Parasaurolophus
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2008-07-12T10:41:17Z
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{{Taxobox
| name = ''Parasaurolophus''
| image = Parasaurolophus cyrtocristatus.jpg
| image_width = 230px
| image_caption = ''Parasaurolophus cyrtocristatus'', [[Field Museum]].
| fossil_range = [[Late Cretaceous]]
| regnum = [[Animal]]ia
| phylum = [[Chordate|Chordata]]
| classis = [[Reptile|Sauropsida]]
| superordo = [[Dinosaur]]ia
| ordo = [[Ornithischia]]
| familia = [[Hadrosauridae]]
| subfamilia = [[Hadrosauridae|Lambeosaurinae]]
| genus = '''''Parasaurolophus'''''
| genus_authority = [[William Parks|Parks]], 1922
| subdivision_ranks = [[Species]]
| subdivision =
* ''P. walkeri'' <small>([[Type (zoology)|type]])</small>
* ''P. tubicen'' <small>[[Carl Wiman|Wiman]], 1931</small>
* ''P. cyrtocristatus'' <small>[[John Ostrom|Ostrom]], 1961</small>
}}
'''''Parasaurolophus''''' ({{pronEng|ˌpærəsɔˈrɒləfəs}}, in common usage also {{IPA|/ˌpærəˌsɔrəˈloʊfəs/}}; meaning "near crested lizard" in reference to ''[[Saurolophus]]'') is a [[genus]] of [[ornithopod]] [[dinosaur]] from the [[Late Cretaceous]] [[Period (geology)|Period]] of what is now [[North America]], about 76-73 million years ago. It was a [[herbivore]] that walked both as a [[bipedalism|biped]] and a [[quadruped]]. Three [[species]] are recognized: ''P. walkeri'' (the [[type species]]), ''P. tubicen'', and the short-crested ''P. cyrtocristatus''. Remains are known from [[Alberta]] ([[Canada]]), and [[New Mexico]] and [[Utah]] ([[USA]]). It was first described in 1922 by [[William Parks]] from a skull and partial skeleton in Alberta.
''Parasaurolophus'' is a [[hadrosaurid]], part of a diverse [[family (biology)|family]] of Cretaceous dinosaurs known for their range of bizarre head adornments. This genus is known for its large, elaborate cranial crest, which at its largest forms a long curved tube projecting upwards and back from the skull. ''[[Charonosaurus]]'' from [[People's Republic of China|China]], which may have been its closest relative, had a similar skull and potentially a similar crest. The crest has been much discussed by scientists; the consensus is that major functions included visual recognition of both species and sex, acoustic resonance, and [[thermoregulation]]. It is one of the rarer duckbills, known from only a handful of good specimens.
==Description==
[[Image:Human-parasaurolophus size comparison.svg|thumb|left|230px|The size of ''Parasaurolophus walkeri'' compared to a human.]]
As is the case with most dinosaurs, the skeleton of ''Parasaurolophus'' is incompletely known. The length of the [[type specimen]] of ''P. walkeri'' is estimated at 9.5 [[metre|meters]] (31 [[foot (unit of length|ft]]). Its skull is about 1.6 meters (5.2 ft) long, including the crest, whereas the type skull of ''P. tubicen'' is over 2.0 meters (6.6 ft) long, indicating a larger animal.<ref name=LW42a>{{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=p. 229 }}</ref> Its weight is estimated at 2.5 [[tonnes]] (2.7 [[short ton|tons]]).<ref name=DFG97>{{cite book|chapter=Parasaurolophus |last=Glut |first=Donald F. |authorlink=Donald F. Glut |title=Dinosaurs: The Encyclopedia |year=1997 |publisher=McFarland & Co |location=Jefferson, North Carolina |pages=pp. 678-684 |isbn=0-89950-917-7}}</ref> Its single known forelimb was relatively short for a hadrosaurid, with a short but wide [[scapula|shoulder blade]]. The [[femur|thighbone]] measures 103 [[centimetre|centimeters]] (3.38 ft) long in ''P. walkeri'' and is robust for its length when compared to other hadrosaurids.<ref name=LW42b>Lull and Wright, ''Hadrosaurian Dinosaurs of North America'', pp. 209-213.</ref> The [[humerus|upper arm]] and [[pelvis|pelvic]] bones were also heavily built.<ref name=BC06>{{cite book |last=Brett-Surman |first=Michael K. |coauthors=and Wagner, Jonathan R. |year=2006 |chapter=Appendicular anatomy in Campanian and Maastrichtian North American hadrosaurids |editor=Carpenter, Kenneth (ed.) |title=Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs |publisher=Indiana University Press |location=Bloomington and Indianapolis |pages=135-169 |isbn=0-253-34817-X}}</ref>
Like other hadrosaurids, it was able to walk on either two legs or four. It probably preferred to forage for food on four legs, but ran on two.<ref name=HWF04>{{cite book |last=Horner |first=John R. |authorlink=Jack Horner (paleontologist) |coauthors=Weishampel, David B.; and Forster, Catherine A |editor=Weishampel, David B.; Osmólska, Halszka; and Dodson, Peter (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 }}</ref> The [[spinous process|neural spines]] of the [[vertebra]]e were tall, as was common in lambeosaurines;<ref name=LW42b/> tallest over the hips, they increased the height of the back. [[Integumentary system|Skin]] impressions are known for ''P. walkeri'', showing uniform tubercle-like scales but no larger structures.<ref name=WAP22>{{cite journal |last=Parks |first=William A. |authorlink=William Parks |year=1922 |title=''Parasaurolophus walkeri'', a new genus and species of crested trachodont dinosaur |journal=University of Toronto Studies, Geology Series |volume=13 |pages=1–32}}</ref>
[[Image:Parasaurolophuspic steveoc.jpg|thumb|''Parasaurolophus walkeri'' with scalation detail.]]
The most noticeable feature was the cranial crest, which protruded from the rear of the head and was made up of the [[premaxilla]] and [[nasal bone]]s. The ''P. walkeri'' type specimen has a notch in the neural spines near where the crest would hit the back, but this may be a [[pathology]] peculiar to this individual.<ref name=LW42b/> William Parks, who named the genus, hypothesized that a [[ligament]] ran from the crest to the notch to support the head.<ref name=WAP22/> Although this idea seems unlikely,<ref name=DFG97/> ''Parasaurolophus'' is sometimes restored with a skin flap from the crest to the neck.
The crest was hollow, with distinct tubes leading from each nostril to the end of the crest before reversing direction and heading back down the crest and into the skull. The tubes were simplest in ''P. walkeri'', and more complex in ''P. tubicen'', where some tubes were blind and others met and separated.<ref name=SW99>{{cite book |last=Sullivan |first=Robert M. |coauthors=and Williamson, Thomas E. |year=1999 |title=A new skull of ''Parasaurolophus'' (Dinosauria: Hadrosauridae) from the Kirtland Formation of New Mexico and a revision of the genus |series=New Mexico Museum of Natural History and Science Bulletin, '''15''' |publisher=New Mexico Museum of Natural History and Science |location=Albuqueque, New Mexico |pages=pp. 1-52}}</ref> While ''P. walkeri'' and ''P. tubicen'' had long crests with only slight curvature, ''P. cyrtocristatus'' had a short crest with a more circular profile.<ref name=JHO61>{{cite journal |last=Ostrom |first=John H. |authorlink=John Ostrom |year=1961 |title=A new species of hadrosaurian dinosaur from the Cretaceous of New Mexico |journal=Journal of Paleontology |volume=35 |issue=3 |pages=575–577| url= |accessdate= }}</ref>
==Classification==
As its name implies, ''Parasaurolophus'' was initially thought to be closely related to ''[[Saurolophus]]'' because of its superficially similar crest.<ref name=WAP22/> However, it was soon reassessed as a member of the [[lambeosaurine]] subfamily of hadrosaurids—''Saurolophus'' is an [[hadrosaurine]].<ref name=CWG24>{{cite journal |last=Gilmore |first=Charles W. |authorlink=Charles Whitney Gilmore |year=1924 |title=On the genus ''Stephanosaurus'', with a description of the type specimen of ''Lambeosaurus lambei'', Parks |journal=Canada Department of Mines Geological Survey Bulletin (Geological Series) |volume=38 |issue=43 |pages=29–48}}</ref> It is usually interpreted as a separate offshoot of the lambeosaurines, distinct from the helmet-crested ''[[Corythosaurus]]'', ''[[Hypacrosaurus]]'', and ''[[Lambeosaurus]]''.<ref name=HWF04/><ref name=WH90>{{cite book |last=Weishampel |first=David B. |authorlink=David B. Weishampel |coauthors=and Horner, Jack R. |editor= Weishampel, David B.; Osmólska, Halszka; and Dodson, Peter (eds.)|title=The Dinosauria |edition=1st |year=1990 |publisher=University of California Press |location=Berkeley |isbn=0-520-06727-4 |pages=pp. 534-561 |chapter=Hadrosauridae}}</ref><ref name=ER07>{{cite journal |last=Evans |first=David C. |coauthors=and Reisz, Robert R. |year=2007|title= Anatomy and relationships of ''Lambeosaurus magnicristatus'', a crested hadrosaurid dinosaur (Ornithischia) from the Dinosaur Park Formation, Alberta |journal= Journal of Vertebrate Paleontology |volume= 27 |issue= 2 |pages=373–393| url=http://www.vertpaleo.org/publications/jvp/27-373-393.cfm| accessdate=2007-07-28|doi= 10.1671/0272-4634(2007)27[373:AAROLM]2.0.CO;2}}</ref> Its closest known relative appears to be ''[[Charonosaurus]]'', a lambeosaurine with a similar skull (but no complete crest yet) from the [[Amur]] region of northeastern China,<ref name=Getal00>{{cite journal |last=Godefroit |first=Pascal |coauthors=Shuqin Zan; and Liyong Jin |year=2000 |title=''Charonosaurus jiayinensis'' n. g., n. sp., a lambeosaurine dinosaur from the Late Maastrichtian of northeastern China |journal=Compte Rendus de l'Academie des Sciences, Paris, Sciences de la Terre et des planètes |volume=330 |pages=875–882| doi=10.1016/S1251-8050(00)00214-7}}</ref> and the two may form a [[clade]] Parasaurolophini.<ref name=ER07/> ''P. cyrtocristatus'', with its short, rounder crest, may be the most [[basal (phylogenetics)|basal]] of the three known ''Parasaurolophus'' species,<ref name=ER07/> or it may represent [[juvenile (organism)|subadult]] or female specimens of ''P. tubicen''.<ref name=TEW00>{{cite book |last=Williamson |first=Thomas E. |year=2000 |chapter=Review of Hadrosauridae (Dinosauria, Ornithischia) from the San Juan Basin, New Mexico |editor=Lucas, S.G.; and Heckert, A.B. (eds.) |title=Dinosaurs of New Mexico |series=New Mexico Museum of Natural History and Science Bulletin, '''17''' |publisher=New Mexico Museum of Natural History and Science |location=Albuqueque, New Mexico |pages=pp. 191-213}}</ref>
== Discovery and naming ==
[[Image:Pl dinozaur kaczodzioby.jpg|thumb|Cast of the incomplete ''Parasaurolophus walkeri'' type specimen in [[Warszawa]].]]
Meaning "near crested lizard", ''Parasaurolophus''' name is derived from the [[Ancient Greek|Greek]] ''para''/παρα "beside" or "near", ''saurus''/σαυρος "lizard" and ''lophos''/λοφος "crest".<ref name="Liddell 1980">{{cite book | author = [[Henry George Liddell|Liddell, Henry George]] and [[Robert Scott (philologist)|Robert Scott]] | year = 1980 | title = [[A Greek-English Lexicon]] (Abridged Edition) | publisher = Oxford University Press | location = United Kingdom | id = ISBN 0-19-910207-4}}</ref> It is [[holotype|based on]] [[Royal Ontario Museum|ROM]] 768, a skull and partial skeleton missing most of the tail and the hind legs below the knees, which was found by a field party from the [[University of Toronto]] in 1920 near Sand Creek along the [[Red Deer River]] in Alberta, Canada.<ref name=WAP22/> These rocks are now known as the [[Campanian]]-age [[Upper Cretaceous]] [[Dinosaur Park Formation]]. William Parks named the specimen ''P. walkeri'' in honor of Sir [[Byron Edmund Walker]], Chairman of the Board of Trustees of the [[Royal Ontario Museum]].<ref name=WAP22/> ''Parasaurolophus'' remains are rare in Alberta,<ref name=RE05>{{cite book |last=Ryan |first=Michael J. |coauthors=and Evans, David C. |editors=Currie, Phillip J., and Koppelhus, Eva (eds.) |title=Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed |chapter=Ornithischian Dinosaurs |year=2005 |publisher=Indiana University Press |location=Bloomington |pages=pp. 312-348 |isbn=0-253-34595-2 }}</ref> with only one other partial skull from (probably) the Dinosaur Park Formation,<ref name=ERD07>{{cite journal |last=Evans |first=David C. |coauthors=Reisz, Robert R.; and Dupuis, Kevin |year=2007 |title=A juvenile ''Parasaurolophus'' braincase from Dinosaur Provincial Park, Alberta, with comments on crest ontogeny in the genus |journal=Journal of Vertebrate Paleontology |volume=27 |issue=3 |pages=642–650 |doi=10.1671/0272-4634(2007)27[642:AJPOHB]2.0.CO;2}}</ref> and three Dinosaur Park specimens lacking skulls, possibly belonging to the genus.<ref name=RE05>Currie, Phillip J; and Russell, Dale A. "Geographic and stratigraphic distribution of dinosaur remains" in ''Dinosaur Provincial Park'', p. 553.</ref>
In 1921, [[Charles Hazelius Sternberg|Charles H. Sternberg]] recovered a partial skull ([[Uppsala University|PMU]].R1250) from what is now known as the slightly younger [[Kirtland Formation]] in [[San Juan County, New Mexico|San Juan County]], New Mexico. This specimen was sent to [[Uppsala]], [[Sweden]], where [[Carl Wiman]] described it as a second species, ''P. tubicen'', in 1931.<ref name=CW31>{{cite journal |last=Wiman |first=Carl |authorlink=Carl Wiman |year=1931 |title=''Parasaurolophus tubicen'', n. sp. aus der Kreide in New Mexico |journal=Nova Acta Regia Societas Scientarum Upsaliensis, series 4 |volume=7 |issue=5 |language=German |pages=1–11}}</ref> The specific epithet is derived from the [[Latin]] ''tǔbǐcěn'' "trumpeter".<ref name ="Latindictionary79"/> A second, nearly complete ''P. tubicen'' skull ([[New Mexico Museum of Natural History and Science|NMMNH]] P-25100) was found in New Mexico in 1995. Using [[computed tomography]] of this skull, Robert Sullivan and Thomas Williamson gave the genus a [[monograph]]ic treatment in 1999, covering aspects of its anatomy and taxonomy, and the functions of its crest.<ref name=SW99/> Williamson later published an independent review of the remains, disagreeing with the taxonomic conclusions.<ref name=TEW00/>
[[John Ostrom]] described another good specimen ([[Field Museum of Natural History|FMNH]] P27393) from New Mexico as ''P. cyrtocristatus'' in 1961. It includes a partial skull with a short, rounded crest, and much of the [[postcrania]]l skeleton except for the feet, neck, and parts of the tail.<ref name=JHO61/> Its specific name is derived from the [[Latin]] ''curtus'' "shortened" and ''cristatus'' "crested".<ref name ="Latindictionary79">{{cite book | last = Simpson | first = D.P. | title = Cassell's Latin Dictionary | publisher = Cassell Ltd. | date = 1979 | edition = 5 | location = London | pages =p. 883 | id = ISBN 0-304-52257-0}}</ref> The specimen was found in either the top of the [[Fruitland Formation]] or, more likely, the base of the overlying Kirtland Formation.<ref name=SW99/> The range of this species was expanded in 1979, when [[David B. Weishampel]] and [[James A. Jensen]] described a partial skull with a similar crest ([[Brigham Young University|BYU]] 2467) from the Campanian-age [[Kaiparowits Formation]] of [[Garfield County, Utah|Garfield County]], [[Utah]].<ref name=WJ79>{{cite journal |last=Weishampel |first=David B. |authorlink=David B. Weishampel |coauthors=and Jensen, James A. |year=1979 |title=''Parasaurolophus'' (Reptilia: Hadrosauridae) from Utah |journal=Journal of Paleontology |volume=53 |issue=6 |pages=1422–1427| url= |accessdate= }}</ref> Since then, another skull has been found in Utah with the short/round ''P. cyrtocristatus'' crest morphology.<ref name=SW99/>
=== Species ===
[[Image:Sketch parasaurolophus.jpg|thumb|''Parasaurolophus walkeri''.]]
The [[type species]] ''P. walkeri'', from Alberta, is known from a single specimen.<ref name=HWF04/> It differs from ''P. tubicen'' by having simpler tubes in its crest,<ref name=SW99/> and from ''P. cyrtocristatus'' by having a long, unrounded crest and a longer [[humerus|upper arm]] than [[radius (bone)|forearm]].<ref name=JHO61/>
''P. tubicen'', from New Mexico, is known from the remains of at least three individuals.<ref name=HWF04/> It is the largest species, with more complex air passages in its crest than ''P. walkeri'', and a longer, straighter crest than ''P. cyrtocristatus''.<ref name=SW99/>
''P. cyrtocristatus'', from New Mexico and Utah, is known from three possible specimens. It is the smallest species, with a short rounded crest.<ref name=SW99/> Its small size and the form of its crest have led several scientists to suggest that it represents juveniles or females of ''P. tubicen'', which is from roughly the same time and from the same formation in New Mexico. As noted by Thomas Williamson, the type material of ''P. cyrtocristatus'' is about 72% the size of ''P. tubicen'', close to the size at which other lambeosaurines are interpreted to begin showing definitive [[sexual dimorphism]] in their crests (~70% of adult size).<ref name=TEW00/> This position has been rejected in recent reviews of lambeosaurines.<ref name=HWF04/><ref name=ER07/>
==Paleoecology==
[[Image:GorgosaurusDB.jpg|thumb|left|''[[Gorgosaurus]]'' attacking a ''Parasaurolophus cyrtocristatus''.]]
''Parasaurolophus walkeri'', from the [[Dinosaur Park Formation]], was a member of a diverse and well-documented [[fauna]] of prehistoric animals, including well-known dinosaurs such as the [[ceratopsidae|horned]] ''[[Centrosaurus]]'', ''[[Styracosaurus]]'', and ''[[Chasmosaurus]]''; fellow duckbills ''[[Prosaurolophus]]'', ''[[Gryposaurus]]'', ''Corythosaurus'', and ''Lambeosaurus''; [[tyrannosaurid]] ''[[Gorgosaurus]]''; and [[ankylosauridae|armored]] ''[[Edmontonia]]'' and ''[[Euoplocephalus]]''.<ref name=WETAL04>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.</ref> It was a rare constituent of this fauna.<ref name=RE05/> The Dinosaur Park Formation is interpreted as a low-relief setting of [[river]]s and [[floodplain]]s that became more [[swamp]]y and influenced by [[ocean|marine]] conditions over time as the [[Western Interior Seaway]] [[transgression (geology)|transgressed]] westward.<ref name=DAE05>Eberth, David A. 2005. "The geology", in ''Dinosaur Provincial Park'', pp. 54-82.</ref> The [[climate]] was warmer than present-day Alberta, without [[frost]], but with wetter and drier seasons. [[Conifer]]s were apparently the dominant [[forest canopy|canopy]] plants, with an [[understory]] of [[fern]]s, [[tree fern]]s, and [[angiosperm]]s.<ref name=BK05>Braman, Dennis R., and Koppelhus, Eva B. 2005. "Campanian palynomorphs", in ''Dinosaur Provincial Park'', pp. 101-130.</ref>
The New Mexican species shared their environment with the large [[sauropod]] ''[[Alamosaurus]]'', duckbill ''[[Kritosaurus]]'', horned ''[[Pentaceratops]]'', armored ''[[Nodocephalosaurus]]'', ''[[Saurornitholestes]]'', and currently unnamed [[tyrannosaurid]]s.<ref name=WETAL04/> The Kirtland Formation is interpreted as river floodplains appearing after a retreat of the Western Interior Seaway. Conifers were the dominant plants, and [[Ceratopsidae|chasmosaurine]] horned dinosaurs were apparently more common than hadrosaurids.<ref name=DAR89>{{cite book |last=Russell |first=Dale A. |authorlink=Dale Russell |title=An Odyssey in Time: Dinosaurs of North America |year=1989 |publisher=NorthWord Press |location=Minocqua, Wisconsin |isbn=1-55971-038-1 |pages=pp. 160-164}}</ref>
==Paleobiology==
===Feeding===
As a hadrosaurid, ''Parasaurolophus'' was a large bipedal/quadrupedal herbivore, eating [[plant]]s with a sophisticated skull that permitted a grinding motion analogous to [[mastication|chewing]]. Its [[tooth|teeth]] were continually replacing and packed into dental batteries that contained hundreds of teeth, only a relative handful of which were in use at any time. It used its beak to crop plant material, which was held in the jaws by a [[cheek]]-like organ. Feeding would have been from the ground up to around 4 meters (13 ft) above.<ref name=HWF04/> As noted by [[Robert T. Bakker|Bob Bakker]], lambeosaurines have narrower beaks than hadrosaurines, implying that ''Parasaurolophus'' and its relatives could feed more selectively than their broad-beaked, crestless counterparts.<ref name=RTB86>{{cite book |last=Bakker |first=Robert T. |authorlink=Robert T. Bakker |year=1986 |title=[[The Dinosaur Heresies: New Theories Unlocking the Mystery of the Dinosaurs and their Extinction]] |publisher=William Morrow |location=New York |pages=p. 194 |isbn=0-8217-2859-8}}</ref>
=== Cranial crest ===
Many hypotheses have been advanced as to what functions the cranial crest of ''Parasaurolophus'' performed, but most have been discredited.<ref name=DBN85>{{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=pp. 122-127 |isbn=0-517-468905 }}</ref><ref name=DFG97/> It is now believed that it may have had several functions: visual display for identifying species and sex, sound amplification for communication, and thermoregulation. It is not clear which was most significant at what times in the evolution of the crest and its internal nasal passages.<ref name=DCE06/>
==== Differences between species and growth stages ====
[[Image:Parasaurolophus skull NHM.jpg|thumb|''Parasaurolophus walkeri'' skull - [[Natural History Museum]], [[London]].]]
[[Image:Parasaurolophus skull FMNH.jpg|thumb|''Parasaurolophus cyrtocristatus'' skull.]]
As for other lambeosaurines, it is believed that the cranial crest of ''Parasaurolophus'' changed with age and was a [[sexual dimorphism|sexually dimorphic]] characteristic in adults. [[James Hopson]], one of the first researchers to describe lambeosaurine crests in terms of such distinctions, suggested that ''P. cyrtocristatus'', with its small crest, was the female form of ''P. tubicen''.<ref name=JAH75>{{cite journal |last=Hopson |first=James A. |authorlink=James Hopson |year=1975 |title=The evolution of cranial display structures in hadrosaurian dinosaurs |journal=Paleobiology |volume=1 |issue=1 |pages=21–43 |url= |accessdate= }}</ref> Thomas Williamson suggested it was the [[juvenile (organism)|juvenile]] form.<ref name=TEW00/> Neither hypothesis became widely accepted. As only six good skulls and one juvenile braincase are known, additional material will help clear up these potential relationships. Williamson noted that in any case, juvenile ''Parasaurolophus'' probably had small, rounded crests like ''P. cyrtocristatus'', that probably grew faster as individuals approached [[sexual maturity]].<ref name=TEW00/> Recent restudy of a juvenile braincase previously assigned to ''Lambeosaurus'', now assigned to ''Parasaurolophus'', provides evidence that a small tubular crest was present in juveniles. This specimen preserves a small upward flaring of the [[frontal bone]]s that was similar to but smaller than what is seen in adult specimens; in adults, the frontals formed a platform that supported the base of the crest. This specimen also indicates that the growth of the crest in ''Parasaurolophus'' and the facial profile of juvenile individuals differed from the ''Corythosaurus''-''Hypacrosaurus''-''Lambeosaurus'' model, in part because the crest of ''Parasaurolophus'' lacks the thin bony 'coxcomb' that makes up the upper portion of the crest of the other three lambeosaurines.<ref name=ERD07/>
==== Rejected hypotheses about function ====
Many early suggestions focused on adaptations for an aquatic lifestyle, following the hypothesis that hadrosaurids were amphibious, a common line of thought until the 1960s. Thus, [[Alfred Sherwood Romer]] proposed it served as a [[Snorkel (swimming)|snorkel]],<ref name=ASR33>{{cite book |last=Romer |first=Alfred Sherwood |authorlink=Alfred Romer |year=1933 |title=Vertebrate Paleontology |publisher=University of Chicago Press |oclc=1186563 |pages=p. 491 }}</ref> Martin Wilfarth that it was an attachment for a mobile [[proboscis]] used as a breathing tube or for food gathering,<ref name=MW47>{{cite journal |last=Wilfarth |first=Martin |year=1947 |title=Russeltragende Dinosaurier |journal=Orion (Munich) |volume=2 |pages=pp. 525–532 |language=German }}</ref> [[Charles Mortram Sternberg|Charles M. Sternberg]] that it served as an airtrap to keep water out of the [[lung]]s,<ref name=CMS35>{{cite journal |last=Sternberg |first=Charles M. |authorlink=Charles Mortram Sternberg |year=1935 |title=Hooded hadrosaurs of the Belly River Series of the Upper Cretaceous |journal=Canada Department of Mines Bulletin (Geological Series) |volume=77 |issue=52 |pages=1–37 }}</ref> and [[Edwin Harris Colbert|Ned Colbert]] that it served as an air reservoir for prolonged stays underwater.<ref name=EHC45>{{cite book |last=Colbert |first=Edwin H. |authorlink=Edwin Harris Colbert |title=The Dinosaur Book: The Ruling Reptiles and their Relatives |year=1945 |publisher=American Museum of Natural History, Man and Nature Publications, '''14''' |location=New York |oclc=691246 |pages=156 }}</ref>
Other proposals were more physical in nature. As mentioned above, William Parks suggested that it was joined to the vertebrae with [[ligament]]s or muscles, and helped with moving and supporting the head.<ref name=WAP22/> [[Othenio Abel]] proposed it was used as a weapon in combat among members of the same species,<ref name=OA24>{{cite journal |last=Abel |first=Othenio |authorlink=Othenio Abel |yaer=1924 |title=Die neuen Dinosaurierfunde in der Oberkreide Canadas |journal=Jarbuch Naturwissenschaften |volume=12 |issue=36 |pages=709–716 |language=German |doi=10.1007/BF01504818 |year=1924}}</ref> and Angela Milner suggested that it could be used as a foliage deflector, like the helmet crest (called a 'casque') of the [[cassowary]].<ref name=DBN85/> Still other proposals made housing specialized organs the major function. [[Halszka Osmólska]] suggested that it housed [[salt gland]]s,<ref name=HO79>{{cite journal |last=Osmólska |first=Halszka |authorlink=Halszka Osmólska |year=1979 |title=Nasal salt glands in dinosaurs |journal=Acta Palaeontologica Polonica |volume=24 |pages=205–215 }}</ref> and John Ostrom suggested that it housed expanded areas for [[olfactory epithelium|olfactory tissue]] and much improved [[olfaction|sense of smell]] of the lambeosaurines, which had no obvious defensive capabilities.<ref name=JHO62>{{cite journal |last=Ostrom |first=John H. |authorlink=John Ostrom |year=1962 |title=The cranial crests of hadrosaurian dinosaurs |journal=Postilla |volume=62 |pages=1–29}}</ref> One unusual suggestion, made by [[creationist]] [[Duane Gish]], is that the crest housed chemical glands that allowed it to throw jets of chemical "fire" at enemies, similar to the modern-day [[bombardier beetle]].<ref name=DG92>{{cite book |last=Gish |first=Duane T. |year=1992 |title=Dinosaurs by Design |publisher=Master Books |location=Green Forest |pages=p. 82 |isbn=0-89051-165-9}}</ref>
Most of these hypotheses have been discredited or rejected.<ref name=DFG97/> For example, there is no hole at the end of the crest for a snorkeling function. There are no muscle scars for a proboscis and it is dubious that an animal with a beak would need one. As a proposed airlock, it would not have kept out water. The proposed air reservoir would have been insufficient for an animal the size of ''Parasaurolophus''. Other hadrosaurids had large heads without needing large hollow crests to serve as attachment points for supporting ligaments.<ref name=JHO62/> Also, none of the proposals explain why the crest has such a shape, why other lambeosaurines have crests that look much different but perform a similar function, how crestless or solid-crested hadrosaurids got along without such capabilities, or why some hadrosaurids had solid crests. These considerations particularly impact hypotheses based on increasing the capabilities of systems already present in the animal, such as the salt gland and olfaction hypotheses,<ref name=DBN85/> and indicate that these were not primary functions of the crest. Additionally, work on the nasal cavity of lambeosaurines shows that [[olfactory nerve]]s and corresponding sensory tissue were largely outside the portion of the nasal passages in the crest, so the expansion of the crest had little to do with the sense of smell.<ref name=DCE06>{{cite journal |last=Evans |first=David C. |year=2006 |title=Nasal cavity homologies and cranial crest function in lambeosaurine dinosaurs |journal=Paleobiology |volume=32 |issue=1 |pages=109–125 |url=http://findarticles.com/p/articles/mi_qa4067/is_200601/ai_n17169984| accessdate=2007-07-28}}</ref>
==== Social functions ====
Instead, social and [[physiology of dinosaurs|physiological]] functions have become more supported as function(s) of the crest, focusing on [[visual perception|visual]] and [[hearing (sense)|auditory]] identification and communication. As a large object, the crest has clear value as a visual signal, and sets this animal apart from its contemporaries. The large size of hadrosaurid [[orbit (anatomy)|eye sockets]] and the presence of [[sclerotic ring]]s in the eyes imply acute vision and [[diurnal]] habits, evidence that sight was important to these animals. If, as is commonly illustrated, a skin frill extended from the crest to the neck or back, the proposed visual display would have been even showier.<ref name=JAH75/> As is suggested by other lambeosaurine skulls, the crest of ''Parasaurolophus'' likely permitted both species identification (such as separating it from ''Corythosaurus'' or ''Lambeosaurus'') and sexual identification by shape and size.<ref name=DCE06/>
==== Sounding function ====
[[Image:Parasaurolophus crest interior.jpg|thumb|left|Computer model of the nasal passages in the crest of ''P. tubicen''.]]
However, the external appearance of the crest does not correspond to the complex internal anatomy of the nasal passages, which suggests another function accounted for usage of the internal space.<ref name=DCE06/> Carl Wiman was the first to propose, in 1931, that the passages served an auditory signaling function, like a [[crumhorn]];<ref name=CW31/> Hopson and David B. Weishampel revisited this idea in the 1970s and 1980s.<ref name=JAH75/><ref name=DBW81a>{{cite journal |last=Weishampel |first=David B. |authorlink=David B. Weishampel |year=1981 |title=Acoustic analyses of potential vocalization in lambeosaurine dinosaurs (Reptilia:Ornithischia) |journal=Paleobiology |volume=7 |issue=2 |pages=252–261 |url= |accessdate=}}</ref><ref name=DBW81b>{{cite journal |last=Weishampel |first=David B. |year=1981 |title=The nasal cavity of lambeosaurine hadrosaurids (Reptilia:Ornithischia): comparative anatomy and homologies |journal=Journal of Paleontology |volume=55 |issue=5 |pages=1046–1057| url= |accessdate= }}</ref> Hopson found that there is anatomical evidence that hadrosaurids had strong hearing. There is at least one example, in the related ''Corythosaurus'', of a slender [[stapes]] (reptilian ear bone) in place, which combined with a large space for an [[eardrum]] implies a sensitive [[middle ear]]. Furthermore, the hadrosaurid [[lagena]] is elongate like a [[crocodilia]]n's, indicating that the auditory portion of the [[inner ear]] was well-developed.<ref name=JAH75/> Weishampel suggested that ''P. walkeri'' was able to produce [[sound|frequencies]] of 48 to 240 [[hertz|Hz]], and ''P. cyrtocristatus'' (interpreted as a juvenile crest form) 75 to 375 Hz. Based on similarity of hadrosaurid [[inner ear]]s to those of [[crocodile]]s, he also proposed that adult hadrosaurids were sensitive to high frequencies, such as their offspring might produce. According to Weishampel, this is consistent with parents and offspring communicating.<ref name=DBW81a/>
Computer modeling of a well-preserved specimen of ''P. tubicen'', with more complex air passages than those of ''P. walkeri'', has allowed the reconstruction of the possible sound its crest produced.<ref name=Sandia>{{cite web |url=http://www.sandia.gov/media/dinosaur.htm |title= Scientists Use Digital Paleontology to Produce Voice of Parasaurolophus Dinosaur |accessdate=2007-06-30 |author=Sandia National Laboratories |date=1997-12-05}}</ref> The main path resonates at around 30 Hz, but the complicated sinus anatomy causes peaks and valleys in the sound.<ref name=DW98>{{cite journal |last=Diegert |first=Carl F. |coauthors=and Williamson, Thomas E. |year=1998 |title=A digital acoustic model of the lambeosaurine hadrosaur ''Parasaurolophus tubicen'' |journal=Journal of Vertebrate Paleontology |volume=18 |issue=3, Suppl. |pages=38A }}</ref>
==== Cooling function ====
The large surface area and [[vascularization]] of the crest also suggests a thermoregulatory function.<ref name=SW96>{{cite journal |last=Sullivan |first=Robert M. |coauthors=and Williamson, Thomas E. |year=1996 |title=A new skull of ''Parasaurolophus'' (long-crested form) from New Mexico: external and internal (CT scans) features and their functional implications |journal=Journal of Vertebrate Paleontology |volume=16 |issue=3, Suppl. |pages=68A }}</ref> P.E. Wheeler first suggested this use in 1978 as a way keep the [[brain]] cool.<ref name=PEW78>{{cite journal |last=Wheeler |first=P.E. |year=1978 |title=Elaborate CNS cooling structure in large dinosaurs |journal=Nature |volume=275 |pages=441–443 |doi=10.1038/275441a0}}</ref> [[Teresa Maryańska]] and Osmólska also proposed thermoregulation at about the same time,<ref name=MO79>{{cite journal |last=Maryańska |first=Teresa |authorlink=Teresa Maryańska |coauthors=and Osmólska, Halszka |year=1979 |title=Aspects of hadrosaurian cranial anatomy |journal=Lethaia |volume=12 |pages=265–273 |doi=10.1111/j.1502-3931.1979.tb01006.x }}</ref> and Sullivan and Williamson took further interest. David Evans' 2006 discussion of lambeosaurine crest functions was favorable to the idea, at least as an initial factor for the evolution of crest expansion.<ref name=DCE06/>
==References==
{{reflist|2}}
==External links==
{{Commons|Parasaurolophus}}
{{portalpar|Dinosaurs}}
*[http://www.sandia.gov/media/dinosaur.htm Scientists Use Digital Paleontology to Produce Voice of Parasaurolophus Dinosaur]; from Sandia National Laboratories.
*[http://skeletaldrawing.com/psgallery/images/parasaurolophuscomparison.jpg Restorations of ''P. walkeri'' and ''P. cyrtocristatus''], to the same scale, by Scott Hartman; at Skeletal Drawing.com.
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[[Category:Cretaceous dinosaurs]]
[[Category:Dinosaurs of North America]]
[[Category:Hadrosaurs]]
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