Theropod, avian, pterosaur and arthropod tracks from the Latest Cretaceous of Paredon, Coahuila, northeastern Mexico, and their significance for the end-Cretaceous mass extinctiion

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Within DFG project we recently revised two unique localities that combine an unusual diversity of avian, pterosaurian and dinosaur tracks as well as trails of invertebrates, namely arthropods. These localities (Amargos, San Francisco) were discovered by us in uppermost Maastrichtian siliciclastic delta sediments of the Las Encinas Formation in the Mexican state of Coahuila, about 40 km north of Saltillo. The majority of the trackways was produced by at least five different types of birds, while trackways of azhdarchoid pterosaurs are rare and only a single footprint of a non-avian theropod was found. Our initial data therefore provide substantial evidence for a gradual decline in this area of both dinosaurs and pterosaurs and simultaneous radiation of birds prior to the end of the Cretaceous. We have evidence that the sediment containing the trackway assemblage was deposited during the very latest Maastrichtian. This is indicated by an up to 2.5 meter thick unit with abundant smectite spherules attributed to the Chicxulub impact at less than 8.5 meters distance up-section at Amargos. Sphenodiscus pleurisepta is the last ammonite at Amargos and may have crossed the K/Pg boundary into the earliest Paleocene. We here propose to discuss the scenarios above by recording the stratigraphic assignation of sediments and the turnover in tetrapods based on new K/Pg boundary sections discovered by us in the area and by the application of new methods. Furthermore, we will execute a monographic ichnopalaeontologic revision of the trackways.