New sauropod tracks from the Yacoraite Formation (Maastrichtian–Danian), Valle del Tonco tracksite, Salta, northwestern Argentina

Abstract

A relative long sauropod trackway and hundreds of varied indeterminate dinosaur tracks, many of them probably related to ornitischians, were found many years ago in the Valle del Tonco tracksite (Salta, northwestern Argentina). This sauropod trackway is now described and analyzed in an updated context. Ichnological analyses were mainly conducted during fieldwork. Fossiliferous surface was mapped and digitalized in order to recognize the track shape and their distribution. The trackway-bearing surface belongs to an inverted section from the uppermost Cretaceous Caliza Amblayo Member, the lower unit of the Yacoraite Formation in this area. The sauropod trackway is moderate to poorly-preserved and includes twelve manus–pes imprint sets as convex hyporelief (natural casts). The heteropody is high and the PTR index indicates a medium category for the trackway gauge. The pes tracks, longer than wide, have subtriangular posterior edge and a general rhomboidal shape, lacking a lateral notch, and the digit-claw traces are laterally located. The manus tracks are subrounded to rectangular with at least two short, posteriorly oriented digit imprints. Their main features and preservation/weathering do not allow a precise assignment to a particular ichnotaxon. Taking into account the best-preserved Campanian–Maastrichtian sauropod pes tracks, two different general shapes can be differentiated: the Campanian Humaca shape (Bolivia) and the Maastrichtian Fumanya shape (Spain). The Valle del Tonco pes prints show similarities with the Fumanya shape. The presence of two pes track shapes in this age suggests that at least two different titanosaur feet morphology were present in the uppermost Cretaceous.