Saurolophus

Taxobox

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image_width = 250px
image_caption = A photograph of the panel mount of the holotype of "Saurolophus", from Barnum Brown, 1913
name = "Saurolophus"
fossil_range = Late Cretaceous
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Ornithischia
familia = Hadrosauridae
subfamilia = Hadrosaurinae
genus = "Saurolophus"
genus_authority = Brown, 1912
subdivision_ranks = Species
subdivision =
* "S. osborni" Brown, 1912 (type)
* "S. angustirostris" Rozhdestvensky, 1952
* ?"S. kryschtofovici" Riabinin, 1930 (dubious)

"Saurolophus" (pronEng|sɔˈrɒləfəs, meaning "reptile crest") is a genus of large hadrosaurine duckbill that lived about 70 million years ago, in the Late Cretaceous of North America (Canada) and Asia (Mongolia); it is one of the few genera of dinosaurs known from multiple continents. It is distinguished by a spike-like crest which projects up and back from the skull. "Saurolophus" was a herbivorous dinosaur which could move about either bipedally or quadrupedally.

The type species, "S. osborni", was described by Barnum Brown in 1912. The other valid species, "S. angustirostris", lived in Asia, and was described by Anatoly Konstantinovich Rozhdestvensky. A third species is considered dubious.

Description

"Saurolophus" is known from material including nearly complete skeletons, giving us a clear picture of its bony anatomy. "S. osborni", the rarer Albertan species, was around 9.8 meters long (32 feet), with its skull a meter long (3.3 feet).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 weight is estimated at 1.9 tonnes (2.1 tons).cite book|chapter=Saurolophus |last=Glut |first=Donald F. |authorlink=Donald F. Glut |title=Dinosaurs: The Encyclopedia |year=1997 |publisher=McFarland & Co |location=Jefferson, North Carolina |pages=788-789 |isbn=0-89950-917-7] "S. angustirostris", the Mongolian species, was larger; the type skeleton is roughly 12 meters long (39.4 ft), and larger remains are reported. Aside from size, the two species are virtually identical, with differentiation hindered by lack of study.cite book |last=Norman |first=David B. |authorlink=David B. Norman |coauthors=Sues, Hans-Dieter |editor=Benton, Michael J.; Shishkin, Mikhail A.; Unwin, David M.; and Kurochkin, Evgenii N. |title=The Age of Dinosaurs in Russia and Mongolia |year=2000 |publisher=Cambridge University Press |location=Cambridge |isbn=0-521-55476-X |pages=462-479 |chapter=Ornithopods from Kazakhstan, Mongolia and Siberia ]

Its most distinctive feature is its cranial crest, which is present in young individuals but is smaller. It is long and spike-like and projects upward and backward at about a 45 degree angle, starting from over the eyes. This crest is often described as solid, but appears to be solid only at the point, with internal chambers that may have had a respiratory and/or heat-regulation function.cite journal |last=Maryańska |first=Teresa |coauthors=and Osmólska, Halszka|year=1981 |title=Cranial anatomy of "Saurolophus angustirostris" with comments on the Asian Hadrosauridae (Dinosauria) |journal=Palaeontologia Polonica |volume=42 |pages=5–24 ]

Classification

Barnum Brown, who described the first specimens, put it in its own subfamily in "Trachodontidae" (=Hadrosauridae), the Saurolophinae. At the time, this also included "Corythosaurus" and "Hypacrosaurus", the only well-known examples of what would become Lambeosaurinae.cite journal |last=Brown |first=Barnum |authorlink=Barnum Brown |year=1914 |title="Corythosaurus casuarius", a new crested dinosaur from the Belly River Cretaceous, with provisional classification of the family Trachodontidae |journal=Bulletin of the American Museum of Natural History |volume=33 |issue=55 |pages=559–564 |url=http://digitallibrary.amnh.org/dspace/handle/2246/1734 |accessdate=2007-04-29 ] Brown thought that "Saurolophus" had an expanded tip to the ischium bone in the hip, as dinosaurs now recognized as lambeosaurines had, but this appears to have been based on a mistakenly associated lambeosaurine ischium. Additionally, he misinterpreted the crests of "Saurolophus" and lambeosaurines as being made of the same bones.cite journal |last=Sternberg |first=Charles M. |authorlink=Charles Mortram Sternberg |title=Classification of American duckbilled dinosaurs |journal=Journal of Paleontology |volume=28 |issue=3 |pages=382–383 ] The subfamily Saurolophinae is no longer accepted,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 ] although a clade within Hadrosaurinae including "Saurolophus" and a few other genera (including "Kritosaurus" and "Prosaurolophus") is sometimes found; this clade is informally known as Saurolophini. "Saurolophus" is accepted as a good hadrosaurine, as it has a hadrosaurine pelvis and a (largely) solid crest.

Discovery and history

Barnum Brown recovered the first described remains of "Saurolophus" in 1911, including a nearly complete skeleton (AMNH 5220). Now on display in the American Museum of Natural History, this skeleton was the first nearly complete dinosaur skeleton from Canada. It was found in rocks of early Maastrichtian age, in the Upper Cretaceous Horseshoe Canyon Formation (then known as the Edmonton Formation) near Tolman Ferry on the Red Deer River in Alberta. Brown wasted little time in describing his material,cite journal |last=Brown |first=Barnum |authorlink=Barnum Brown |year=1912 |title=A crested dinosaur from the Edmonton Cretaceous |journal=Bulletin of the American Museum of Natural History |volume=31 |issue=14 |pages=131–136 |url=http://digitallibrary.amnh.org/dspace/handle/2246/1401 |accessdate=2007-04-29 ] cite journal |last=Brown |first=Barnum |authorlink=Barnum Brown |year=1913 |title=The skeleton of "Saurolophus", a crested duck-billed dinosaur from the Edmonton Cretaceous |journal=Bulletin of the American Museum of Natural History |volume=32 |issue=19 |pages=387–393 |url=http://digitallibrary.amnh.org/dspace/handle/2246/1415 |accessdate=2007-04-29 ] giving it its own subfamily. "Saurolophus" was an important early reference for other hadrosaurs, as seen in the names of "Prosaurolophus" ("before "Saurolophus") and "Parasaurolophus" ("near "Saurolophus"). However, little additional material has been recovered and described.

Instead, more abundant remains from Asia have provided more data. Initial remains were not promising: a partial fragmentary ischium from Heilongjiang, China that Riabinin named "S. kryschtofovici".cite journal |last=Riabinin |first=Anatoly Nikolaenvich, N. |year=1930 |title=On the age and fauna of the dinosaur beds on the Amur River |journal=Mémoir, Société Mineral Russia |volume=59 |pages=41–51 |language=Russian ] Much better remains were soon recovered, though, but from Mongolia's early Maastrichtian-age Nemegt Formation. The 1947-49 Polish-Mongolian Paleontological Expedition recovered the large skeleton that became "S. angustirostris" as described by A.K. Rozhdestvensky.cite journal |last=Rozhdestvensky |first=A.K. |authorlink=Anatoly Konstantinovich Rozhdestvensky |year=1952 |title=A new representative of the duck-billed dinosaurs from the Upper Cretaceous deposits of Mongolia |journal=Dokladi Akademii Nauk S.S.S.R. |volume=86 |language=Russian |pages=405–408 ] Other skeletons from a variety of growth stages have also been discovered, and "S. angustirostris" is now the most abundant Asian hadrosaurid.

pecies

Two species are regarded as valid today: the type species "S. osborni", and "S. angustirostris". "S. osborni" (Brown, 1912) is known from a skull and skeleton, two other complete skulls, and skull fragments. "S. angustirostris" (Rozhdestvensky, 1952) is known from at least fifteen specimens. "S, kryschtofovici" (Riabinin, 1930) is not considered valid; either it is regarded as a dubious name, or as a synonym of "S. angustirostris" (although it predates "S. angustirostris").

Paleoecology

"S. osborni" shared the Horseshoe Canyon Formation with fellow hadrosaurids "Edmontosaurus" and hollow-crested "Hypacrosaurus", hypsilophodont "Parksosaurus", ankylosaurid "Euoplocephalus", nodosaurid "Edmontonia", horned dinosaurs "Montanoceratops", "Anchiceratops", "Arrhinoceratops", and "Pachyrhinosaurus", pachycephalosaurid "Stegoceras", ostrich-mimics "Ornithomimus" and "Struthiomimus", a variety of poorly-known small theropods including troodontids and dromaeosaurids, and the tyrannosaurs "Albertosaurus" and "Daspletosaurus".cite book |last=Weishampel |first=David B. |authorlink=David B. Weishampel |coauthors=Barrett, Paul M.; Coria, Rodolfo A.; Le Loueff, Jean; Xu Xing; Zhao Xijin; Sahni, Ashok; Gomani, Elizabeth M.P.; and Noto, Christopher N. |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=517-606 |chapter=Dinosaur distribution ] The dinosaurs from this formation are sometimes known as Edmontonian, after a land mammal age, and are distinct from those in the formations above and below.cite book|last=Dodson |first=Peter |authorlink=Peter Dodson |title=The Horned Dinosaurs: A Natural History|publisher = Princeton University Press |year=1996 |location=Princeton |pages=14-15 |isbn=0-691-05900-4] The Horseshoe Canyon Formation is interpreted as having a significant marine influence, due to an encroaching Western Interior Seaway, the shallow sea that covered the midsection of North America through much of the Cretaceous. "S. osborni" may have preferred to stay more landward.

"S. angustirostris" was one of the largest herbivores of the Nemegt Formation, which lacked large horned dinosaurs but had sauropods and a more diverse theropod fauna. It coexisted with the rare crested hadrosaurid "Barsboldia", flat-headed pachycephalosaurian "Homalocephale" and domed "Prenocephale", the large ankylosaurid "Tarchia", rare saltasaurid sauropods "Nemegtosaurus" and "Opisthocoelicaudia", the alvarezsaurid "Mononykus", three types of troodontids including "Saurornithoides", several oviraptorosaurians including "Rinchenia" and "Nomingia", the ostrich-mimics "Gallimimus" and "Deinocheirus", therizinosaurid "Therizinosaurus", tyrannosaurid relative "Bagaraatan", and the tyrannosaurid "Tarbosaurus". Unlike other Mongolian formations like the well-known Djadochta Formation that includes "Velociraptor" and "Protoceratops", the Nemegt is interpreted as being well-watered, like the Dinosaur Park Formation in Alberta.

Paleobiology

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Crest

The distinctive spike-like crest of "Saurolophus" has been interpreted in multiple ways, and could have had multiple functions. Brown compared it to the crest of a chameleon, and suggested it could provide an area for muscle attachment and a connection point for a nonbody back frill like that seen in the basilisk lizard. Peter Dodson interpreted similar features in other duckbills as having use in sexual identification.cite journal |last=Dodson |first=Peter |authorlink=Peter Dodson |year=1975 |title=Taxonomic implications of relative growth in lambeosaurine dinosaurs |journal=Systematic Zoology |volume=24 |pages=37–54 |doi=10.2307/2412696 ] Maryańska and Osmólska, noting the hollow base, suggested that the crest increased the surface area of the respiratory cavity, and helped in thermoregulation. James Hopson supported a function as a visual signal, and further mentioned the possibility that there were inflatable skin flaps over the nostrils that could have acted as resonators and additional visual 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 ] This idea has been picked up by authors of popular dinosaur works, such as David B. Norman who discussed hadrosaurid display at length and included a life restoration of such an adaptation in action.cite book |last=Norman |first=David B. |authorlink=David B. Norman |title=The Illustrated Encyclopedia of Dinosaurs: An Original and Compelling Insight into Life in the Dinosaur Kingdom|chapter=Hadrosaurids II |year=1985 |publisher=Crescent Books |location=New York|pages=122-127 |isbn=0-517-468905 ]

References

External links

* [http://internt.nhm.ac.uk/jdsml/nature-online/dino-directory/detail.dsml?Genusqtype=starts+with&disp=gall&identifier=sauro&sort=Genus&dataHeaderText_EX=dinosaurs+beginning+with+%27S%27&Genus=S&beginIndex=4&listPageURL=nameAZ%2edsml%3fGenusqtype%3dstarts%2bwith%26disp%3dgall%26sort%3dGenus%26Genus%3dS "Saurolophus", from the Natural History Museum]