Article: Variations in the morphology of emu (Dromaius novaehollandiae) tracks reflecting differences in walking pattern and substrate consistency: ichnotaxonomic implications
Fossil footprints appear in a variety of preservational states, each revealing a different morphology that can give rise to misidentification and misinterpretations. Comparative ichnological work was conducted using living emus (Dromaius novaehollandiae). It was clearly demonstrated that the morphological variation that occurred in footprints of the same animal, walking in the same manner, was caused by variation in substrate consistency. Dry sand substrates are unlikely to preserve any anatomical details of the foot, whereas damp sand or mud of firm consistency preserves a high level of anatomical detail. The finest anatomical details, such as skin impressions, are only preserved in firm mud or clay. In semi-fluid to fluid mud the track walls collapse, destroying the shape of the footprint. Increased speed of progression affects the shape of the footprint dramatically as the distal ends of the digits become more deeply impressed in the substrate during acceleration. Plantigrade stance adopted by the emu while feeding produces highly elongated footprints. Applying these observations to the study of fossil footprints demonstrates that great care should be paid to the original sedimentary conditions at the time of track making, as well as to the stance and gait of the trackmaker.