Preliminary studies of a new dinosaur track locality from the Candeleros Formation (Cenomanian, Upper Cretaceous), Neuquén Basin, Argentina

Abstract

A new Upper Cretaceous (Cenomanian) dinosaur track locality ¨El Chocón Medio¨ from northwesternPatagonia, Argentina, is reported here. More than 30 true tracks (concave epireliefs) were recognizedin fine-grained sandstone beds, interpreted as floodplain deposits. The only distinct trackway consistof six deep and medium-sized tridactyl tracks poorly preserved with distinct metatarsal impressions(about 50 cm long and 20 cm wide). This trackway does not reflect changes in footprint featuressuch as track length, depth, pace and height of displacement rims, suggesting that the consistencyof the substrate was homogenous along the complete distance. About 20 m from this trackway,several deeper and large tridactyl tracks (30 to 40 cm in length) with very pronounced rims havebeen identified. They are positioned close to each other and show different orientations, accordinglywere considered as isolated tracks. They are poorly preserved and lack anatomical features, makingit difficult to determine a theropod or ornithopod affinity. Finally, in the underlying bed (10 cm be-low) several subcircular (70 cm in diameter) and crescent-shaped (50 cm in width) natural cast tracks(pes-manus) of sauropods were documented. At least three sauropod pes from the same side (leftor right) where arranged in an incomplete trackway, so the type of gauge could not be determined.Preliminarily, considering the similar morphology and heteropody, these tracks can be assigned tocf. Sauropodichnus giganteus Calvo, 1991, from the same unit and tracksite proximity. The presenttrack assemblage shows that this site was repeatedly visited by different groups of dinosaurs.