The occurrence of sauropod manus-only trackways in the fossil record is poorly understood, limiting their potential for understanding loco-motor mechanics and behaviour. To elucidate possible causative mechanisms for these traces, finite-element analyses were conducted to model the indentation of substrate by the feet of Diplodocus and Brachiosaurus. Loading was accomplished by applying mass, centre of mass and foot surface area predictions to a range of substrates to model track formation. Experimental results show that when pressure differs between manus and pes, as determined by the distribution of weight and size of respective autopodia, there is a range of substrate shear strengths for which only the manus (or pes) produce enough pressure to deform the substrate, generating a track. If existing reconstructions of sauropod feet and mass distributions are correct, then different taxa will produce either manus-or pes-only trackways in specific substrates. As a result of this work, it is predicted that the occurrence of manus-or pes-only trackways may show geo-temporal correlation with the occurrence of body fossils of specific taxa. This journal is \circledC 2010 The Royal Society.