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{{Italic title}}{{Taxobox
{{Infobox Dinosaur
 
|name = Thescelosaurus
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| name = ''Thescelosaurus''
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| fossil_range = {{Geological range|78|66|Late Cretaceous}}
|image = [[File:Thescelosaurus BW3.jpg|190px]]
 
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| image = Thesc.png
|order = Ornithischia?
 
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| image_caption = ''Thescelosaurus'' restored with a smooth coat of protofeathers
|suborder = Hypsilophodontidae
 
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| image_width = 240px
|class = Thescelosauridae
 
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| regnum = [[Animal]]ia
|means = Vagarious saurian
 
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| phylum = [[Chordate|Chordata]]
|period = Late Cretaceous (67,5-65 million years ago)
 
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| classis = [[Sauropsida]]
|locate = New Mexico and United States of America
 
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| clade1 = [[Dinosauria]]
|diet = Herbivore?}}
 
 
| ordo = †[[Ornithischia]]
'''''Thescelosaurus''''' ({{IPAc-en|ˌ|θ|ɛ|s|ɨ|l|ə|ˈ|s|ɔr|ə|s}} {{respell|THESS|il-ə|SOR|əs}}; [[ancient Greek]] θέσκελος-/''theskelos-'' meaning "godlike", "marvelous", or "wondrous" and σαυρος/''sauros'' "lizard")<ref>{{cite book|author=Liddell & Scott|year=1980|title=Greek-English Lexicon, Abridged Edition |publisher=Oxford University Press, Oxford, UK|isbn=0-19-910207-4}}</ref> was a [[genus]] of small [[ornithopod]] [[dinosaur]] that appeared at the very end of the [[Late Cretaceous]] [[period (geology)|period]] in North America. It was a member of the last dinosaurian [[fauna]] before the [[Cretaceous–Paleogene extinction event]] around 66&nbsp;million years ago. The preservation and completeness of many of its specimens indicate that it may have preferred to live near streams.
 
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| subordo = †[[Ornithopoda]]
 
| familia = †[[Thescelosauridae]]
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| genus = †'''''Thescelosaurus'''''
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| genus_authority = [[Charles W. Gilmore|Gilmore]] et al., 1913
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| species = †'''''T. neglectus'''''
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| binomial = ''Thescelosaurus neglectus''
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| binomial_authority = Gilmore et al., 1913
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}}
 
'''''Thescelosaurus''''' (/ˌθɛsᵻləˈsɔːrəs/ thess-il-ə-sor-əs; ancient Greek θέσκελος-/theskelos- meaning "godlike", "marvelous", or "wondrous" and σαυρος/sauros "lizard")[2] was a genus of small ornithopod dinosaur that appeared at the very end of the Late Cretaceous period in North America. It was a member of the last dinosaurian fauna before the Cretaceous–Paleogene extinction event around 66 million years ago. The preservation and completeness of many of its specimens indicate that it may have preferred to live near streams.
   
This [[bipedalism|bipedal]] ornithopod is known from several partial skeletons and skulls that indicate it grew to between 2.5 and 4.0&nbsp;meters (8.2 to 13.1&nbsp;ft) in length on average. It had sturdy hind limbs, small wide hands, and a head with an elongate pointed snout. The [[morphology (biology)|form]] of the teeth and jaws suggest a primarily herbivorous animal. This genus of dinosaur is regarded as a specialized [[basal (phylogenetics)|basal]] ornithopod, traditionally described as a [[hypsilophodont]], but more recently recognized as distinct from ''[[Hypsilophodon]]''. Several species have been suggested for this genus. Three currently are recognized as [[valid name (zoology)|valid]]: the [[type species]] ''T. neglectus'', ''T. garbanii'' and ''T. assiniboiensis''.
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This bipedal ornithopod is known from several partial skeletons and skulls that indicate it grew to between 2.5 and 4.0 meters (8.2 to 13.1 ft) in length on average. It had sturdy hind limbs, small wide hands, and a head with an elongate pointed snout. The form of the teeth and jaws suggest a primarily herbivorous animal. This genus of dinosaur is regarded as a specialized basal ornithopod, traditionally described as a hypsilophodont, but more recently recognized as distinct from Hypsilophodon. Several species have been suggested for this genus. Three currently are recognized as valid: the type species T. neglectus, T. garbanii and T. assiniboiensis.
   
The genus attracted media attention in 2000, when a specimen unearthed in 1993 in [[South Dakota]], United States, was interpreted as including a [[fossil]]ized heart. There was much discussion over whether the remains were of a heart. Many scientists now doubt the identification of the object and the implications of such an identification.
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The genus attracted media attention in 2000, when a specimen unearthed in 1993 in South Dakota, United States, was interpreted as including a fossilized heart. There was much discussion over whether the remains were of a heart. Many scientists now doubt the identification of the object and the implications of such an identification.
   
 
==Description==
 
==Description==
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Thescelosaurus was a heavily built bipedal animal, probably herbivorous, but potentially not.[3] There was a prominent ridge along the length of both maxillae (the tooth-bearing "cheek" bones),[1] and a ridge on both dentaries (tooth-bearing bone of the lower jaw).[4] The ridges[4] and position of the teeth, deeply internal to the outside surface of the skull, are interpreted as evidence for muscular cheeks.[5] Aside from the long narrow beak, the skull also had teeth in the premaxilla, or upper beak (a primitive trait among ornithopods).[6] Long rod-like bones called palpebrals were present over the eyes, giving the animal heavy bony eyebrows.[6] Its teeth were of two types: small pointed premaxillary teeth, and leaf-shaped cheek teeth.[7] Six small teeth were present in both premaxillae, with a toothless section at the tip of the beak.[1]
[[File:Thescelosaurus BW3.jpg|thumb|left|''Thescelosaurus neglectus'' restoration]]
 
''Thescelosaurus'' was a heavily built bipedal animal, probably herbivorous,<ref name=NSWC04>{{cite book |last=Norman |first=David B. |authorlink=David B. Norman |author2=Sues, Hans-Dieter |author3=Witmer, Larry M. |author4= Coria, Rodolfo 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=393–412 |chapter=Basal Ornithopoda}}</ref> but possibly [[omnivore|omnivorous]].<ref name=TT>{{cite web | author = Triebold Paleontology, Inc. | title = Thescelosaurus | url= http://www.trieboldpaleontology.com/specimens/dinosaurs/ornithischian/thescelosaurus-neglectus-jonathan-ornithischian/ | accessdate = 2013-02-13}}</ref> There was a prominent ridge along the length of both [[maxilla]]e (the tooth-bearing "cheek" bones),<ref name=CABetal09>{{cite journal|last=Boyd|first=Clint A.|author2=Brown, Caleb M. |author3=Scheetz, Rodney D. |author4= Clarke, Julia A. |year=2009|title=Taxonomic revision of the basal neornithischian taxa ''Thescelosaurus'' and ''Bugenasaura''|journal=Journal of Vertebrate Paleontology|volume=29|issue=3|pages=758–770|doi=10.1671/039.029.0328}}</ref> and a ridge on both [[dentary|dentaries]] (tooth-bearing bone of the lower jaw).<ref name=PMG99>{{cite journal |last=Galton |first=Peter M. |authorlink=Peter Galton |year=1999 |title=Cranial anatomy of the hypsilophodont dinosaur ''Bugenasaura infernalis'' (Ornithischia: Ornithopoda) from the Upper Cretaceous of North America |journal=Revue Paléobiologie, Genève |volume=18 |issue=2 |pages=517–534 }}</ref> The ridges<ref name=PMG99/> and position of the teeth, deeply internal to the outside surface of the skull, are interpreted as evidence for muscular cheeks.<ref name=WJM76>{{cite book |last=Morris |first=William J. |editor=Churcher, C.S. (ed.) |title=Athlon |year=1976 |publisher=Royal Ontario Museum |location=Toronto |isbn=0-88854-157-0 |pages=93–113 |chapter=Hypsilophodont dinosaurs: a new species and comments on their systematics}}</ref> Aside from the long narrow beak, the skull also had teeth in the [[premaxilla]], or upper beak (a primitive trait among ornithopods).<ref name=PMG97>{{cite journal |last=Galton |first=Peter M. |authorlink=Peter Galton |year=1997 |title=Cranial anatomy of the basal hypsilophodontid dinosaur ''Thescelosaurus neglectus'' Gilmore (Ornithischia; Ornithopoda) from the Upper Cretaceous of North America |journal=Revue Paléobiologie, Genève |volume=16 |issue=1 |pages=231–258 }}</ref> Long rod-like bones called [[palpebral (bone)|palpebrals]] were present over the eyes, giving the animal heavy bony eyebrows.<ref name=PMG97/> Its teeth were of [[heterodont|two types]]: small pointed premaxillary teeth, and leaf-shaped cheek teeth.<ref name=CMS40>{{cite journal |last=Sternberg |first=Charles M. |authorlink=Charles Mortram Sternberg |year=1940 |title=''Thescelosaurus edmontonensis'', n. sp., and classification of the Hypsilophodontidae |journal=Journal of Paleontology |volume=14 |issue=5 |pages=481–494 }}</ref> Six small teeth were present in both premaxillae, with a toothless section at the tip of the beak.<ref name=CABetal09/>
 
   
Thescelosaurs had short, broad, five-fingered hands, four-toed feet with [[hoof]]-like [[phalanx bones|toe tips]], and a long tail braced by [[ossification|ossified]] [[tendon]]s from the middle to the tip, which would have reduced the flexibility of the tail.<ref name=CWG15>{{cite journal |last=Gilmore |first=Charles W. |authorlink=Charles W. Gilmore |year=1915 |title=Osteology of ''Thescelosaurus'', an orthopodus dinosaur from the Lance Formation of Wyoming |journal=Proceedings of the U.S. National Museum |volume=49 |issue=2127 |pages=591–616 |url=http://si-pddr.si.edu/dspace/bitstream/10088/14925/1/USNMP-49_2127_1915.pdf |format=pdf |doi=10.5479/si.00963801.49-2127.591}}</ref> The rib cage was broad, giving it a wide back, and the limbs were robust.<ref name=CMS40/> The animals may have been able to move on [[quadruped|all fours]], given its fairly long arms and wide hands,<ref name=PMG74/> but this idea has not been widely discussed in the scientific literature, although it does appear in popular works.<ref name=DL90>{{cite book |last=Lambert |first=David |author2=the Diagram Group |title=The Dinosaur Data Book |year=1990 |publisher=Avon Books |location=New York |isbn=0-380-75896-2 |chapter=Thescelosaurids |page=153}}</ref><ref name=LG93>{{cite book|title=The Dinosaur Society Dinosaur Encyclopedia|year=1993 |last=Lessem |first=Donald |authorlink=Don Lessem |author2=Glut, Donald F. |publisher=Random House, Inc.|isbn=0-679-41770-2 |page=475}}</ref> [[Charles Mortram Sternberg|Charles M. Sternberg]] reconstructed it with the [[humerus|upper arm]] oriented almost perpendicular to the body,<ref name=CMS40/> another idea that has gone by the wayside. As noted by [[Peter Galton]], the upper arm bone of most ornithischians articulated with the shoulder by an articular surface that consisted of the entire end of the bone, instead of a distinct ball and socket as in mammals. The orientation of the shoulder's articular surface also indicates a vertical and not horizontal upper arm in dinosaurs.<ref name=PMG70>{{cite journal |last=Galton |first=Peter M. |authorlink=Peter Galton |year=1970 |title=The posture of hadrosaurian dinosaurs |journal=Journal of Paleontology |volume=44 |issue=3 |pages=464–473 }}</ref>
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Thescelosaurs had short, broad, five-fingered hands, four-toed feet with hoof-like toe tips, and a long tail braced by ossified tendons from the middle to the tip, which would have reduced the flexibility of the tail.[8] The rib cage was broad, giving it a wide back, and the limbs were robust.[7] The animals may have been able to move on all fours, given its fairly long arms and wide hands,[9] but this idea has not been widely discussed in the scientific literature, although it does appear in popular works.[10][11] Charles M. Sternberg reconstructed it with the upper arm oriented almost perpendicular to the body,[7] another idea that has gone by the wayside. As noted by Peter Galton, the upper arm bone of most ornithischians articulated with the shoulder by an articular surface that consisted of the entire end of the bone, instead of a distinct ball and socket as in mammals. The orientation of the shoulder's articular surface also indicates a vertical and not horizontal upper arm in dinosaurs.[12]
   
Large thin flat mineralized plates have been found next to the ribs' sides.<ref name=FRSBHK00>{{cite journal |last=Fisher |first=Paul E. |author2=Russell, Dale A. |author3=Stoskopf, Michael K. |author4=Barrick, Reese E. |author5=Hammer, Michael |author6= Kuzmitz, Aandrew A. |date=April 2000 |title=Cardiovascular evidence for an intermediate or higher metabolic rate in an ornithischian dinosaur |journal=Science |volume=288 |issue=5465 |pages=503–505 |doi=10.1126/science.288.5465.503 |url=http://www.sciencemag.org/cgi/reprint/288/5465/503.pdf?ijkey=c75f52279333bdb9fa3d0504b786c07f9e35e2f9 |accessdate=2007-03-10 |pmid=10775107 |bibcode=2000Sci...288..503F}}</ref> Their function is unknown; they may have played a role in [[respiration (physiology)|respiration]].<ref name=NCA04>{{cite journal |last=Novas |first=Fernando E. |author2=Cambiaso, Andrea V |author3= Ambrioso, Alfredo |year=2004 |title=A new basal iguanodontian (Dinosauria, Ornithischia) from the Upper Cretaceous of Patagonia |journal=Ameghiniana |volume=41 |issue=1 |pages=75–82 }}</ref> However, muscle scars or other indications of attachment have not been found for the plates, which argues against a respiratory function. Recent histological study of layered plates from a probable subadult indicates that they may have started as [[cartilage]] and became bone as the animal aged.<ref name=BC08>{{cite journal |last=Boyd |first=Clint A. |author2=Cleland, Timothy P. |year=2008 |title=The morphology and histology of thoracic plates on neornithischian dinosaurs |journal=Abstract with Programs - Geological Society of America; Southeast Section, 57th Annual Meeting |volume=40 |issue=2 |pages=2 |url=http://gsa.confex.com/gsa/2008SE/finalprogram/abstract_136807.htm}}</ref> Such plates are known from several other ornithopods and their [[cerapoda]]n relatives.<ref name=BG08>{{cite journal |last=Butler |first=Richard J. |author2=Galton, Peter M. |year=2008 |title=The 'dermal armour' of the ornithopod dinosaur ''Hypsilophodon'' from the Wealden (Early Cretaceous: Barremian) of the Isle of Wight: a reappraisal |journal=Cretaceous Research |volume=29 |issue=4 |pages=636–642 |doi=10.1016/j.cretres.2008.02.002}}</ref>
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Large thin flat mineralized plates have been found next to the ribs' sides.[13] Their function is unknown; they may have played a role in respiration.[14] However, muscle scars or other indications of attachment have not been found for the plates, which argues against a respiratory function. Recent histological study of layered plates from a probable subadult indicates that they may have started as cartilage and became bone as the animal aged.[15] Such plates are known from several other ornithopods and their cerapodan relatives.
[[File:Human-thescelosaurus size comparison.png|thumb|The size of ''Thescelosaurus'' compared to a human]]
 
The nature of this genus' [[integument]], be it scales or something else, is currently unknown, although potential evidence exists: [[Charles W. Gilmore|Charles Gilmore]] described patches of [[carbon]]ized material near the shoulders as possible [[epidermis (skin)|epidermis]], with a "punctured" texture, but no regular pattern,<ref name=CWG15/> and William J. Morris suggested that [[armour (zoology)|armor]] was present, in the form of small [[scute]]s he interpreted as located at least along the midline of the neck of one specimen.<ref name=WJM76/> Scutes have not been found with other articulated specimens of ''Thescelosaurus'', though, and Morris's scutes could be [[crocodilia]]n in origin.<ref name=BG08/>
 
   
 
The nature of this genus' integument, be it scales or something else, is currently unknown, although potential evidence exists: Charles Gilmore described patches of carbonized material near the shoulders as possible epidermis, with a "punctured" texture, but no regular pattern,[8] and William J. Morris suggested that armor was present, in the form of small scutes he interpreted as located at least along the midline of the neck of one specimen.[5] Scutes have not been found with other articulated specimens of Thescelosaurus, though, and Morris's scutes could be crocodilian in origin.[16]
Overall, the skeletal anatomy of this genus is well documented, and restorations have been published in several papers, including skeletal restorations<ref name=CABetal09/><ref name=PMG74/><ref name=CWG15/><ref name=MKBS97>{{cite book |last=Brett-Surman |first=Michael K. |editor=Farlow, James O.; and Brett-Surman, Michael K. (eds.) |title=The Complete Dinosaur |year=1997 |publisher=Indiana University Press |location=Bloomington and Indianapolis |isbn=0-253-33349-0 |pages=330–346 |chapter=Ornithopods }}</ref> and models.<ref name=CMS40/><ref name=CWG15/> The skeleton is known well enough that a detailed reconstruction of the hip and hindlimb muscles has been made.<ref name=ASR27>{{cite journal |doi=10.1111/j.1463-6395.1927.tb00653.x |last=Romer |first=Alfred S. |authorlink=Alfred Sherwood Romer |year=1927 |title=The pelvic musculature of ornithischian dinosaurs |journal=Acta Zoologica |volume=8 |pages=225–275 |issue=2–3 }}</ref> The animal's size has been estimated in the 2.5–4.0&nbsp;m range for length (8.2–13.1&nbsp;ft)<ref name=PMG74/> for various specimens, and a weight of 200–300&nbsp;[[kilogram]]s (450–660&nbsp;[[pound (mass)|pounds]]),<ref name=BRE03b>{{cite book |last=Erickson |first=Bruce R. |authorlink=Bruce Erickson (paleontologist)|title=Dinosaurs of the Science Museum of Minnesota |year=2003 |publisher=The Science Museum of Minnesota |location=St. Paul, Minnesota |page=31 }}</ref> with the large [[type specimen]] of ''T. garbanii'' estimated at 4–4.5 meters (13.1–14.8&nbsp;feet) long.<ref name=WJM76/> As discussed more fully under "[[#Discovery, history, and species|Discovery, history, and species]]", it may have been [[sexual dimorphism|sexually dimorphic]], with one [[sex]] larger than the other.<ref name=PMG74/> [[juvenile (organism)|Juvenile]] remains are known from several locations, mostly based on teeth.<ref name=KC82>{{cite journal |last=Carpenter |first=Kenneth |authorlink=Kenneth Carpenter |year=1982 |title=Baby dinosaurs from the Late Cretaceous Lance and Hell Creek formations and a description of a new species of theropod |journal=Contributions to Geology |volume=20 |issue=2 |pages=123–134 }}</ref><ref name=RM02>{{cite book |last=Russell |first=Dale A. |authorlink=Dale Russell |author2=Manabe, Makoto |chapter=Synopsis of the Hell Creek (uppermost Cretaceous) dinosaur assemblage |editor=Hartman, Joseph H.; Johnson, Kirk R.; and Nichols, Douglas J. (eds.) |title=The Hell Creek Formation and the Cretaceous-Tertiary Boundary in the Northern Great Plains: An Integrated Continental Record of the End of the Cretaceous |year=2002 |series=''Geological Society of America Special Paper'', 361 |publisher=Geological Society of America |location=Boulder, Colorado |pages=169–176 |isbn=0-8137-2361-2 }}</ref>
 
   
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Overall, the skeletal anatomy of this genus is well documented, and restorations have been published in several papers, including skeletal restorations[1][8][9][17] and models.[7][8] The skeleton is known well enough that a detailed reconstruction of the hip and hindlimb muscles has been made.[18] The animal's size has been estimated in the 2.5–4.0 m range for length (8.2–13.1 ft)[9] for various specimens, and a weight of 200–300 kilograms (450–660 pounds),[19] with the large type specimen of T. garbanii estimated at 4–4.5 meters (13.1–14.8 feet) long.[5] As discussed more fully under "Discovery, history, and species", it may have been sexually dimorphic, with one sex larger than the other.[9] Juvenile remains are known from several locations, mostly based on teeth.
==Classification==
 
[[File:Thescelosaurus skeleton.jpg|thumb|left|Head and arms of ''Thescelosaurus'', [[Rocky Mountain Dinosaur Resource Center]]]]
 
''Thescelosaurus'' has generally been allied to ''[[Hypsilophodon]]'' and other small ornithopods as a [[hypsilophodont]]id, although recognized as being distinct among them for its robust build, unusual hindlimbs, and, more recently, its unusually long skull.<ref name=NSWC04/><ref name=PMG74/><ref name=CMS40/><ref name=SN90>{{cite book |last=Sues |first=Hans-Dieter |author2=Norman, David B. |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=498–509 |chapter=Hypsilophodontidae, ''Tenontosaurus'', Dryosauridae}}</ref> [[Peter Galton]] in 1974 presented one twist to the classic arrangement, suggesting that because of its hindlimb structure and heavy build (not [[cursorial]], or built for running, by his definition), it should be included in the [[Iguanodont]]idae. This has not been followed, with Morris arguing strongly against Galton's classification scheme.<ref name=WJM76/> At any rate, Galton's Iguanodontidae was [[polyphyly|polyphyletic]] and not a natural group, and so would not be recognized under modern [[cladistic]] usage.
 
   
 
== In popular culture ==
Although Hypsilophodontidae was interpreted as a natural group in the early 1990s,<ref name=SN90/><ref name=WH92>{{cite journal |last=Weishampel |first=David B. |authorlink=David B. Weishampel |author2=Heinrich, Ronald E. |year=1992 |title=Systematics of Hypsilophodontidae and Basal Iguanodontia (Dinosauria: Ornithopoda) |journal=Historical Biology |volume=6 |pages=159–184 |url=http://www.tandf.co.uk/journals/pdf/ghbi_06_01_01.pdf |format=PDF |accessdate=2007-03-10 |doi=10.1080/10292389209380426 |issue=3 }}</ref> this hypothesis has fallen out of favor and Hypsilophodontidae has been found to be an unnatural family composed of a variety of animals more or less closely related to Iguanodontia ([[paraphyly]]), with various small [[clade]]s of closely related taxa.<ref name=CABetal09/><ref name=NSWC04/><ref name=Hanetal12>{{cite journal |last=Han |first=Feng-Lu |author2=Paul M. Barrett |author3=Richard J. Butler |author4=Xing Xu |year=2012 |title=Postcranial anatomy of ''Jeholosaurus shangyuanensis'' (Dinosauria, Ornithischia) from the Lower Cretaceous Yixian Formation of China |url=http://www.tandfonline.com/doi/full/10.1080/02724634.2012.694385
 
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*In the film ''[[We're Back! A Dinosaur's Story]]'', a Thescelosaurus that Rex (as a "real animal") chases.
|journal=Journal of Vertebrate Paleontology |volume=32 |issue=6 |pages=1370–1395 |doi=10.1080/02724634.2012.694385 }}</ref><ref name=WJCN03/><ref name=VMK07>{{cite journal |last=Varricchio |first=David J. |author2=Martin, Anthony J. |author3= Katsura, Yoshihiro |year=2007 |title=First trace and body fossil evidence of a burrowing, denning dinosaur |journal=Proceedings of the Royal Society B: Biological Sciences |pmid=17374596 |volume=274 |issue=1616 |pmc=2176205 |pages=1361–1368 |doi=10.1098/rspb.2006.0443 |url=http://journals.royalsociety.org/content/uj1k12wh01587821/fulltext.pdf |format=PDF|accessdate=2007-03-22 }}</ref> "Hypsilophodontidae" and "hypsilophodont" are better understood as informal terms for an [[evolutionary grade]], not a true clade. ''Thescelosaurus'' has been regarded as both very basal<ref name=WH92/> and very [[Synapomorphy|derived]]<ref name=NSWC04/> among the hypsilophodonts. One issue that has potentially interfered with classifying ''Thescelosaurus'' is that not all of the remains assigned to ''T. neglectus'' necessarily belong to it.<ref name=BUN08>{{cite journal |last=Butler |first=Richard J. |author2=Upchurch, Paul|author3=and [[David B. Norman|Norman, David B.]] |title=The phylogeny of the ornithischian dinosaurs|journal=Journal of Systematic Palaeontology |volume=6 |issue=1 |year=2008 |pages=1–40 |doi=10.1017/S1477201907002271}}</ref> Clint Boyd and colleagues found that while the clade ''Thescelosaurus'' included the genus ''Bugenasaura'' and the species that had been assigned to that genus, there were at least two and possibly three species within ''Thescelosaurus'', and several specimens previously assigned to ''T. neglectus'' could not yet be assigned to a species within the genus.<ref name=CABetal09/> It appears to be closely related to ''[[Parksosaurus]]''.<ref name=CABetal09/><ref name=NSWC04/><ref name=WJCN03>{{cite journal |last=Weishampel |first= David B. |authorlink=David B. Weishampel |author2=Jianu, Coralia-Maria |author3=Csiki, Z. |author4= Norman, David B. |year=2003 |title=Osteology and phylogeny of ''Zalmoxes'' (n.g.), an unusual euornithopod dinosaur from the latest Cretaceous of Romania |journal=Journal of Systematic Palaeontology |volume=1 |issue=2 |pages=1–56 |doi=10.1017/S1477201903001032 }}</ref><ref name=CMBetal2011>{{cite journal |authors=Brown; Caleb M.; Boyd, Clint A.; and Russell, Anthony P. |year=2011 |title=A new basal ornithopod dinosaur (Frenchman Formation, Saskatchewan, Canada), and implications for late Maastrichtian ornithischian diversity in North America |url=http://onlinelibrary.wiley.com/doi/10.1111/j.1096-3642.2011.00735.x/abstract |journal=Zoological Journal of the Linnean Society |volume=163 |issue=4 |pages=1157–1198 |doi=10.1111/j.1096-3642.2011.00735.x }}</ref><ref name=CMBetal13/>
 
[[File:Thescelosaurus skull.png|thumb|Skull of specimen NCSM 15728 in left and right view]]
 
The dissolution of Hypsilophodontidae has been followed by the recognition of the distinct family Thescelosauridae. This area of the dinosaur family tree has historically been complicated by a lack of research, but papers by Clint Boyd and colleagues<ref name=CABetal09/> and Caleb Brown and colleagues<ref name=CMBetal2011/><ref name=CMBetal13/> have specifically addressed these dinosaurs. Boyd ''et al.'' (2009) and Brown ''et al.'' (2011) found North American "hypsilophodonts" of Cretaceous age to sort into two related clusters, one consisting of ''[[Orodromeus]]'', ''[[Oryctodromeus]]'', and ''[[Zephyrosaurus]]'', and the other consisting of ''Parksosaurus'' and ''Thescelosaurus''.<ref name=CABetal09/><ref name=CMBetal2011/> Brown ''et al.'' (2013) recovered similar results, with the addition of the new genus ''[[Albertadromeus]]'' to the ''Orodromeus'' clade and several long-snouted Asian forms (previously described under [[Jeholosauridae]])<ref name=Hanetal12/> to the ''Thescelosaurus'' clade. They also formally defined Thescelosauridae (''Thescelosaurus neglectus'', ''Orodromeus makelai'', their most recent common ancestor, and all descendants) and the smaller clades Orodrominae and Thescelosaurinae. The below [[cladogram]] is that of Brown ''et al.''.<ref name=CMBetal13>{{cite journal |last=Brown |first=Caleb Marshall |author2=Evans, David C. |author3=Ryan, Michael J. |author4= Russell, Anthony P. |year=2013 |title=New data on the diversity and abundance of small-bodied ornithopods (Dinosauria, Ornithischia) from the Belly River Group (Campanian) of
 
Alberta |journal=Journal of Vertebrate Paleontology |volume=33 |issue=3 |pages=495–520 |doi=10.1080/02724634.2013.746229}}</ref>
 
   
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*In the ''[[Walking with Dinosaurs|Walking With Dinosaurs]]'' episode ''Death of a Dynasty'', a flock of Thescelosaurus were seen drinking from the local river. They were stalked by a hunting ''[[Dromaeosaurus]], ''although ''Thescelosaurus'' would've never met ''Dromaeosaurus'' since ''Dromaeosaurus'' went extinct before the [[K-T Extinction|K-Pg mass extiction]] (although they did encounter raptors like [[Dakotaraptor|''Dakotaraptor'']] and [[Acheroraptor|''Acheroraptor'']]). The theropod ambushed the flock but the ''Thescelosaurus'' scattered and outran the ''Dromaeosaurus''.
{{clade| style=font-size:85%; line-height:85%
 
|label1=[[Thescelosauridae]]
 
|1={{clade
 
|label1=[[Orodrominae]]
 
|1={{clade
 
|1={{clade
 
|1=TMP 2008.045.0002
 
|2=''[[Oryctodromeus]]''}}
 
|2={{clade
 
|1=''[[Albertadromeus]]''
 
|2=''[[Orodromeus]]''
 
|3=''[[Zephyrosaurus]]'' }} }}
 
|label2=[[Thescelosaurinae]]
 
|2={{clade
 
|1=''[[Parksosaurus]]''
 
|2={{clade
 
|1=''[[Changchunsaurus]]''
 
|2=''[[Haya (dinosaur)|Haya]]''
 
|3=''[[Jeholosaurus]]''
 
|4={{clade
 
|1='''''Thescelosaurus assiniboiensis'''''
 
|2='''''Thescelosaurus neglectus''''' }} }} }} }} }}
 
   
  +
*Thescelosaurus was seen at the beginning of the Nova Documentary Arctic Dinosaurs.
==Discovery, history, and species==
 
[[File:Thescelosaurus neglectus.jpg|left|thumb|''T. neglectus'' holotype at the Smithsonian Museum, with skull and neck restored after ''[[Camptosaurus]]'']]
 
The [[holotype|type specimen]] of ''Thescelosaurus'' ([[National Museum of Natural History|USNM]]&nbsp;7757) was discovered in 1891 by [[paleontology|paleontologists]] [[John Bell Hatcher]] and William H. Utterback, from [[stratum|beds]] of the [[Maastrichtian|late Maastrichtian]]-age [[Upper Cretaceous]] [[Lance Formation]] of [[Niobrara County, Wyoming|Niobrara County]] (at the time part of [[Converse County, Wyoming|Converse County]]), [[Wyoming]], [[United States|USA]]. The skeleton, however, remained in its shipping crates for years until [[Charles W. Gilmore]] of the [[Smithsonian Institution]]' [[National Museum of Natural History]] had it prepared and described it in a short paper in 1913, naming it ''T. neglectus'' (''neglectus'': "neglected"). At the time, he thought it was related to ''[[Camptosaurus]]''.<ref name=CWG13>{{cite journal |last=Gilmore |first=Charles W. |authorlink=Charles W. Gilmore |date=May 1913 |title=A new dinosaur from the Lance Formation of Wyoming |journal=Smithsonian Miscellaneous Collections |volume=61 |issue=5 |pages=1–5 |url=http://www.archive.org/details/cbarchive_121329_anewdinosaurfromthelanceformat1862 }}</ref> He provided a detailed [[monograph]] in 1915, describing the well-preserved skeleton.<ref name=CWG15/> The type specimen was found largely in natural articulation and was missing only the head and neck, which were lost due to [[erosion]].<ref name=CWG15/> The name comes from the surprise Gilmore felt at finding such a good specimen that had been unattended to for so long. He considered it to be a light, agile creature, and assigned it to the Hypsilophodontidae, a family of small [[bipedalism|bipedal]] dinosaurs.<ref name=CWG15/>
 
[[File:Gilmorethesc.jpg|thumb|Charles Gilmore's 1915 reconstruction of the ''T. neglectus'' type specimen]]
 
Other remains of similar animals were found throughout the late 19th century and 20th century. Another well-preserved skeleton from the slightly older [[Horseshoe Canyon Formation]], in [[Alberta]], [[Canada]], was named ''T. warreni'' by [[William Parks (paleontologist)|William Parks]] in 1926.<ref name=WAP26>{{cite journal |last=Parks |first=William A |authorlink=William Parks (paleontologist) |year=1926 |title=''Thescelosaurus warreni'', a new species of orthopodous dinosaur from the Edmonton Formation of Alberta |journal=University of Toronto Studies (Geological Series) |volume=21 |pages=1–42 }}</ref> This skeleton had notable differences from ''T. neglectus'', and so [[Charles Mortram Sternberg|Charles M. Sternberg]] placed it in a new genus, ''Parksosaurus'', in 1937.<ref name=CMS37>{{cite journal |last=Sternberg |first=Charles M. |authorlink=Charles Mortram Sternberg |year=1937 |title=Classification of ''Thescelosaurus'', with a description of a new species |journal=Geological Society of America Proceedings for 1936 |pages=365 }}</ref> Sternberg also named an additional species, ''T. edmontonensis'', based on another articulated skeleton, this time including a partial skull ([[Canadian Museum of Nature|NMC]]&nbsp;8537), and drew attention to the genus' heavy build and thick bones. Due to these differences from the regular light hypsilophodont build, he suggested that the genus warranted its own [[Scientific classification|subfamily]], Thescelosaurinae.<ref name=CMS40/> ''T. edmontonensis'' has, since Peter Galton's 1974 review, generally been considered a more robust individual (possibly the [[sexual dimorphism|opposite sex]] of the type individual)<ref name=PMG74/> of ''T. neglectus''.<ref name=NSWC04/><ref name=SN90/> However, Boyd and colleagues found that they could not assign it to either of their valid species of ''Thescelosaurus'' and regarded the specimen as of [[incertae sedis|uncertain placement]] within the genus.<ref name=CABetal09/> The other point of contention regarding ''T. edmontonensis'' is its ankle, which Galton claimed was damaged and misinterpreted, but which was regarded by William J. Morris (1976) as truly different from ''T. neglectus''.<ref name=WJM76/>
 
[[File:Thescelosaurus neglectus, CMN.jpg|thumb|left|Cast of [[Canadian Museum of Nature|CMN]]&nbsp;8537, described as the type specimen for ''T. edmontonensis'' (''T.'' sp. per Boyd ''et al''., [2009])]]
 
In his paper, Morris described a specimen ([[South Dakota School of Mines and Technology|SDSM]]&nbsp;7210) consisting of a partial skull with heavy ridges on the lower jaw and cheek, four partial [[vertebra]]e, and two [[phalanx bones|finger bones]] as an unidentified species of ''Thescelosaurus'', from the late Maastrichtian-age [[Hell Creek Formation]] of [[Harding County, South Dakota|Harding County]], [[South Dakota]], USA. He drew attention to its premaxillary teeth and deeply inset toothline which he interpreted as supporting the presence of muscular cheeks. Morris also pointed out the outwardly flaring premaxilla (which would have given it a wide beak) and large palpebrals.<ref name=WJM76/> This skull was recognized as an unnamed hypsilophodont for many years,<ref name=SN90/> until Galton made it the type specimen of new genus and species ''Bugenasaura infernalis'' ("large-cheeked lizard belonging to the lower regions", ''infernalis'' being a reference to the Hell Creek Formation).<ref name=PMG95>{{cite journal |last=Galton |first=Peter M. |authorlink=Peter Galton |year=1995 |title=The species of the basal hypsilophodontid dinosaur ''Thescelosaurus'' Gilmore (Ornithischia: Ornithopoda) from the Late Cretaceous of North America |journal=Neues Jahrbuch fèur Geologie und Paläontologie Abhandlungen |volume=198 |issue=3 |pages=297–311 }}</ref> Morris also named a new possible species of ''Thescelosaurus'' for specimen [[Natural History Museum of Los Angeles County|LACM]]&nbsp;33542: ?''T. garbanii'' (with a question mark because he was uncertain that it belonged to the genus). LACM&nbsp;33542 comprised a large partial hindlimb ("a third larger than described specimens of ''T. neglectus'' and ''[[Parksosaurus]]'' or nearly twice as large as ''[[Hypsilophodon]]''") including a foot, [[tarsus (skeleton)|tarsus]], shin bones, and partial thigh bone, along with five cervical (neck) and eleven dorsal (back) vertebrae, from the Hell Creek Formation of [[Garfield County, Montana|Garfield County]], [[Montana]], USA. The specimen was discovered by amateur [[paleontology|paleontologist]] [[Harley Garbani]], hence the name. ''T. garbanii'' would have been about 4.5&nbsp;meters (15&nbsp;feet) long, greater than average specimens of ''T. neglectus''. Aside from the size, Morris drew attention to the way the ankle was constructed, which he considered to be unique except in comparison with ''Thescelosaurus edmontonensis'', which he regarded as a separate species. Because Morris believed that the ankles of ''T. garbanii'' compared favorably to those of ''T. edmontonensis'', he tentatively assigned it to ''Thescelosaurus''.<ref name=WJM76/> However, the scientific literature has favored Galton's view that ''T. edmontonensis'' was not different from ''T. neglectus'' (see above). In the same paper that he described ''Bugenasaura'', Galton demonstrated that the features Morris had thought connected ''T. garbanii'' and ''T. edmontonensis'' were the result of damage to the latter's ankle, so ''T. garbanii'' could also be considered distinct from ''Thescelosaurus''. To better accommodate this species, Galton suggested that it belonged to his new genus ''Bugenasaura'' as ''B. garbanii'', although he also noted that it could be belong to the similarly sized [[Pachycephalosauria|pachycephalosaurid]]'' [[Stygimoloch]]'', or be part of a third, unknown dinosaur.<ref name=PMG95/>
 
[[File:Thescelosaurus neglectus (1).jpg|thumb|''Thescelosaurus'' specimen in Museum of the Rockies]]
 
Clint Boyd and colleagues published a reassessment of ''Thescelosaurus'', ''Bugenasaura'', and ''Parksosaurus'' in 2009, using new cranial material as a starting point. They found that ''Parksosaurus'' was indeed distinct from ''Thescelosaurus'', and that the skull of ''Bugenasaura infernalis'' was essentially the same as a skull found with a postcranial skeleton that matched ''Thescelosaurus''. Because ''B infernalis'' could not be differentiated from ''Thescelosaurus'', they regarded the genus as a synonym of ''Thescelosaurus'', the species as [[nomen dubium|dubious]], and SDSM&nbsp;7210 as an example of ''T.'' sp. They found that LACM&nbsp;33542, although fragmentary, was a specimen of ''Thescelosaurus'', and agreed with Morris that the ankle structure was distinct, returning it to ''T. garbanii''. Finally, they noted that another specimen, [[Royal Saskatchewan Museum|RSM]]&nbsp;P.1225.1, differed from ''T. neglectus'' in some anatomical details, and may represent a new species. Thus, ''Thescelosaurus'' per Boyd et al. (2009) is represented by at least two, and possibly three valid species: type species ''T. neglectus'', ''T. garbanii'', and a possible unnamed species.<ref name=CABetal09/> In December [[2011 in paleontology|2011]], RSM&nbsp;P.1225.1 was assigned to its own species, ''Thescelosaurus assiniboiensis''. It was named by Caleb M. Brown, Clint A. Boyd and Anthony P. Russell and is known only from its holotype, a small, articulated and almost complete skeleton from the [[Frenchman Formation]] (late Maastrichtian stage) of [[Saskatchewan]].<ref name=CMBetal2011/>
 
   
  +
*It will appear in the upcoming game [[Saurian|''Saurian'']]. It will be portrayed with a mostly feathered body and a scaly tail, head and legs, much like ''[[Kulindadromeus|Kulindadromeus zabaikalicus]]'', although there is no known evidence for ''Thescelosaurus'' having feathers.
==Paleoecology==
 
===Temporal and geographic range===
 
[[File:Thescelosaurus BW.jpg|thumb|''T. neglectus'' reconstruction]]
 
True ''Thescelosaurus'' remains are known definitely only from late [[Maastrichtian]]-age rocks, from Alberta ([[Scollard Formation]]) and Saskatchewan ([[Frenchman Formation]]), Canada, and Wyoming ([[Lance Formation]]), South Dakota ([[Hell Creek Formation]]), Montana (Hell Creek), and [[Colorado]] ([[Laramie Formation]]), USA.<ref name=CABetal09/><ref name=NSWC04/> With the exception of birds, it was one of the last genera of dinosaurs, its remains being found as close as 3&nbsp;meters to the boundary clay containing the [[iridium]] layer that closes the Cretaceous.<ref name=KB86>{{cite journal |doi=10.1080/02724634.1986.10011619 |last=Carpenter |first=Kenneth |authorlink=Kenneth Carpenter |author2=Breithaupt, Brent H. |year=1986 |title=Latest Cretaceous occurrences of nodosaurid ankylosaurs (Dinosauria, Ornithischia) in Western North America and the gradual extinction of the dinosaurs |journal=Journal of Vertebrate Paleontology |volume=6 |issue=3 |pages=251–257 }}</ref> There are reports of teeth from older, [[Campanian]]-age rocks, particularly from the [[Dinosaur Park Formation]] of Alberta,<ref name=AS72>{{cite journal |last=Sahni |first=Ashok |year=1972 |title=The vertebrate fauna of the Judith River Formation, Montana |journal=Bulletin of the American Museum of Natural History |volume=147 |pages=321–412 |id=http://hdl.handle.net/2246/1099 |accessdate=2007-03-10 |url=http://digitallibrary.amnh.org/dspace/bitstream/2246/1099/1/B147a06.pdf |format=free PDF, may not load }}</ref> but these specimens are not from ''Thescelosaurus'' and are much more likely those of ''[[Orodromeus]]''.<ref name=PMG95/> More specimens are known than have been officially described for this genus, such as the Triebold specimen,<ref name=TT/> which has been the source of several skeletal [[casting|casts]] for museums.
 
   
  +
==Gallery==
When Galton revisited ''Thescelosaurus'' and ''Bugenasaura'' in 1999, he described the dentary tooth [[University of California Museum of Paleontology|UCMP]]&nbsp;46911 from the [[Upper Jurassic]] of [[Weymouth, Dorset|Weymouth]], [[England]] as cf. ''Bugenasaura''.<ref name=PMG99/> If it is indeed a tooth from a thescelosaur-like animal, this would significantly extend the [[stratigraphy|stratigraphic]] range of the group.
 
  +
[[Thescelosaurus/Gallery]]
 
===Habitat===
 
Conflicting reports have been made as to its preferred [[habitat (ecology)|habitat]]; two papers suggest it preferred [[river|channels]] to [[floodplain]]s,<ref name=PSJNH02>Pearson, Dean A.; Schaefer, Terry; Johnson, Kirk R.; Nichols, Douglas J.; and Hunter, John P. (2002). "Vertebrate biostratigraphy of the Hell Creek Formation in southwestern North Dakota and northwestern South Dakota". ''The Hell Creek Formation and the Cretaceous-Tertiary Boundary in the Northern Great Plains: An Integrated Continental Record of the End of the Cretaceous.'' 145–167.</ref><ref name=TLNL11>{{cite journal |last=Lyson |first=Tyler R. |author2=Longrich, Nicholas R. |year=2011 |title=Spatial niche partitioning in dinosaurs from the latest Cretaceous (Maastrichtian) of North America |journal=Proceedings of the Royal Society B |pmid=20943689 |volume=278 |doi=10.1098/rspb.2010.1444 |issue=1709 |pages=1158–1164 |pmc=3049066}}</ref> but another suggests it preferred the opposite.<ref name=KY02>{{cite journal |last=Carpenter |first=Kenneth |authorlink=Kenneth Carpenter |author2=and Young |author3=D. Bruce |title=Late Cretaceous dinosaurs from the Denver Basin, Colorado |journal=Rocky Mountain Geology |year=2002 |volume=37 |issue=2 |pages=237–254 |doi=10.2113/11}}</ref> The possible preference for channels is based on the relative abundance of thescelosaur fossils in [[sandstone]]s, representing channel environments, in comparison to [[mudstone]]s, representing floodplain environments.<ref name=TLNL11/> No [[bone bed|bonebeds]] or accumulations of multiple individuals have yet been reported. [[Dale Russell]], in a popular work, noted that ''Thescelosaurus'' was the most common small herbivore in the [[Hell Creek Formation]] of the [[Fort Peck, Montana|Fort Peck]] area. He described the environment of the time as a flat floodplain, with a relatively dry [[subtropics|subtropical]] climate that supported a variety of plants ranging from [[flowering plant|angiosperm]] trees, to [[Taxodium|bald cypress]], to [[fern]]s and [[ginkgo]]s. Although most dinosaur skeletons from this area are incomplete, possibly due to the low preservation potential of forests, ''Thescelosaurus'' skeletons are much more complete, suggesting that this genus frequented stream channels. Thus when a ''Thescelosaurus'' died, it may have been in or near a river, making it easier to bury and preserve for later fossilization. Russell tentatively compared it to the [[capybara]]s and [[tapir]]s.<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, Inc. |location=Minocqua, Wisconsin |isbn=1-55971-038-1 |pages=175–176 }}</ref> Other dinosaurs that shared its time and place include the [[Ceratopsidae|ceratopsids]] ''[[Triceratops]]'' and ''[[Torosaurus]]'', hadrosaurid ''[[Edmontosaurus]]'', [[Ankylosauridae|ankylosaurid]] ''[[Ankylosaurus]]'', [[pachycephalosauria]]n ''[[Pachycephalosaurus]]'', and the [[Theropoda|theropods]] ''[[Ornithomimus]]'', ''[[Troodon]]'', and ''[[Tyrannosaurus]]''.<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". ''The Dinosauria'' (2nd). 517–606.</ref><ref name=HCFF>{{cite web | author = Bigelow, Phillip | title = Cretaceous "Hell Creek Faunal Facies"; Late Maastrichtian | url= http://www.scn.org/~bh162/hellcreek2.html | accessdate = 2007-01-26 }}</ref> ''Thescelosaurus'' was also abundant in the Lance Formation. Toe bones from this genus are the most common finds after fossils of ''Triceratops'' and ''Edmontosaurus'', and it may have been the most common dinosaur there in life, if the Lance Formation had a preservational bias against small animals.<ref name=KD94>{{cite book |last=Derstler |first=Kraig |year=1994 |editor=Nelson, Gerald E. (ed.) |title=The Dinosaurs of Wyoming |series=Wyoming Geological Association Guidebook, 44th Annual Field Conference |chapter=Dinosaurs of the Lance Formation in eastern Wyoming |publisher=Wyoming Geological Association |pages=127–146}}</ref>
 
 
==Paleobiology==
 
''Thescelosaurus'' would have [[Herbivory|browsed]] in the first meter or so from the ground, feeding selectively,<ref name=NSWC04/> with food held in the mouth by [[cheek]]s while [[mastication|chewing]].<ref name=PMG74>{{cite journal |last=Galton |first=Peter M. |authorlink=Peter Galton |year=1974 |title=Notes on ''Thescelosaurus'', a conservative ornithopod dinosaur from the Upper Cretaceous of North America, with comments on ornithopod classification |journal=Journal of Paleontology |volume=48 |issue=5 |pages=1048–1067 }}</ref> ''Thescelosaurus'' was probably slower than other hypsilophodonts, because of its heavier build and leg structure. Compared to them, it had unusual hindlimbs, because the [[femur|upper leg]] was longer than the [[tibia|shin]], the opposite of ''[[Hypsilophodon]]'' and running animals in general.<ref name=CMS40/> One specimen is known to have had a bone [[pathology]], with the [[metatarsus|long bones]] of the right foot fused at their tops, hindering swift movement.<ref name=BRE03a>{{cite book |last=Erickson |first=Bruce R. |authorlink=Bruce Erickson (paleontologist)|title=Dinosaurs of the Science Museum of Minnesota |year=2003 |publisher=The Science Museum of Minnesota |location=St. Paul, Minnesota |pages=31–32 }}</ref>
 
 
==="Heart of stone"===
 
[[File:Willo.jpg|thumb|"Willo" specimen, with the possible heart left of the [[shoulder blade]]]]
 
In 2000, a skeleton of this genus informally known as "Willo", now on display at the [[North Carolina Museum of Natural Sciences]], was described as including the remnants of a four-chambered heart and an [[aorta]]. It had been originally unearthed in 1993 in northwestern South Dakota. The authors had found the internal detail through [[computed tomography]] (CT) imagery. They suggested that the heart had been [[saponification|saponified]] (turned to [[adipocere|grave wax]]) under [[wikt:anaerobic|airless]] burial conditions, and then changed to [[goethite]], an [[iron|iron mineral]], by replacement of the original material. The authors interpreted the structure of the heart as indicating an elevated [[metabolism|metabolic rate]] for ''Thescelosaurus'', not [[reptile|reptilian]] [[Poikilotherm|cold-bloodedness]].<ref name=FRSBHK00/>
 
 
Their conclusions have been disputed; soon after the initial description, other researchers published a paper where they asserted that the heart is really a [[concretion]]. As they noted, the anatomy given for the object is incorrect (for example, the "aorta" narrows coming into the "heart" and lacks [[artery|arteries]] coming from it), it partially engulfs one of the ribs and has an internal structure of concentric layers in some places, and another concretion is preserved behind the right leg.<ref name=RMS01>{{cite journal |last=Rowe |first=Timothy |author2=McBride, Earle F. |author3= Sereno, Paul C. |date=February 2001 |title=Technical comment: dinosaur with a heart of stone |journal=Science |volume=291 |issue=5505 |pages=783a |doi=10.1126/science.291.5505.783a |url=http://www.sciencemag.org/cgi/content/full/291/5505/783a |accessdate=2007-03-10 |pmid=11157158 }}</ref> The original authors defended their position; they agreed that it was a type of concretion, but one that had formed around and partially preserved the more muscular portions of the heart and aorta.<ref name=RFBS01>{{cite journal |last=Russell |first=Dale A. |authorlink=Dale Russell |author2=Fisher, Paul E. |author3=Barrick, Reese E. |author4= Stoskopf, Michael K. |date=February 2001 |title=Reply: dinosaur with a heart of stone |journal=Science |volume=291 |issue=5505 |pages=783a |doi=10.1126/science.291.5505.783a |url=http://www.sciencemag.org/cgi/content/full/291/5505/783a |accessdate=2007-03-10 |pmid=11157158 }}</ref>
 
 
A study published in 2011 applied multiple lines of inquiry to the question of the object's identity, including more advanced CT scanning, [[histology]], [[X-ray scattering techniques|X-ray diffraction]], [[X-ray photoelectron spectroscopy]], and [[scanning electron]] microscopy. From these methods, the authors found the following: the object's internal structure does not include chambers but is made up of three unconnected areas of lower density material, and is not comparable to the structure of an [[ostrich]]'s heart; the "walls" are composed of [[sedimentary]] minerals not known to be produced in biological systems, such as goethite, [[feldspar]] minerals, [[quartz]], and [[gypsum]], as well as some plant fragments; [[carbon]], [[nitrogen]], and [[phosphorus]], [[chemical element]]s important to life, were lacking in their samples; and cardiac cellular structures were absent. There was one possible patch with animal cellular structures. The authors found their data supported identification as a concretion of sand from the burial environment, not the heart, with the possibility that isolated areas of tissues were preserved.<ref name=TCetal11>{{cite journal |last=Cleland |first=Timothy P. |author2=Stoskopf, Michael K. |author3= Schweitzer, Mary H. |title=Histological, chemical, and morphological reexamination of the "heart" of a small Late Cretaceous ''Thescelosaurus'' |journal=Naturwissenschaften |year=2011 |volume=98 |doi=10.1007/s00114-010-0760-1 |issue=3 |pages=203–211 |pmid=21279321|bibcode = 2011NW.....98..203C }}</ref>
 
 
The question of how this find reflects metabolic rate and dinosaur internal anatomy is moot, though, regardless of the object's identity.<ref name=TCetal11/> Both modern [[crocodilia]]ns and [[bird]]s, the closest living relatives of dinosaurs, have four-chambered hearts (albeit modified in crocodilians), so dinosaurs probably had them as well; the structure is not necessarily tied to metabolic rate.<ref name=CH04>Chinsamy, Anusuya; and Hillenius, Willem J. (2004). "Physiology of nonavian dinosaurs". ''The Dinosauria'', 2nd ed. 643–659.</ref>
 
 
== In popular culture ==
 
[[File:Thescelosaurus_from_were_back.jpg|thumb]]A Thescelosaurus had a cameo in the 1993 movie [[We're Back! A Dinosaur's Story]], In ''Walking With Dinosaurs'', the episode ''Death of a Dynasty'', A flock of Thescelosaurus were seen drinking from the local river. They were stalked by a hunting Dromaeosaurus. The theropod ambushed the flock but the Thescelosaurus scattered and outran the Dromaeosaurus.
 
 
[[Category:Ornithopods]]
 
[[Category:Ornithopods]]
 
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[[Category:Herbivores]]
 
[[Category:Cretaceous dinosaurs]]
 
[[Category:Cretaceous dinosaurs]]
[[Category:We're Back A Dinosaur's Story Characters]]
 
 
[[Category:Cretaceous extinctions]]
 
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[[Category:Dinosaurs from Hell Creek]]
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Revision as of 00:19, 5 September 2019

Thescelosaurus
Thesc
Thescelosaurus restored with a smooth coat of protofeathers
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
clade: Dinosauria
Order: Ornithischia
Suborder: Ornithopoda
Family: Thescelosauridae
Genus: Thescelosaurus
Gilmore et al., 1913
Species: T. neglectus
Binomial name
Thescelosaurus neglectus
Gilmore et al., 1913

Thescelosaurus (/ˌθɛsᵻləˈsɔːrəs/ thess-il-ə-sor-əs; ancient Greek θέσκελος-/theskelos- meaning "godlike", "marvelous", or "wondrous" and σαυρος/sauros "lizard")[2] was a genus of small ornithopod dinosaur that appeared at the very end of the Late Cretaceous period in North America. It was a member of the last dinosaurian fauna before the Cretaceous–Paleogene extinction event around 66 million years ago. The preservation and completeness of many of its specimens indicate that it may have preferred to live near streams.

This bipedal ornithopod is known from several partial skeletons and skulls that indicate it grew to between 2.5 and 4.0 meters (8.2 to 13.1 ft) in length on average. It had sturdy hind limbs, small wide hands, and a head with an elongate pointed snout. The form of the teeth and jaws suggest a primarily herbivorous animal. This genus of dinosaur is regarded as a specialized basal ornithopod, traditionally described as a hypsilophodont, but more recently recognized as distinct from Hypsilophodon. Several species have been suggested for this genus. Three currently are recognized as valid: the type species T. neglectus, T. garbanii and T. assiniboiensis.

The genus attracted media attention in 2000, when a specimen unearthed in 1993 in South Dakota, United States, was interpreted as including a fossilized heart. There was much discussion over whether the remains were of a heart. Many scientists now doubt the identification of the object and the implications of such an identification.

Description

Thescelosaurus was a heavily built bipedal animal, probably herbivorous, but potentially not.[3] There was a prominent ridge along the length of both maxillae (the tooth-bearing "cheek" bones),[1] and a ridge on both dentaries (tooth-bearing bone of the lower jaw).[4] The ridges[4] and position of the teeth, deeply internal to the outside surface of the skull, are interpreted as evidence for muscular cheeks.[5] Aside from the long narrow beak, the skull also had teeth in the premaxilla, or upper beak (a primitive trait among ornithopods).[6] Long rod-like bones called palpebrals were present over the eyes, giving the animal heavy bony eyebrows.[6] Its teeth were of two types: small pointed premaxillary teeth, and leaf-shaped cheek teeth.[7] Six small teeth were present in both premaxillae, with a toothless section at the tip of the beak.[1]

Thescelosaurs had short, broad, five-fingered hands, four-toed feet with hoof-like toe tips, and a long tail braced by ossified tendons from the middle to the tip, which would have reduced the flexibility of the tail.[8] The rib cage was broad, giving it a wide back, and the limbs were robust.[7] The animals may have been able to move on all fours, given its fairly long arms and wide hands,[9] but this idea has not been widely discussed in the scientific literature, although it does appear in popular works.[10][11] Charles M. Sternberg reconstructed it with the upper arm oriented almost perpendicular to the body,[7] another idea that has gone by the wayside. As noted by Peter Galton, the upper arm bone of most ornithischians articulated with the shoulder by an articular surface that consisted of the entire end of the bone, instead of a distinct ball and socket as in mammals. The orientation of the shoulder's articular surface also indicates a vertical and not horizontal upper arm in dinosaurs.[12]

Large thin flat mineralized plates have been found next to the ribs' sides.[13] Their function is unknown; they may have played a role in respiration.[14] However, muscle scars or other indications of attachment have not been found for the plates, which argues against a respiratory function. Recent histological study of layered plates from a probable subadult indicates that they may have started as cartilage and became bone as the animal aged.[15] Such plates are known from several other ornithopods and their cerapodan relatives.

The nature of this genus' integument, be it scales or something else, is currently unknown, although potential evidence exists: Charles Gilmore described patches of carbonized material near the shoulders as possible epidermis, with a "punctured" texture, but no regular pattern,[8] and William J. Morris suggested that armor was present, in the form of small scutes he interpreted as located at least along the midline of the neck of one specimen.[5] Scutes have not been found with other articulated specimens of Thescelosaurus, though, and Morris's scutes could be crocodilian in origin.[16]

Overall, the skeletal anatomy of this genus is well documented, and restorations have been published in several papers, including skeletal restorations[1][8][9][17] and models.[7][8] The skeleton is known well enough that a detailed reconstruction of the hip and hindlimb muscles has been made.[18] The animal's size has been estimated in the 2.5–4.0 m range for length (8.2–13.1 ft)[9] for various specimens, and a weight of 200–300 kilograms (450–660 pounds),[19] with the large type specimen of T. garbanii estimated at 4–4.5 meters (13.1–14.8 feet) long.[5] As discussed more fully under "Discovery, history, and species", it may have been sexually dimorphic, with one sex larger than the other.[9] Juvenile remains are known from several locations, mostly based on teeth.

In popular culture

  • In the Walking With Dinosaurs episode Death of a Dynasty, a flock of Thescelosaurus were seen drinking from the local river. They were stalked by a hunting Dromaeosaurus, although Thescelosaurus would've never met Dromaeosaurus since Dromaeosaurus went extinct before the K-Pg mass extiction (although they did encounter raptors like Dakotaraptor and Acheroraptor). The theropod ambushed the flock but the Thescelosaurus scattered and outran the Dromaeosaurus.
  • Thescelosaurus was seen at the beginning of the Nova Documentary Arctic Dinosaurs.
  • It will appear in the upcoming game Saurian. It will be portrayed with a mostly feathered body and a scaly tail, head and legs, much like Kulindadromeus zabaikalicus, although there is no known evidence for Thescelosaurus having feathers.

Gallery

Thescelosaurus/Gallery