Revision of the status of 'Saurolophus' (Hadrosauridae) from California, USA

Abstract

The occurrence of 'Saurolophus' from the Moreno Formation (late Maastrichtian) of California is investigated and an incomplete, poorly preserved, skull (LACM/CIT 2852) is described. The skull lacks the braincase (including the frontals) and much of the nasals, and the preserved portions are crushed or plastically deformed, which makes anatomical interpretations difficult. A preserved midline fragment of the conjoined nasals suggests that it lacked a gryposaur-like "Roman nose", but the nature of the crest, if present, is impossible to determine with certainty. A phylogenetic analysis places this specimen as either the sister taxon of 'Saurolophus' or as the sister taxon to a clade comprising 'Edmontosaurus' and 'Anatotitan'. There is no compelling morphological evidence to support the previous assignment of LACM/CIT 2852 to 'Saurolophus' rather than to 'Edmontosaurus', and its poor preservation prevents positive assignment to any taxon below Hadrosaurinae indet. Given its geographic setting and morphological uncertainties, it is also possible that this specimen represents a separate taxon, but more material is needed to clarify the identity of the Moreno hadrosaurine. LACM/CIT 2852 does, however, provide evidence that Maastrichtian hadrosaurines ranged west of the Sierra Nevada magmatic arc, in an area where dinosaur diversity is poorly known.