Thescelosaurus

Taxobox
name = "Thescelosaurus"
fossil_range = Late Cretaceous

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image_width = 250px
image_caption = "Thescelosaurus neglectus"
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Ornithischia
subordo = Cerapoda
infraordo = Ornithopoda
familia = Hypsilophodontidae
subfamilia = Thescelosaurinae
genus = "Thescelosaurus"
genus_authority = Gilmore, 1913
subdivision_ranks = Species
subdivision =
* "T. neglectus" Gilmore, 1913 (type)

"Thescelosaurus" (pronEng|ˌθɛsɪləˈsɔrəs, from the Greek θεσκελο-/"thescelo-" meaning "godlike", "marvelous", or "wondrous" and σαυρος/"saurus" "lizard") [ cite book|author=Liddell & Scott|year=1980|title=Greek-English Lexicon, Abridged Edition |publisher=Oxford University Press, Oxford, UK|id=ISBN 0-19-910207-4] 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-Tertiary extinction event around 65.5 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, a head with an elongate pointed snout, and possibly small armor scutes along the midline of the back. This genus of dinosaur is regarded as a specialized hypsilophodont and a herbivore. Several species have been suggested for this genus, but only one, "T. neglectus", is currently recognized; the others have been given their own genera, or are believed to be the same as "T. neglectus" (although there may be more than one species represented by the various fossils classified as "Thescelosaurus").

The genus attracted media attention in 2000, when a specimen unearthed in 1993 in South Dakota was interpreted as including a fossilized heart. There was much discussion over whether the remains were actually 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,cite book |last=Norman |first=David B. |authorlink=David B. Norman |coauthors=Sues, Hans-Dieter; Witmer, Larry M.; and 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] but possibly omnivorous.cite web | author = Triebold Paleontology, Inc. | title = Thescelosaurus | url= http://www.trieboldpaleontology.com/casts/thescelosaurus_new.htm | accessdate = 2007-01-26 ] It would have browsed in the first meter or so from the ground, feeding selectively, with food held in the mouth by cheeks while chewing.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 ] Aside from the long narrow beak, the skull also had teeth in the premaxilla, or upper beak (a primitive trait among ornithopods), and long rod-like bones called palpebrals over the eyes, giving it heavy bony eyebrows.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 ] Its teeth were of two types: small pointed premaxillary teeth, and leaf-shaped cheek teeth.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 ] The exact number of teeth is unknown, as complete jaws have not been described. It 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 back to the tip, which would have reduced the flexibility of the tail.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 ] The rib cage was broad, giving it a wide back, and the limbs were robust. This animal may have been able to move on all fours, given its fairly long arms and wide hands, but this idea has not been followed up in the scientific literature (although it does appear in popular works).cite book |last=Lambert |first=David |coauthors=and the Diagram Group |title=The Dinosaur Data Book |year=1990 |publisher=Avon Books |location=New York |isbn=0-380-75896-3 |chapter=Thescelosaurids |pages=p. 153] cite book|title=The Dinosaur Society Dinosaur Encyclopedia|year=1993 |last=Lessem |first=Donald |authorlink=Don Lessem |coauthors= and Glut, Donald F. |pages=p. 475 |publisher=Random House, Inc.|id=ISBN 0-679-41770-2] Charles M. Sternberg reconstructed it with the upper arm sticking out almost perpendicular to the body, 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.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 ] "Thescelosaurus" was probably slower than other hypsilophodonts, because of its heavier build and leg structure. Compared to them, it had unusual hindlimbs, because the upper leg was longer than the shin, the opposite of "Hypsilophodon" and running animals in general. One specimen is known to have had a bone pathology, with the long bones of the right foot fused at their tops, hindering swift movement.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 |isbn=911338-54-3 |pages=31–32 ] Large thin flat mineralized plates have been found next to the ribs' sides.cite journal |last=Fisher |first=Paul E. |coauthors=Russell, Dale A.; Stoskopf, Michael K.; Barrick, Reese E.; Hammer, Michael; and Kuzmitz, Aandrew A. |year=2000 |month=April |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 ] Their function is unknown; they may have played a role in respiration.cite journal |last=Novas |first=Fernando E. |coauthors=Cambiaso, Andrea V; and 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 ] 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.cite journal |last=Boyd |first=Clint A. |coauthors=and 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] Such plates are known from several other ornithopods and their cerapodan relatives.cite journal |last=Butler |first=Richard J. |coauthors=and 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]

The nature of this genus' integument, be it scales or something else, is currently unknown, although potential evidence is known; Charles Gilmore described patches of carbonized material near the shoulders as possible epidermis, with a "punctured" texture but no regular pattern, and William J. Morris suggested that armor was present, in the form of small scutes present at least along the midline of the neck of one specimen.cite book |last=Morris |first=William J. |editor=Churcher, C.S. (ed.) |title=Athlon |year=1976 |publisher=Royal Ontario Museum |location=Toronto |isbn=0888541570 |pages=93–113 |chapter=Hypsilophodont dinosaurs: a new species and comments on their systematics] Scutes have not been found with other articulated specimens of "Thescelosaurus", though, and Morris's scutes could be crocodilian in origin.

Overall, the skeletal anatomy of this genus is well-documented (except for the head), and restorations have been published in several papers, including skeletal restorationscite 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 ] and models. The skeleton is known well enough that a detailed reconstruction of the hip and hindlimb muscles has been made.cite journal |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 ] The animal's size has been estimated in the 2.5–4.0 m range for length (8.2–13.1 ft) for various specimens, and a weight of 200–300 kilograms (450–660 pounds).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 |isbn=911338-54-3 |pages=p. 31 ] As discussed more fully under "Discovery, history, and species," it may have been sexually dimorphic, with one sex larger than the other. Juvenile remains are known from several locations, mostly based on teeth.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 |url=https://scientists.dmns.org/sites/kencarpenter/PDFs%20of%20publications/baby%20teeth.pdf |accessdate=2007-03-10 ] cite book |last=Russell |first=Dale A. |authorlink=Dale Russell |coauthors=and 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 ]

Classification

clade| style=font-size:100%;line-height:80%
label1=Euornithopoda
1=clade
1="Orodromeus"
2="Othnielosaurus"
label3=unnamed
3=clade
label1=unnamed
1=clade
1="Gasparinisaura"
2="Hypsilophodon"
3="Zephyrosaurus"
label2=unnamed
2=clade
label1=unnamed
1=clade
1=?"Bugenasaura"
2="Parksosaurus"
3="Thescelosaurus"
2=Iguanodontia

This cladogram is based on Norman "et al." (2004), with the results of the very similar cladogram from Weishampel "et al." (2003) used to clarify the position of Iguanodontia, which was left out of Norman "et al." The group consisting of "Bugenasaura", "Parksosaurus", and "Thescelosaurus" is roughly what modern informal usage of Thescelosaurinae corresponds to.
"Thescelosaurus" has generally been allied to "Hypsilophodon" and other small ornithopods as a hypsilophodontid, although recognized as being distinct among them for its robust build, unusual hindlimbs, and, more recently, its unusually long skull.cite book |last=Sues |first=Hans-Dieter |coauthors=and 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] 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 Iguanodontidae. This has not been followed, with Morris arguing strongly against Galton's classification scheme. At any rate, Galton's Iguanodontidae was not a natural group due to polyphyly, and so would not be recognized under modern cladistic usage.

Although little tested by cladistics, it is currently thought that "Bugenasaura" and "Thescelosaurus" are closely related,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 ] or that "Thescelosaurus" belongs in its own family or subfamily, Thescelosauridae or Thescelosaurinae.cite book |last= Holtz |first=Thomas R., Jr. |authorlink=Thomas R. Holtz Jr. |editor=Paul, Gregory S. (ed.) |title=The Scientific American Book of Dinosaurs |year=2000 |publisher=St. Martin's Press |location=New York |isbn=0-312-26226-4 |pages=140–168 |chapter=Classification and Evolution of the Dinosaur Groups ] cite journal |last=Carpenter |first=Kenneth |authorlink=Kenneth Carpenter |coauthors=and Young, D. Bruce |title=Late Cretaceous dinosaurs from the Denver Basin, Colorado |journal=Rocky Mountain Geology |year=2002 |volume=37 |issue=2 |pages=237–254 |url=https://scientists.dmns.org/sites/kencarpenter/PDFs%20of%20publications/Denver%20dinos.pdf |accessdate=2007-03-10 ] Two recent studies have found it to be a close relative of "Parksosaurus", although neither named a specific clade, and one of the studies (Norman "et al.", 2004) is difficult to interpret because it did not include Iguanodontia in its diagrams.cite journal |last=Weishampel |first= David B. |authorlink=David B. Weishampel |coauthors=Jianu, Coralia-Maria; Csiki, Z.; and 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 ] This area of the dinosaur family tree is complicated by a lack of research, with some papers finding Hypsilophodontidae to be a natural group,cite journal |last=Weishampel |first=David B. |authorlink=David B. Weishampel |coauthors=and 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 |accessdate=2007-03-10 ] and others finding it to be a unnatural family leading into Iguanodontia (paraphyly).cite journal |last=Varricchio |first=David J. |coauthors=Martin, Anthony J.; and 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 |volume=274 |pages=1361–1368 |doi=10.1098/rspb.2006.0443 |url=http://journals.royalsociety.org/content/uj1k12wh01587821/fulltext.pdf |accessdate=2007-03-22 ] The "natural group" hypothesis has been falling out of favor since the mid to late 1990s, and thus a paraphyletic Hypsilophodontidae is shown here. Oddly, "Thescelosaurus" has been regarded as both very basal and very derived among the hypsilophodonts. One issue specifically concerning "Thescelosaurus" is that not all of the remains assigned to "T. neglectus" necessarily belong to it.cite journal |last=Butler |first=Richard J. |coauthors=Upchurch, Paul; and 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]

Discovery, history, and species

The type specimen of "Thescelosaurus" (USNM 7757) was discovered in 1891 by paleontologists John Bell Hatcher and William H. Utterback, from beds of the late Maastrichtian-age Upper Cretaceous Lance Formation of Niobrara County (at the time part of Converse County), Wyoming, 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".cite journal |last=Gilmore |first=Charles W. |authorlink=Charles W. Gilmore |year=1913 |month=May |title=A new dinosaur from the Lance Formation of Wyoming |journal=Smithsonian Miscellaneous Collections |volume=61 |issue=5 |pages=1–5 ] He provided a detailed monograph in 1915, describing the well-preserved skeleton. The type specimen was found largely in natural articulation and was missing only the head and neck, which were lost due to erosion. 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 bipedal dinosaurs.

Other remains of similar animals were found throughout the late 1800s and 1900s, although they did not receive much attention. Another well-preserved skeleton from the slightly older Horseshoe Canyon Formation, in Alberta, Canada, was named "T. warreni" by William Parks in 1926.cite journal |last=Parks |first=William A |authorlink=William Parks |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 ] This skeleton had notable differences from "T. neglectus", and so Charles M. Sternberg placed it in a new genus, "Parksosaurus", in 1937.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=p. 365 ] Sternberg also named an additional species, "T. edmontonensis", based on another articulated skeleton, this time including a partial skull (NMC 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 subfamily, Thescelosaurinae. "T. edmontonensis" has, since Peter Galton's 1974 review, generally been considered a more robust individual (possibly the opposite sex of the type individual) of "T. neglectus". The only sticking point has been the ankle of "T. edmontonensis", which Galton claimed was damaged and misinterpreted, but which was accepted by William J. Morris (1976) as truly different from "T. neglectus".In his paper, Morris described a partial skull with heavy ridges on the lower jaw and cheek (SDSM 7210) as an unidentified species of "Thescelosaurus", from the late Maastrichtian-age Hell Creek Formation of Harding County, South Dakota, USA. This skull was recognized as an unnamed hypsilophodont for many years, until Galton assigned it the name "Bugenasaura infernalis".cite journal |last=Galton |first=Peter M. |authorlink=Peter M. 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 ] Morris also named a new species, on the basis of vertebrae and limb remains (LACM 33542) from the Hell Creek Formation of Garfield County, Montana, USA: "T. garbanii". "T. garbanii" would have been about 4.5 m long (15 feet), larger than average specimens of "T. neglectus". Because Morris believed that the ankles of "T. garbanii" compared favorably to those of "T. edmontonensis", he assigned it to "Thescelosaurus". However, the scientific literature has favored Galton's view that "T. edmontonensis" was not different from "T. neglectus" (see above). To better accommodate this species, Galton in 1995 suggested that it belonged to his new genus "Bugenasaura" as "B. garbanii" (although noting that it could also be a leg of the similarly sized pachycephalosaurid" Stygimoloch"). As a result, only one valid species of "Thescelosaurus" is currently recognized: "T. neglectus". More study, though, could again split the known material into two or more species.

Paleoecology

Temporal and geographic range

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. With the exception of birds, it was one of the last extant genera of dinosaurs, its remains being found as close as 3 meters to the boundary clay containing the iridium layer that closes the Cretaceous.cite journal |last=Carpenter |first=Kenneth |authorlink=Kenneth Carpenter |coauthors=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 |url=https://scientists.dmns.org/sites/kencarpenter/PDFs%20of%20publications/NodoExtinct.pdf |accessdate=2007-03-10 ] There are reports of teeth from older, Campanian-age rocks, particularly from the Dinosaur Park Formation of Alberta,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 ] but these specimens are not from "Thescelosaurus" and are much more likely those of "Orodromeus". More specimens are known than have been officially described for this genus, such as "Willo", with its complete skull, and the Triebold specimen, which has been the source of several skeletal casts for museums.

Habitat

Conflicting reports have been made as to its preferred habitat; one paper suggests it preferred channels to floodplains,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.] but another suggests it preferred the opposite. No 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 area. He described the environment of the time as a flat floodplain, with a relatively dry subtropical climate that supported a variety of plants ranging from angiosperm trees, to cedar and bald cypress, to ferns and ginkgos. 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 capybaras and tapirs.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 ] Other dinosaurs that shared its time and place include "Bugenasaura", the ceratopsids "Triceratops" and "Torosaurus", hadrosaurids "Edmontosaurus" and "Anatotitan", ankylosaurid "Ankylosaurus", pachycephalosaurians "Pachycephalosaurus" and "Stygimoloch", and the theropods "Ornithomimus", "Troodon", and "Tyrannosaurus".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.] cite web | author = Phillip Bigelow | title = Cretaceous "Hell Creek Faunal Facies"; Late Maastrichtian | url= http://www.scn.org/~bh162/hellcreek2.html | accessdate = 2007-01-26 ] "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, if the Lance Formation had a preservation bias against small animals.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]

Paleobiology

"Heart of stone"

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 imagery. They suggested that the heart had been saponified (turned to grave wax) under burial conditions, and then changed to goethite, an iron mineral, by replacement of the original material. The authors interpreted the structure of the heart as indicating an elevated metabolic rate for "Thescelosaurus", not reptilian cold-bloodedness.

Their conclusions have been disputed; other researchers published a paper where they assert that the heart is really a concretion. As they note, the anatomy given for the object is incorrect (for example, the "aorta" narrows coming into the "heart" and lacks 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.cite journal |last=Rowe |first=Timothy |coauthors=McBride, Earle F.; and Sereno, Paul C. |year=2001 |month=February |title=Technical comment: dinosaur with a heart of stone |journal=Science |volume=291 |issue=5505 |pages=p. 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 ] 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.cite journal |last=Russell |first=Dale A. |authorlink=Dale Russell |coauthors=Fisher, Paul E.; Barrick, Reese E.; and Stoskopf, Michael K. |year=2001 |month=February |title=Reply: dinosaur with a heart of stone |journal=Science |volume=291 |issue=5505 |pages=p. 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 ] The question of how this find reflects on metabolic rate and dinosaur internal anatomy may be moot, though, regardless of the object's identity. Both modern crocodilians and birds, 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.Chinsamy, Anusuya; and Hillenius, Willem J. (2004). "Physiology of nonavian dinosaurs". "The Dinosauria", 2nd. 643–659.]

In popular culture

"Thescelosaurus", despite being known from better remains than many dinosaurs, is an uncommon genus in children's books and general dinosaur books, although it may be highlighted in more comprehensive field guides and encyclopedias due to its differences from other hypsilophodonts.cite book |last=Lambert |first=David |coauthors=and the Diagram Group |title=A Field Guide to Dinosaurs |year=1983 |publisher=Avon Books |location=New York |isbn=0-380-83519-3 |chapter= Thescelosaurids |pages=p. 149] Books since the scientific publication of "Willo"'s possible heart have incorporated the initial reports, but because these events are still relatively recent, the entire controversy is not necessarily included.cite book |first= Dougal |last=Dixon |authorlink=Dougal Dixon |year=2006 |title=The Complete Book of Dinosaurs |publisher=Anness Publishing Ltd. |location=London |pages=212–213 |isbn= 0-681-37578-7 ]

Despite its reputation among professionals for lacking speed and agility, "Thescelosaurus" has been a featured animal in a mathematical modeling problem given to undergraduate students, based around the question of what the best hunting strategy is for one or two pursuing "Velociraptor" hunting a "Thescelosaurus" which, due to its bony structure, has a much shorter turning radius.cite web | author = Amrita Das | title = The Hunting Strategy of the Velociraptor — Amrita Das | url= http://web.archive.org/web/20070602204445/http://www.iusb.edu/~journal/1999/Paper4.html | accessdate = 2007-12-16 ] cite web | author = John David Stone | title = Mathematical Contest in Modeling, 1997 | url= http://www.math.grinnell.edu/mcm-1997.xhtml | accessdate = 2007-01-29]

References

External links

* [http://www.dinoheart.org Willo, the Dinosaur with a Heart] - The official site for "Willo", from the North Carolina Museum of Natural Sciences.
* [http://www.users.qwest.net/~jstweet1/ornithopoda.htm Ornithopoda at the "Thescelosaurus"! site]
* [http://palaeos.com/Vertebrates/Units/320Ornithischia/500.html#Thescelosaurus "Thescelosaurus" from Palaeos.com] (Technical)