The Rhabdodontidae (Dinosauria, Ornithischia), an enigmatic dinosaur group endemic to the Late Cretaceous European Archipelago

The Rhabdodontidae was one of the most important dinosaur groups inhabiting the Late Cretaceous European Archipelago. Currently, the clade comprises nine species within six genera, which have been found in southern France, northern Spain, eastern Austria, western Hungary and western Romania, ranging from the Santonian to the late Maastrichtian. Phylogenetic analyses consistently place the Rhabdodontidae at the very base of the iguanodontian radiation, whereas the in-group relationships of rhabdodontids are relatively poorly understood; nevertheless, the clade seems to have had a rather complicated biogeographical history. Generally, rhabdodontids were small- to medium-sized, probably habitually bipedal herbivores, characterised by a rather stocky build and a comparatively large, triangular skull. Several lines of evidence suggest that they were presumably gregarious animals, as well as selective browsers that fed on fibrous plants and occupied different ecological niches than sympatric herbivorous dinosaur clades. Moreover, the sympatry of at least two rhabdodontid taxa was rather common and can be explained, at least in some instances, by niche partitioning. While rhabdodontids disappeared prior to the K/Pg extinction event in Western Europe, they survived close to the end of the Cretaceous in Eastern Europe, where they were amongst the last non-avian dinosaurs still present before the end of the Cretaceous. In this paper, we provide an overview of the rhabdodontid taxonomic history, diversity, phylogenetic relationships and palaeobiogeographic history, as well as palaeoecology and extinction. In addition, we also highlight still open questions on each of these topics and suggest potential future research directions.