DIRECT AND PHOTOGRAMMETRIC REPLICATION OF LATEX-MOLDED TRACKWAYS FROM TOADSTOOL GEOLOGIC PARK, NORTHWESTERN NEBRASKA, U.S.A

Vertebrate tracks and trackways in the Oligocene Brule Formation at Toadstool Geologic Park in northwestern Nebraska were discovered in 1991. Beginning in 1992 the University of Nebraska State Museum's vertebrate fossil inventories of the Oglala National Grassland (Nebraska National Forest) found additional tracks. By 1995 at least 75 different sets of trackways were known from the park. Known trackmakers include mammals (likely rhinoceroses, oreodonts, entelodonts, horses, and camels) and birds, including bill-probe traces. Based on these tracks and trackways, the Nebraska National Forest designated Toadstool Geologic Park as Sensitive Site No. 55. In 1994 and 1995 workers from the University of Nebraska State Museum made 15 latex peels of some of the tracks, and documented vandalism and weathering of the trackways. The trackway peels were placed into deep storage in 1997. The peels, made of #800 liquid latex reinforced with cloth, were found to be in generally good condition after more than 10 years in storage. Our current study involves (1) photogrammetric imaging of the peels, (2) imaging of the trackways in the field, and (3) replication from the peels using urethane foam casting medium. Comparison of peel vs. present-day field topography using raster GIS methods can be used to quantify weathering of the trackways in different present-day orientations and landscape settings within the park. Upon completion, trackway replicas will be displayed and interpreted in the Eleanor Barbour Cook Museum of Geology (Chadron State College) and at other educational organizations along the "Fossil Freeway" in southwestern South Dakota and western Nebraska.