Article: Telmatosaurus transsylvanicus from the Late Cretaceous of Romania: the most basal hadrosaurid dinosaur

The hadrosaurid dinosaur Telmatosaurus transsylvanicus from the Late Cretaceous of the Hateg region of Romania is redescribed and its phylogenetic position among hadrosaurids and successive sister-taxa is evaluated. Hadrosauridae is defined and diagnosed as a monophyletic group on the basis of twelve of the best-known genera and species previously referred to this higher taxon. T. transsylvanicus lacks a number of features (among them, narrow mandibular condyle of the quadrate, narrow dentary teeth, single large carina on dentary teeth) that diagnose remaining members of Hadrosauridae. As a consequence, our study indicates that T. transsylvanicus is the most basal of known hadrosaurids. The late Maastrichtian age of T. transsylvanicus suggests that this species was an evolutionary relict, isolated from its sister taxon (all remaining hadrosaurids) for at least fifteen million years. The geographical distribution of T. transsylvanicus, across an archipelago of European islands at the end of the Cretaceous, may well account for such an evolutionary relationship.