A new hadrosaur (Reptilia, Ornithischia) from the Upper Cretaceous Judith River Formation of Montana

The Family Hadrosauridae as commonly understood is here considered diphyletic on the basis of a cladistic analysis, and the two previously recognized subfamilies are raised to family status. The Hadrosauridae are more closely related to Iguanodon bernissartensis, whereas the Lambeosauridae are more closely related to Ouranosaurus nigeriensis. A new species of hadrosaurid, Brachylophosaurus goodwini, is named on the basis of a partial skull and skeleton collected from the Judith River Formation of north-central Montana. This species is characterized by frontal depressions and a depressed nasal arch. The posterolateral border of the nasal contributes to a portion of the anteromedial part of the orbit, a condition that may also exist in several other hadrosaur species. The specimen and the sediments from which it was collected support previous indications that the fauna and paleoenvironment of the Judith River Formation of Montana were considerably different from those of the Judith River Formation of Alberta.