Authors: Tim Treiber, Zoltán Csiki-Sava, Aaron J. Ebner, Felix J. Augustin
Abstract: Ankylosaurs are a widespread but rare constituent of the latest Cretaceous dinosaur faunas of Europe. In the famous Upper Cretaceous continental deposits of the Haţeg Basin (Romania), ankylosaurs were first reported over 100 years ago and since then have been found in various localities across the wider Transylvanian area; nevertheless, they still represent an uncommon faunal component. We report here the first evidence of the group from the fossil-rich Maastrichtian ‘Pui Beds’ of the eastern Haţeg Basin. The specimen, an isolated scapula, can be confidently assigned to Struthiosaurus sp. based on thorough morphological comparisons. Among the scapulae referred to Struthiosaurus from France, Austria and Romania, the Pui scapula is most similar to S. transylvanicus from roughly coeval strata of the central Haţeg Basin. Besides reporting this new specimen, we provide a detailed overview of the ankylosaur fossil record from Transylvania and discuss its implications for the palaeoecology and evolution of ankylosaurs in the eastern part of the Late Cretaceous European Archipelago. Contrary to previous hypotheses, ankylosaurs do not seem to have been environmentally segregated from the more common sympatric herbivorous dinosaur clades (rhabdodontids, titanosaurs, hadrosauroids) on Haţeg Island, but instead were widely distributed albeit numerically subordinate members of the palaeofauna(s). According to our updated overview, ankylosaurs first appeared in the Transylvanian Basin and only later show up in the Haţeg Basin. Finally, in stark contrast to the situation in the western Ibero-Armorican Landmass, ankylosaurs were present throughout the entire Maastrichtian in the Transylvanian area