Prosaurolophus

*Prosaurolophus maximus*

* Timothy Bradley Artwork
* Robert F Walters Artwork

**Prosaurolophus** (/ˌproʊsɔːˈrɒləfəs/; meaning "before Saurolophus", in comparison to the later dinosaur with a similar head crest) is a genus of hadrosaurid (or duck-billed) dinosaur from the Late Cretaceous of North America. It is known from the remains of at least 25 individuals belonging to two species, including skulls and skeletons, but it remains obscure. Around 9 meters (30 feet), its fossils have been found in the late Campanian-age Upper Cretaceous Dinosaur Park Formation in Alberta, and the roughly contemporaneous Two Medicine Formation in Montana, dating to around 75.5-74.0 million years ago. Its most recognizable feature is a small solid crest formed by the nasal bones, sticking up in front of the eyes.

The type species is P. maximus, described by American paleontologist Barnum Brown of the American Museum of Natural History in 1916. A second species, P. blackfeetensis, was described by Jack Horner of the Museum of the Rockies in 1992. The two species were differentiated mainly by crest size and skull proportions.

## Description

Prosaurolophus was a large-headed duckbill; the most complete described specimen has a skull around 0.9 metres (3.0 ft) long on a skeleton about 8.5 metres (28 ft) long. It had a small, stout, triangular crest in front of the eyes; the sides of this crest were concave, forming depressions. The upper arm was relatively short.

When originally described by Brown, Prosaurolophus maximus was known from a skull and jaw. Half of the skull was badly weathered at the time of examination, and the level of the parietal was distortedly crushed upwards to the side. The different bones of the skull could be easily defined, with the exception of the parietals and nasal bones. Brown found that the skull of the already described genus Saurolophus is very similar overall to, but also smaller than the skull of P. maximus. A unique feature of a shortened frontal in lambeosaurines is also found in Prosaurolophus, and the other horned hadrosaurines Brachylophosaurus, Maiasaura, and Saurolophus. Although they lack a shorter frontal, the genera Edmontosaurus and Shantungosaurus share with saurolophins an elongated dentary.

Patches of preserved skin are known from two juvenile specimens, TMP 1998.50.1 and TMP 2016.37.1; these pertain to the ventral extremity of the ninth through fourteenth dorsal ribs, the caudal margin of the scapular blade, and the pelvic region. Small basement scales (scales which makeup the majority of the skin surface), 3–7 millimetres (0.12–0.28 in) 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) around 5 millimetres (0.20 in) wide and 29 millimetres (1.1 in) long are found interspersed in the smaller scales in the patches from the ribs and scapula (they are absent from the pelvic patches). Similar scales are known from the tail of the related Saurolophus angustirostris (on which they have been speculated to indicate pattern), and it is considered likely adult Prosaurolophus would've retained the feature scales on their flanks like the juveniles.

## History of discovery

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,[5] 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.

The second species, *P. blackfeetensis*, is based on a specimen in the Museum of the Rockies (MOR 454), which was described by another notable paleontologist, Jack Horner. This specimen, and the remains of three or four other individuals, were found in Glacier County, Montana. In this case, the fossils were found in a bonebed of *Prosaurolophus* remains, which indicates that the animals lived together for at least some time. The bonebed is interpreted as reflecting a group of animals that congregated near a water source during a drought.

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.

## 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, whereas others have not, instead finding it closer to Brachylophosaurus, Edmontosaurus, Gryposaurus, and Maiasaura.

## 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. Comparisons between the scleral rings of Prosaurolophus and modern birds and reptiles suggest that it may have been cathemeral, active throughout the day at short intervals.

### Social behavior

As noted, there is bonebed evidence that this genus lived in groups during at least part of the year. Additionally, it had several potential methods for display in a social setting. The bony facial crest is an obvious candidate, and nasal diverticula may also have been present. These 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 both visual and auditory signals.

## Paleoecology

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, is well known for its fossils of dinosaur nests, eggs, and young, produced by the hadrosaurids Hypacrosaurus stebingeri and Maiasaura, and the troodontid Troodon. The tyrannosaurid Daspletosaurus, caenagnathid Chirostenotes, dromaeosaurids Bambiraptor and Saurornitholestes, armored dinosaurs Edmontonia and Euoplocephalus, hypsilophodont Orodromeus, and horned dinosaurs Achelousaurus, Brachyceratops, Einiosaurus, and Styracosaurus ovatus were also present. This formation was more distant from the Western Interior Seaway, and higher and drier than the Dinosaur Park Formation. The age of Prosaurolophus maximus remains from this formation is from approximately 75.5 to 74.0 million years ago.

## JPInstitute.com Description

Prosaurolophus was an early member of the duck-billed dinosaur family. It was very similar to Saurolophus and probably represents an evolutionary step in that dinosaur's history. Like the other duck-billed dinosaurs, it had hind legs much longer than its front legs, which means it could walk and stand on two legs. It also had hundreds of teeth packed closely together to form what is called a dental battery that was used to grind tough plant fiber into mushy pulp.

There is some fossil evidence to suggest that Prosaurolophus could have grown to a size of almost 50 feet long. Its crest was shorter than that of Saurolophus, and it had a smaller bill.

## Dinosaur Field Guide Description

Prosaurolophus ("before Saurolophus"') is a duckbill dinosaur, one of the two-legged herbivorous dinosaurs known as ornithopods. It is a relatively unknown dinosaur, in need of a publicist. The first specimen was collected by the greatest dinosaur field paleontologist of the twentieth century, Barnum Brown of the American Museum of Natural History in New York. During World War I, Brown led an expedition along the Red Deer River in Alberta, Canada, where he collected some of the most perfect duckbill skeletons ever found--including this one. Prosaurolophus (and its probable descendant, Saurolophus) belongs to a subgroup of duckbills known as the Saurolophini, the rarest of all duckbills. These dinosaurs are sometimes hard to place in the "big picture" of duckbill evolution because they have features from both the hadrosaurines, or non-crested duckbills, and the lambeosaurines, or crested duckbills.

### Fun Facts

There are two species of Prosaurolophus. One was named by Jack Horner, the duckbill expert who inspired the character of Alan Grant in the Jurassic Park movies.

### Trivia

There are fewer duckbill experts than there are specimens of Prosaurolophus!

## Links

http://web.archive.org/web/20040214165130fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_prosa.html