NEOICHNOLOGICAL EXPERIMENTS WITH MODERN ELEPHANTS TO QUANTIFY PROPERTIES OF MEGAFAUNAL FOOTPRINT FORMATION: PRELIMINARY RESULTS

We are conducting ongoing neoichnological experiments with large vertebrates at the Topeka Zoo in Topeka, Kansas, to quantify the relationship between the sedimentary and physicochemical variables in the formation of megafaunal footprints. The relationship can be applied to fossil footprints and solved for any one variable where all other variables are measurable or can be estimated. We are interested in using fossil footprints to interpret original moisture content of continental siliciclastic deposits. Previous attempts to interpret substrate- moisture conditions from fossil footprints have been only qualitative or semiquantitative. A quantifiable relationship between all variables is extremely useful for interpreting paleoenvironment, paleohydrology, and paleoclimate. Neoichnological experiments with elephant footprints can be applied to rocks and sediments that contain tracks of sauropod dinosaurs and extinct proboscidians.

Experiments are underway with one African elephant (Loxodonta africana) and one Asian elephant (Elephas maximus). Each elephant is an adult female and each weighs about 4,000 kg. The elephants walk through pits filled with experimental substrates in which the independent sedimentological variables are manipulated. The main independent variables investigated are foot pressure, animal speed, grain size, moisture content, and density of sediment. We estimate foot pressure from weights and weight distributions because this is how pressure is estimated for extinct animals. We measure footprint volume rather than footprint depth as the dependent variable because depth is affected partially by the surface area of the sole of the foot and volume accounts for this circumstance. Footprint volume is measured by water displacement of plaster casts. Preliminary results indicate a positive correlation between sediment moisture and footprint volume.

We observed also traces related to feeding, excretion, resting, and reduction of skin exposure. Oscillating striations and tight spirals are formed from swinging and grasping of food and sediment by the trunk. Urination produces craters, scours, and sediment sorting. Resting traces contain skin impression patterns correlatable to specific areas of the body. Blown and thrown sediment and water create small, shallow craters.