Old Earth Ministries Online Dinosaur Curriculum
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Lesson 61 - Prosaurolophus
Prosaurolophus (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 long (29.5 ft), 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 76-75 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
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 are differentiated mainly by crest size and skull proportions.
Length: 29 feet
Date Range: 76 - 75 Ma, Campanian Age, Late Cretaceous Period
|Prosaurolophus maximus, collected 1921, Royal Ontario Museum, Toronto (Picture Source)|
Prosaurolophus was a large-headed duckbill; the most complete described specimen has a
Otherwise, its anatomy was unremarkable for a hadrosaurine hadrosaurid. Like nearly all hadrosaurids, the whole front of the skull was flat and broadened out to form a beak, ideal for clipping leaves and twigs from the forests of North America. The back of the mouth contained thousands of teeth suitable for grinding food before it was swallowed.
The two species are differentiated by details of the crest, and in profile, P. blackfeetensis is restored with a steeper, taller face than P. maximus. In P. blackfeetensis, at least, the crest migrated backward toward the eyes during growth.
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. It was a hadrosaurine hadrosaur, meaning it lacked a hollow crest.
The cladogram to the right is based on the 2004 review by Jack Horner, David B. Weishampel, and Catherine Forster, in the second edition of The Dinosauria. In this review, Prosaurolophus is closest to Gryposaurus. This is only one of many proposed cladograms for hadrosaurids.
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. 20 to 25 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. Although many species of hadrosaurs have been consolidated, this species was considered to be valid in the most recent review.
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 from about 76 to about 74 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. blackfeetensis, 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.
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.
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.
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