First hadrosauroid record from Petreşti-Arini (Transylvanian Basin, Romania; Upper Cretaceous) and its implications for the evolution of the Hațeg Island vertebrate faunas

The uppermost Cretaceous continental deposits of Transylvania (western Romania) represent one of the most iconic sources for fossil vertebrates from the Late Cretaceous European Archipelago. Among the numerous uppermost Cretaceous sites known from the Transylvanian Basin, Petreşti-Arini is one of the most important, due to its geological age and preservation of an unusual transitional near-shore environment. Current knowledge of the local vertebrate assemblage included many of the groups typically present in the Upper Cretaceous of Romania but not the hadrosauroids or titanosaurs. In this report, we describe a right humerus of a hadrosauroid discovered at Petreşti-Arini in the lower part of the Sebeş Formation. The humerus can be confidently assigned to a basal hadrosauroid based on its long and robust deltopectoral crest (45% of the humeral length) that is nevertheless shorter than in derived members of the clade (in which the deltopectoral crest is > 55% of humeral length). The specimen represents the first record of hadrosauroids from Petreşti-Arini, dated to around the latest Campanian, making it not only the stratigraphically oldest record of hadrosauroids in the Transylvanian Basin but also one of their earliest well-constrained occurrences across Haţeg Island overall. The specimen refines previous scenarios and gives a better age constraint on the arrival of hadrosauroids to Haţeg Island, documenting their introduction to this area before the end of the Campanian. Additionally, it might imply some sort of paleoenvironmental control over hadrosauroid distribution on Haţeg Island.