PLoS One PLoS One Intra-trackway morphological variations due to substrate consistency: the El Frontal dinosaur tracksite (lower Cretaceous, Spain). Razzolini N.L. Vila B. Universidad de Zaragoza Castanera D. Falkingham P.L. Barco J.L. Canudo J.I. Universidad de Zaragoza Manning P.L. Galobart À. 2014 research-article