DIGITAL DINOSAUR TRACKING: USING GIS TO ANALYZE THE TWENTYMILE WASH DINOSAUR TRACKSITE, GRAND STAIRCASE-ESCALANTE NATIONAL MONUMENT, UTAH

Variations in paleoenvironmental conditions may alter the behavior of prehistoric animals inhabiting an area. Evidence for this type of paleobehavioral response can be seen at a dinosaur track locality in the uppermost part of the Middle Jurassic Entrada Sandstone of southern Utah. The Twentymile Wash Dinosaur Tracksite is located approximately 25 km southeast of the town of Escalante. At this site, nearly one thousand dinosaur tracks are preserved in a 16-meter thick upper sandy member that contains several track-bearing levels exposed along a 400-meter long bench. The tracks are preserved as darker sediment infillings and as alternating light and dark underprinted sand laminations. Tridactyl tracks (15 to 45 cm long) and unique sauropod tracks and traces are preserved in dozens of trackways (2 to 30 steps in length). In addition to the trackways, other behavioral evidence is expressed in horizons of multi-directional trample zones (with as many as 90 randomly placed tracks in an 80 square meter area).

In order to preserve the value of the resource and to better understand its complexities; photogrammetry, GPS, and GIS were utilized to document the Twentymile Wash Dinosaur Tracksite. Photography (at a variety of scales) and GPS coordinates were combined to produce orthorectified, digital photomosaics of the track-bearing surface. Images (viewed in a three-dimensional, softcopy photogrammetric environment) were used to produce mapped outlines of individual tracks. Calculations made automatically from the digital maps provide track size, step/stride lengths, and trackway geometry. As a result of these mapping efforts, this tracksite can be examined in a three-dimensional virtual environment. This environment allows for the visualization and analysis of tracks and trackways in a spatial and temporal context. Through the use of GIS analysis, changes in relative abundance and orientation of trackways, along with the trample zones can be correlated to stratigraphic position within the exposure. In addition, changes in trackway geometry (such as width of straddle and pace angulation) may be recorded. These variations may represent changes in use of the area, as small-scale changes in paleoenvironmental conditions occur; possibly representing seasonal, migratory, feeding, or faunal variations through time.