Direct and Indirect Track Features: What Sediment Did a Dinosaur Touch?

Studies of dinosaur tracks have benefited from a distinction between true tracks and those made in subsurface layers—undertracks. However, the straightforward definition of true tracks becomes problematic when dealing with deep tracks, which often perforate or incise surface layers rather than simply distort them. Deep tracks from the Late Triassic of Greenland were made by theropods moving their feet through a volume of sediment along a complex three-dimensional trajectory. I suggest that designating different portions of the track as direct or indirect features is fruitful for reconstructing foot motion. Identifying which sedimentary grains, rather than which layers, were touched by the foot avoids dismissing deep tracks as undertracks and overlooking a valuable source of kinematic data.