Diversity and faunal changes in the latest Cretaceous dinosaur communities of southwestern Europe

Characterization of macroecological patterns for latest Cretaceous dinosaur communities is essential to understand how those faunas were changing during the run-up to the Cretaceous-Paleogene extinction event, and thus the cause of the extinction. Outside of the well-studied latest Cretaceous dinosaurs of North America, southwestern Europe (France, Spain and Portugal) preserves one of the richest end-Cretaceous dinosaur fossil records, as it has produced hundreds of dinosaur fossil localities. We compiled a comprehensive database of all dinosaur fossil occurrences from the uppermost Cretaceous of the Ibero-Armorican region and analyze it statistically, providing the first numerical study of the ecological and taxonomic diversities of these communities. Our study corroborates previous work that has identified a major faunal change in the latest Cretaceous terrestrial vertebrate assemblages, and places this event around the C31r-C31n reversal, in the early late Maastrichtian (c. 69 Ma). Significant differences in ecological diversity metrics (dominance, Shannon and Simpson) characterize the pre- and post-turnover assemblages. The turnover event, therefore, did not only lead to a taxonomic replacement but also important reorganizations in the structure of dinosaur communities. Herbivorous dinosaurs suffered the most dramatic alterations across the turnover, in terms of relative dominances, by shifting their contributions within the communities (hadrosauroids replacing titanosaurids as the dominant taxon in the medium-to large-bodied herbivore niche) or even disappearing (rhabdodontids and nodosaurids). The carnivores apparently maintained similar relative abundances before and after the turnover, and the relative proportions between carnivorous and herbivorous taxa remained static through time. Further improvement of the present database might allow for the identification of new ecological patterns, and higher-resolution comparison with the North American records.