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The first hadrosauroid remains from the Santonian Milk River Formation are described here and include a right frontal, partial left jugal, right surangular, fragmentary right quadrate, dentary, teeth, and postcranial elements. When considered within a phylogenetic context, this material indicates the presence in this formation of at least one non-lambeosaurine hadrosaurid, possibly with close affinities to the approximately contemporaneous Lophorhothon from southeastern North America. The material described here represents the only geographic occurrence of Santonian hadrosaurids from the northern part of the Western Interior Basin. Given the putative occurrence of latitudinally arrayed northern and southern dinosaur “provinces” on Laramidia during the late Campanian, the Milk River Formation fauna has implications for understanding the origin of the faunal differentiation that occurred later in the Cretaceous. |
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