Morphological variations in bipedal dinosaur tracks from the Aguada de Tuco tracksite, Candeleros Formation (Cenomanian, Upper Cretaceous) of northwestern Patagonia, Argentina

Abstract

New bipedal dinosaur tracks from the Aguada de Tuco tracksite of the Cenomanian Candeleros Formation (Neuquén Group, Neuquén Basin, Argentina) are reported here. These tracks are preserved in medium grain-sized sandstones from fluvial deposits in three different stratigraphic levels (Level 1-3). The Level 1 comprises deep tridactyl tracks with apparent metatarsal impressions (average length of 31 cm) preserved as true tracks and undertracks, perhaps generated due to simply sinking of the pes into a soft substrate. The Level 2 includes large tridactyl tracks (average length of 58 cm) found a few meters close to a previously studied sauropod trackway. These bipedal and quadrupedal large tracks differ in several preservational features probably due to differences in the pedal shape and substrate interaction between these trackmakers. Level 3 comprises small to large tridactyl tracks (length from 6 to 34 cm) with a broad variety of morphologies including intra-trackway variation, suggesting changes in the substrate properties, mainly moisture content, along the tracking surface. Considering that the footprints studied here are poorly preserved, they were not assigned to any particular ichnotaxon. The large tridactyl tracks were attributed to theropod trackmakers while medium and small tracks to undetermined bipedal dinosaurs. This tracksite exemplifies inter- and intra-trackways morphological variability of dinosaur tridactyl tracks controlled mainly by the substrate properties.