PALAIOS, 2012, v. 27, p. 725–737 Research Article DOI: 10.2110/palo.2012.p12-006r EMPIRICAL DETERMINATION OF PHYSICAL CONTROLS ON MEGAFAUNAL FOOTPRINT FORMATION THROUGH NEOICHNOLOGICAL EXPERIMENTS WITH ELEPHANTS BRIAN F. PLATT, 1,2 * STEPHEN T. HASIOTIS, 1 and DANIEL R. HIRMAS 3 1 Department of Geology, University of Kansas, Lindley Hall, 1475 Jayhawk Blvd., Room 120, Lawrence, Kansas, 66045-7594, USA, bfplatt @ ku.edu, hasiotis @ ku.edu; 2 Kansas Geological Survey, 1930 Constant Ave., Lawrence, Kansas, 66047-3726; 3 Department of Geography, University of Kansas, Lindley Hall, 1475 Jayhawk Blvd., Room 415, Lawrence, Kansas, 66045-7613, USA, hirmas @ ku.edu ABSTRACT We performed a series of neoichnological experiments with elephants to investigate the relationship between the various factors involved in controlling megafaunal footprint formation. Our ultimate goal was to provide a means to calculate original sedimentary properties of fossil- footprint–bearing siliciclastic rocks, especially those containing sauropod dinosaur tracks. Previous semiquantitative and model-based research identified multiple variables that influence footprint creation and preservation, but no rigorous, empirically based models have been constructed. We conducted track-making trials with experimental sediments and one adult female African elephant (Loxodonta africana) and one adult female Asian elephant (Elephas maximus) in a zoo setting. Data collected included track dimensions, sediment particle size distribution, sediment bulk density (r b ), volumetric water content of the sediment (h v ), and trackmaker walking velocity (v) and weight. We performed multiple regression analysis with a backward elimination technique to obtain the following relationship: V n ~0:812h v 2 {26:4h v {157r b {20:5vz518 where V n is track volume normalized by track length, measured in cm 2 , h v is in percent, r b is measured in g/cm 3 , and v is measured in m/s. We demonstrate the utility of this equation by calculating the original moisture content of sauropod-track–bearing siltstone and sandstone beds in the Upper Jurassic Morrison Formation. Original water content values are extremely useful for paleoenvironmental and paleohydrological interpretations of sediments and paleosols. Furthermore, paleoclimate studies can benefit greatly from original soil moisture values calculated from megafaunal footprints associated with paleosols. INTRODUCTION The purpose of this study is to conduct neoichnological experiments with elephants to quantify the relationship between physical variables involved in megafaunal footprint formation and morphology. The ultimate goal of this research is to enable calculations of ancient sediment and soil properties for fossil-footprint–bearing siliciclastic sedimentary rocks. The impetus for this study was a body of research on deep sauropod dinosaur tracks and interpretations of the conditions responsible for their preservation (e.g., Hasiotis, 2002, 2004; Jennings et al., 2006; Platt and Hasiotis, 2006). There are many examples of relatively large, deep footprints that have been attributed to dinosaurs (e.g., Engelmann and Hasiotis, 1999; Gatesy et al., 1999; Nadon, 2001; Gatesy, 2003; Jones and Gustason, 2006; Eberth et al., 2010) and mammals (e.g., Laporte and Behrensmeyer, 1980; Loope, 1986; Allen, 1997; Ashley and Liutkus, 2002), including proboscideans (Scrivner and Bottjer, 1986; Roberts et al., 2008). Lockley (1986) outlined specific uses of fossil dinosaur tracks for interpreting paleoenvironments and original media (5substrate) conditions, but an empirical neoichnological study of megafaunal track formation has, to our knowledge, never before been attempted. Approaches that interpret physicochemical controls on track formation include field-based observations of modern tracks in natural sediments (Laporte and Behrensmeyer, 1980; Cohen et al., 1991; Genise et al., 2009; Marty et al., 2009; Scott et al., 2010), experiments with controlled media and live trackmakers (Brand, 1996; Gatesy et al., 1999; Mila `n, 2006; Mila ` n and Bromley, 2006), laboratory experiments with controlled sediments and artificial indenters (Allen, 1989, 1997; Gingras and Pemberton, 2000; Schaub et al., 2000; Manning, 2004; Jackson et al., 2009, 2010; Falkingham et al., 2010; Scott et al., 2010), cross-sectional and structural interpretations of fossil footprints (Loope, 1986; Mila ` n et al., 2004; Loope, 2006; Platt and Hasiotis, 2006; Graversen et al., 2007), and finite-element analysis (Margetts et al., 2006; Falkingham et al., 2009, 2010, 2011a, 2011b). Footprint formation can be viewed in terms of sediment or soil compaction (e.g., Manning, 2004; Falkingham et al., 2010), which has received considerable attention in the engineering and agricultural literature because of construction specifications (Lambe and Whitman, 1969; Hillel, 1980; Lee and Salgado, 2005) and soil issues arising from livestock trampling and heavy machinery operation on arable land (Knoll and Hopkins, 1959; Hillel, 1980; Warren et al., 1986; Russell et al., 2001; Pietola et al., 2005). Experimental determinations of soil compaction in engineering and agriculture focus on applied pressure and do not discuss the dimensions of traces left behind by the indenter; Walker et al. (2005) is a notable exception. The relatively simple, circular and elliptical shapes of the soles of elephant feet (Weissengruber et al., 2006) are ideal for an empirical trackmaking study because the effects of complex edge shapes on media penetration (e.g., Falkingham et al., 2010) are minimized. Elephant trackmaking behavior is also a good analog for that of extinct proboscideans, other large mammals (e.g., rhinoceroses, hippopotami, titanotheres), and sauropod dinosaurs because of anatomical similar- ities related to graviportal locomotion—movement enabled by physical adaptations for transporting a large body mass over terrestrial settings (e.g., Sikes, 1971; Coombs, 1975; Gallup, 1989; Bonnan, 2003; Carrano, 2005; Miller et al., 2008). We take advantage of this literature by applying our results to published data from fossil sauropod tracks. METHODS AND MATERIALS Tracemakers and Facilities Trackmaking trials were conducted at the Topeka Zoological Park, Topeka, Kansas, United States, with one female African elephant (Loxodonta africana) named Tembo, and one female Asian elephant (Elephas maximus) named Sunda. Tembo was wild caught in Kenya in 1973, has been at the Topeka Zoo since 1976, has an estimated birth year of 1971 (Olson, 2011), and has a mass of ,4200 kg. Sunda was * Corresponding author. Published Online: November 2012 Copyright G 2012, SEPM (Society for Sedimentary Geology) 0883-1351/12/0027-0725/$3.00