Redescription of the skull of 'Saurolophus osborni' Brown 1912 (Ornithischia: Hadrosauridae)

A detailed redescription of the skull of the hadrosaurine 'Saurolophus osborni' based on the three known specimens of this taxon, elucidates for the first time several important aspects of the cranial morphology. Details of the braincase, palate, and nasal crest that were either missed or disputed by previous authors are clarified. The nasal crest is buttressed caudally and caudolaterally by elongations of the frontals and prefrontals, respectively. The unique morphology of the frontals and prefrontals permit differentiation of 'S. osborni' from other hadrosaurs. 'S. osborni' can be differentiated from 'Saurolophus angustirostris' by a relatively shorter frontal contribution to the nasal crest, a relatively straight premaxilla in lateral view, a weakly upturned oral margin of the premaxilla, and the absence of a vertical sulcus on the prootic above cranial nerve V. A reassessment of the phylogenetic affinities of 'S. osborni', exclusive of 'S. angustirostris', suggests it is most closely related to the Laurasian taxa 'Prosaurolophus' and 'Kerberosaurus'.