowledge of both the physiology and paleoecology of Megalonyx. A team of scholars with specialties in palynology, stable isotopes, plant macrofossils, microvertebrates, molecular biology, archaeology and Quaternary stratigraphy is eager to supervise students in the total analysis of the association. However, before a comprehensive analysis of the specimens and their paleoenvironmental associations, can be conducted, it is necessary to (1) ensure recovery all remaining skeletal elements, (2) complete a skeletal inventory and osteological analysis of each sloth and (3) ascertain if comparative DNA analyses of the Tarkio specimens is possible. Part of the find is located under eight meters of overburden on the north bank of the Tarkio Valley, others are just below the stream bed and the bone bed extends under a four meter slump block to the south. The north bank has been cleared but heavy equipment is required to expose the stream bed and uncover the bone-bearing deposits under the south bank. Once total excavation is accomplished, a complete element inventory, osteological analysis and bone distribution map will be prepared to provide the basic data necessary for all future investigations. The final phase of this exploratory effort at the Tarkio Valley site is to determine if sufficient DNA is preserved to establish relationships between individual sloths at the site. Completion of these three phases will then permit the Tarkio Valley locality to be one of the most comprehensively examined ice-age large mammal associations on record. This discovery has excited thousands of people regionally via a web site, traveling exhibits, lectures and volunteer participation. An outreach Intern will provide immediate updates and better coordinate all of these activities. Activities can be reviewed at: www.uiowa.edu/~nathist/Site/sloth/index.html