GRYPOSAURUS MONUMENTENSIS SP. NOV.

Etymology: In reference to the Grand Staircase- Escalante National Monument in southern Utah, where all referred materials of this species have been recovered.

Diagnosis: Hadrosaurids of the genus Gryposaurus possessing: anterodorsal process of maxilla seen through the external nares; subparallel anterior and posterior margins of the infratemporal fenestra; anteroposterior width of the infratemporal fenestra approximately half of the width of the orbit; predentary with large, pronged denticles; anterior portion of the dentary sharply downturned; surangular with distinct dorsal process on the median ridge of surangular; and ovoid mandibular foramen. The following suite of characters is also present: sigmoidal lateroventral margin of the maxilla; large nasal arch located near the orbits rising above the level of the frontals; narrow ‘U’-shaped posterior margin of the external naris; and squamosal raised well above the level of the skull roof. Gryposaurus monumentensis is significantly more robust than any other species of Gryposaurus . It is most similar to G. notabilis, but differs in having more steeply angled premaxillae, mediolaterally wider dentary, and generally more prominent jugal tubercle.

Holotype: RAM 6797, largely articulated skull lacking most of the right side of the skull (Figs 1, 3, 5A, 7A, B, 9, 11, 12, 13A, 14, 15).