Prosaurolophus, meaning “before Saurolophus,” is a genus of hadrosaurid dinosaur from the Late Cretaceous Period (75 million years ago) of North America. It is known from the remains of at least 25 individuals belonging to two species. The first specimen was discovered in 1915 by paleontologist Barnum Brown at Red Deer River in Alberta, near Steveville. It was described as a new genus in 1916, based on its similarities to the genus Saurolophus, which he had described in 1912. Saurolophus had a similar but longer and more spike-like head crest.

The type species is P. maximus. A second species, P. blackfeetensis, was described in 1992 by paleontologist Jack Horner for the Museum of the Rockies. The two species are differentiated mainly by the crest size and skull proportions. Fossils of both species have been found in the Dinosaur Park Formation in Alberta and the Two Medicine Formation in Montana.

The Dinosaur Park Formation, home to the type species, is interpreted as a low-relief setting of rivers and floodplains that become more swampy and influenced by marine conditions over time as the Western Interior Seaway transgressed westward. The climate was warmer than it is today in that region, without frost, but with wetter and drier seasons. Conifers were the dominant canopy plants of the time, with an understory of ferns and flowering plants.

P. maximus is only known from the upper part of this formation, which had more of a marine influence than the lower section. The Dinosaur Park Formation was also home to well-known dinosaurs like the horned Centrosaurus, Styracosaurus, and Chasmosaurus, fellow duckbills Gryposaurus, Corythosaurus, Lambeosaurus, and Parasaurolophus, tyrannosaurid Gorgosaurus, and armored Edmontonia and Euoplocephalus.

Prosaurolophus was a large-headed duckbilled dinosaur. The adult was about 28 feet long with a 2.9-foot-long skull. It had a small, stout, triangular crest in front of the eyes, with the crest sides being concave, forming depressions. The upper arm was relatively short. Like other hadrosaurids, the whole front of the skull was flat and broadened out to form a beak, ideal for clipping leaves and twigs. The back of the mouth contained thousands of teeth suited for grinding food to be easily swallowed.

The two species of Prosaurolophus are differentiated by details of the crest.

Prosaurolophus was an herbivore, eating plants. Its teeth were packed into dental batteries and were continually replaced throughout life. It would have fed from the ground up to about 13 feet. Although mainly a quadrupedal dinosaur, it could also stand on two legs.

Bone bed evidence has shown that this genus lived in groups at least part of the year. In its social setting, the dinosaur had several potential methods for display, including the bony facial crest, or a possible nasal diverticula. The postulated diverticula would have taken the form of inflatable soft tissue sacs housed in the deep excavations flanking the crest and elongate holes for the nostrils. Such sacs could be used for visual or auditory signals.