Prosaurolophus

Well-known paleontologist Barnum Brown recovered a duckbill skull in 1915 for the American Museum of Natural History (AMNH 5836) from the Red Deer River of Alberta, near Steveville. He described the specimen in 1916 as a new genus, Prosaurolophus. Brown's choice of name comes from a comparison to the genus Saurolophus, which he had described in 1912. Saurolophus had a similar but longer and more spike-like head crest. The skull had a damaged muzzle and was inadvertently reconstructed too long, but better remains were soon found that showed the true shape; one is a nearly complete skeleton and skull, described by William Parks in 1924. Twenty to twenty-five individuals are known for this species, including seven skulls with at least some of the rest of the skeleton. Horner differentiated the two species by details of the crest. He interpreted P. blackfeetensis as having a steeper, taller face than P. maximus, with the crest migrating backward toward the eyes during growth. More recent studies have regarded the differences as insufficient to support two species. ==Description==

Prosaurolophus was a large-headed duckbill; the most complete described specimen has a skull around long with its body size measuring in length and in body mass. It had a small, stout, triangular crest in front of the eyes; the sides of this crest were concave, forming depressions. This crest grew isometrically (i.e. without changing in proportion) throughout the lifetime of the individual, leading to speculation that the species may have had a soft tissue display structure, such inflatable nasal sacs.), in diameter, are preserved on these patches - this is similar to the condition seen in other saurolophine hadrosaurs. More uniquely, feature scales (larger, less numerous scales which are interspersed within the basement scales ==Classification==

Because of its name, Prosaurolophus is often associated with Saurolophus. However, this is contentious; some authors have found the animals to be closely related, History of classification In 1918, Lawrence Lambe revised the classifications of Hadrosauridae (then Trachodontidae). He invalidated the family name and Trachodontinae, replacing them with Hadrosauridae and Hadrosaurinae. The other subfamily in Hadrosauridae then was Saurolophinae, which included Stephanosaurus (= Lambeosaurus), Cheneosaurus, Corythosaurus, Prosaurolophus, and Saurolophus. Lambe, in 1920, split Saurolophinae and found only two genera remaining in it, Prosaurolophus, and the type genus. The previous genera were then reclassified into Stephanosaurinae or Hadrosaurinae. In 1928, Prosaurolophus was assigned to Saurolophinae by Franz Nopcsa. The group contained hadrosaurids with a "males with median horn-like protuberance on the skull" and "very numerous teeth", found by Nopsca to be Parasaurolophus, Saurolophus, and Prosaurolophus. In 1954, Charles Sternberg reevaluated the genera in Hadrosauridae, invoking the probability that Saurolophinae should be sunk into Hadrosaurinae. This greatly changed the classifications of the family, as the "saurolophines" were kept separate because of their supposedly "footed" ischium. Sternberg identified that the "footed" ischium assigned to Saurolophus was not found with the holotype, and was only assigned to it because of the location of the find. Also, he noted that William Parks (1924) found a complete skeleton of Prosaurolophus clearly showing an "unfooted" ischium, which Sternberg realized meant that it was unlikely that Saurolophus possessed a "footed" ischium. Sternberg's reevaluation led to the abandonment of Saurolophinae. }} In 2001, Prosaurolophus was studied with other hadrosaurids by Wagner. The genus, along with Corythosaurus and Maiasaura, were considered by Wagner to be synonymous with Saurolophus, Hypacrosaurus and Brachylophosaurus respectively. Prosaurolophus maximus was reassigned to Saurolophus as S. maximus. The same year however, Prosaurolophus was found to be distinct from Saurolophus, in an analysis of Hu et al. Their analysis was unique from any of the time, and they recovered Prosaurolophus in Saurolophinae, with Saurolophus, Lophorhothon, Tsintaosaurus, Jaxartosaurus, and Kritosaurus. No other analysis has recovered this group of dinosaurs. Horner et al. (2004) also recovered a different phylogeny of Saurolophinae. Prosaurolophus was, for the first time, recovered separate from Saurolophus, in fact not even closely related. Prosaurolophus was found in a group with Brachylophosaurus, Maiasaura, Grpyosaurus, and Edmontosaurus, while Saurolophus was grouped with Naashoibitosaurus (=Kritosaurus) and "Kritosaurus" australis. The Prosaurolophus-Saurolophus clade has been a problematic grouping when trying to place among hadrosaurines. Many skull features are similar to Edmontosaurus, while other are closer to Gryposaurus, so the group has been classified as close to both. However, the clade might be closer to Edmontosaurus, as the features are more numerous uniting them. ==Paleobiology==

As a hadrosaurid, Prosaurolophus would have been a large herbivore, eating plants with a sophisticated skull that permitted a grinding motion analogous to chewing. Its teeth were continually replaced and packed into dental batteries that contained hundreds of teeth, only a relative handful of which were in use at any time. Plant material would have been cropped by its broad beak, and held in the jaws by a cheek-like structure. Feeding would have been from the ground up to around 4 meters (13 ft) above. Like other hadrosaurs, it could have moved both bipedally and quadrupedally. Social behavior As noted, there is bonebed evidence that this genus lived in groups during at least part of the year. ==Paleoecology==

, P. maximus in the right distance The Dinosaur Park Formation, home to Prosaurolophus maximus, is interpreted as a low-relief setting of rivers and floodplains that became more swampy and influenced by marine conditions over time as the Western Interior Seaway transgressed westward. The climate was warmer than present-day Alberta, without frost, but with wetter and drier seasons. Conifers were apparently the dominant canopy plants, with an understory of ferns, tree ferns, and flowering plants. In this well-studied formation, P. maximus is only known from the upper part, which had more of a marine influence than the lower section. It was the most common hadrosaurine of this section, which was deposited about 75.5 million years ago. 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. The roughly contemporaneous Two Medicine Formation, home to P. maximus, ==See also==