Abstract

The end Cretaceous mass extinction was marked by a dramatic change in biodiversity, and the extinction of all non-avian dinosaurs. To understand the diversity of dinosaur clades prior to this event, as well as recovery by avian dinosaurs (birds), we need a better understanding of the global fossil record. However, the fossil record from southern localities, particularly southernmost (>60°S) South America, has only recently begun to be described. Discoveries from Patagonia are important to accurately assess global trends in dinosaur diversity, particularly during the latest Cretaceous before the Cretaceous/Paleogene (K/Pg) mass extinction event. Here we describe new theropod dinosaur specimens, representing both associated material and isolated elements, from Upper Cretaceous (Campanian-Maastrichtian) deposits of the Río de las Chinas Valley, Magallanes-Austral Basin, Chile. These discoveries include the southern-most known occurrences of several theropod clades outside of Antarctica, including megaraptorids, unenlagiines, enantiornithines and ornithurines. Notably, these remains provide much needed time-constrained records of smaller theropods, including birds, which are less often recovered from Upper Cretaceous deposits. While fragmentary, these fossils are the first records of theropods from Chilean Patagonia, and provide insight into the distribution of avian and non-avian theropods in southern high latitude ecosystems prior to the K/Pg mass extinction event. Sampling from this region is still sparse, and more fossils from age-controlled sections are needed to accurately assess global extinction dynamics through the end Cretaceous.