Prosaurolophus

Taxobox
name = "Prosaurolophus"

---

image_width = 200px
image_caption = "Prosaurolophus" skeleton, Royal Tyrrell Museum
fossil_range = Late Cretaceous
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Ornithischia
subordo = Ornithopoda
infraordo = Iguanodontia
superfamilia = Hadrosauroidea
familia = Hadrosauridae
subfamilia = Hadrosaurinae
genus = "Prosaurolophus"
genus_authority=Brown, 1916
subdivision_ranks = Species
subdivision =
* "P. maximus" Brown, 1916 (type)
* "P. blackfeetensis" Horner, 1992

"Prosaurolophus" (pronEng|ˌproʊsɔˈrɒləfəs, 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, which were deposited around 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 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 are 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 meters long (2.9 ft) on a ~8.5 meter long skeleton (~28 ft).cite book |last=Lull |first=Richard Swann |authorlink=Richard Swann Lull |coauthors= and Wright, Nelda E. |title=Hadrosaurian Dinosaurs of North America |year=1942 |publisher=Geological Society of America |series=Geological Society of America Special Paper 40 |pages=226 ] 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.cite book |last=Lull |first=Richard Swann |authorlink=Richard Swann Lull |coauthors= and Wright, Nelda E. |title=Hadrosaurian Dinosaurs of North America |year=1942 |publisher=Geological Society of America |series=Geological Society of America Special Paper 40 |pages=172-175]

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.cite journal |last=Horner |first=John R. |authorlink=Jack Horner (paleontologist) |year=1992 |title=Cranial morphology of "Prosaurolophus" (Ornithischia: Hadrosauridae) with descriptions of two new hadrosaurid species and an evaluation of hadrosaurid phylogenetic relationships |journal=Museum of the Rockies Occasional Paper |volume=2 |pages=1–119 ]

Classification

clade|style=font-size:80%;line-height:100%
label1= Hadrosaurinae
1=clade
1="Lophorhothon"
label2=unnamed
2=clade
label1=unnamed
1=clade
1="Prosaurolophus"
label2=unnamed
2=clade
1="Gryposaurus"
label2=unnamed
2=clade
1="Edmontosaurus"
label2=unnamed
2=clade
1="Brachylophosaurus"
2="Maiasaura"
label2=unnamed
2=clade
1="Kritosaurus" "australis"
2="Naashoibitosaurus"
3="Saurolophus"

Because of its name, "Prosaurolophus" is often associated with "Saurolophus". However, this is contentious; some authors have found the animals to be closely related,cite book |last=Weishampel |first=David B. |authorlink=David B. Weishampel |coauthors=and Horner, Jack R. |editor= Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=1st |year=1990 |publisher=University of California Press |location=Berkeley |isbn=0-520-06727-4 |pages=534-561 |chapter=Hadrosauridae] cite journal |last=Gates |first=Terry A. |coauthors=Sampson, Scott D. |year=2007 |title=A new species of "Gryposaurus" (Dinosauria: Hadrosauridae) from the late Campanian Kaiparowits Formation, southern Utah, USA |journal=Zoological Journal of the Linnean Society |volume=151 |issue=2 |pages=351–376 |doi=10.1111/j.1096-3642.2007.00349.x ] whereas others have not, instead finding it closer to "Brachylophosaurus", "Edmontosaurus", "Gryposaurus", and "Maiasaura".cite book |last=Horner |first=John R. |authorlink=Jack Horner (paleontologist) |coauthors=Weishampel, David B.; and Forster, Catherine A |editor=Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=2nd |year= 2004|publisher=University of California Press |location=Berkeley |isbn=0-520-24209-2 |pages=438-463 |chapter=Hadrosauridae ] 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.

History

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.cite journal |last=Brown |first=Barnum |authorlink=Barnum Brown |year=1916 |title=A new crested trachodont dinosaur, "Prosaurolophus maximus" |journal=Bulletin of the American Museum of Natural History |volume=35 |issue=37 |pages=701–708 |url=http://digitallibrary.amnh.org/dspace/bitstream/2246/1328/1/B035a37.pdf |accessdate=2007-04-15] The skull had a damaged muzzle and was inadvertently reconstructed too long,cite book |last=Lull |first=Richard Swann |authorlink=Richard Swann Lull |coauthors= and Wright, Nelda E. |title=Hadrosaurian Dinosaurs of North America |year=1942 |publisher=Geological Society of America |series=Geological Society of America Special Paper 40 |pages=Plate 22 ] 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.cite journal |last=Parks |first=William A |authorlink=William Parks |title="Dyoplosaurus acutosquameus", a new genus and species of armoured dinosaur; and notes on a skeleton of "Prosaurolophus maximus" |year=1924 |journal=University of Toronto Studies, Geological Series |volume=18 |pages=1–35 ] 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.cite journal |last=Rogers |first=Raymond R. |year=1990 |title=Taphonomy of three dinosaur bone beds in the Upper Cretaceous Two Medicine Formation of northwestern Montana: Evidence for drought-related mortality |journal=Palaios |volume=5 |issue=5 |pages=394–413 |doi=10.2307/3514834] Although many species of hadrosaurs have been consolidated, this species was considered to be valid in the most recent review.

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.Eberth, David A. 2005. "The geology", in "Dinosaur Provincial Park", pp. 54–82.] 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.Braman, Dennis R., and Koppelhus, Eva B. 2005. "Campanian palynomorphs", in "Dinosaur Provincial Park", pp. 101–130.] 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.cite book |last=Ryan |first=Michael J. |coauthors=and Evans, David C. |editors=Currie, Phillip J., and Koppelhus, Eva |title=Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed |chapter=Ornithischian Dinosaurs |year=2005 |publisher=Indiana University Press |location=Bloomington |pages=312-348 |isbn=0-253-34595-2 ] 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".Weishampel, David B.; Barrett, Paul M.; Coria, Rodolfo A.; Le Loeuff, Jean; Xu Xing; Zhao Xijin; Sahni, Ashok; Gomani, Elizabeth, M.P.; and Noto, Christopher R. (2004). "Dinosaur Distribution", in "The Dinosauria" (2nd), pp. 517–606.]

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.

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.

ocial 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.cite journal |last=Hopson |first=James A. |year=1975 |title=The evolution of cranial display structures in hadrosaurian dinosaurs |journal=Paleobiology |volume=1 |issue=1 |pages=21–43 ]

References

External links

* [http://www.users.qwest.net/~jstweet1/hadrosaurinae.htm "Prosaurolophus"] at "Thescelosaurus"! (under Hadrosaurinae)
* [http://internt.nhm.ac.uk/jdsml/nature-online/dino-directory/detail.dsml?Genus=Prosaurolophus "Prosaurolophus"] , Natural History Museum
* [http://www.palaeos.com/Vertebrates/Units/320Ornithischia/320.750.html#Hadrosaurinae Hadrosaurinae] from Palaeos.com (technical)