EMPIRICAL DETERMINATION OF PHYSICAL CONTROLS ON MEGAFAUNAL FOOTPRINT FORMATION THROUGH NEOICHNOLOGICAL EXPERIMENTS WITH ELEPHANTS

• Published in: Palaios 2012-10, Vol.27 (10), p.725-737
• Main Authors: PLATT, BRIAN F, HASIOTIS, STEPHEN T, HIRMAS, DANIEL R
• Format: Article
• Language: English
• Subjects: Archosauria; Bighorn Basin; bulk density; Chordata; Diapsida; Dinosaurs; Elephantidae; Elephantoidea; Elephants; Elephas; Elephas maximus; Eutheria; experimental studies; Experimentation; Fossils; grain size; ichnofossils; Jurassic; living taxa; Locomotion; Loxodonta africana; Mammalia; Mesozoic; modern analogs; Moisture content; Morrison Formation; Paleontology; pressure; Proboscidea; regression analysis; Reptilia; Sand; Saurischia; Sauropoda; Sauropodomorpha; Sediments; statistical analysis; substrates; Tetrapoda; Theria; tracks; United States; Upper Jurassic; velocity; Vertebrata; vertebrate; Vertebrates; Walking; water; Wyoming
• ISSN: 0883-1351; 1938-5323
• DOI: 10.2110/palo.2012.p12-006r

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 (ρb), volumetric water content of the sediment (θv), and trackmaker walking velocity (v) and weight. We performed multiple regression analysis with a backward elimination technique to obtain the following relationship: where Vn is track volume normalized by track length, measured in cm2, θv is in percent, ρb is measured in g/cm3, 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.