Multiple observations on the preservation of dinosaur tracks in a lacustrine to fluvial setting (Late Cretaceous, El Molino Formation; Parque Nacional de Toro Toro, Bolivia)

The Upper Cretaceous El Molino Formation (Maastrichtian) in Bolivia is well known for its extensive dinosaur track record. However, the palaeogeographic variability of the dinosaur track record and thus changes in dinosaur biodiversity at the northwestern margin of Gondwana are not yet fully investigated. We therefore aim to study the Nuevo Camino section in the Toro Toro National Park, Bolivia in order to unravel the site-specific track record in relation to ambient depositional, environmental and preservational conditions. Drone-derived orthophotographs, outline drawings and false colour maps in combination with detailed sedimentological logging and thin section analysis of hand relevant specimens complement our approach. We found the Lower Member of the El Molino Formation being made up of 55 m of mixed carbonate-siliciclastic sedimentary rocks. Within this sequence 30 different track layers were identified. They include heavily trampled surfaces as well as surfaces with individual tracks and trackways of medium-sized theropods (FL< 35 cm) and small ankylosaurid trackmakers (FL