Daspletosaurus 195485 224405513 2008-07-08T18:31:46Z Treisijs 2847625 Adding [[lv:Daspletozaurs]] {{Taxobox | name = ''Daspletosaurus'' | fossil_range = [[Late Cretaceous]] | image = Daspletosaurus FMNH.jpg | image_width = 250px | image_caption = Dinosaur Park ''Daspletosaurus'' specimen, mounted at the [[Field Museum]] in [[Chicago]]. | regnum = [[Animal]]ia | phylum = [[Chordata]] | classis = [[Reptile|Sauropsida]] | superordo = [[Dinosaur]]ia | ordo = [[Saurischia]] | subordo = [[Theropoda]] | familia = [[Tyrannosauridae]] | genus = '''''Daspletosaurus''''' | genus_authority = [[Dale Russell|Russell]], 1970 | subdivision_ranks = [[Species]] | subdivision = *'''''D. torosus''''' ([[Type (zoology)|type]]) <br/><small>Russell, 1970</small> }} '''''Daspletosaurus''''' ({{pronEng|dæsˌpliːtoʊˈsɔrəs}} or das-PLEET-o-''SAWR''-us; meaning 'frightful lizard') is a [[genus]] of [[tyrannosaurid]] [[theropod]] [[dinosaur]] that lived in western [[North America]] between 80 and 73 [[million years ago]], during the Late [[Cretaceous]] [[Period (geology)|Period]]. Fossils of the only named [[species]] (''D. torosus'') were found in [[Alberta]], although other possible species from Alberta, [[Montana]] and [[New Mexico]] await description. Including these undescribed species, ''Daspletosaurus'' is the most species-rich genus of tyrannosaur. ''Daspletosaurus'' is closely related to the much larger and more recent ''[[Tyrannosaurus]]''. Like most known tyrannosaurids, it was a multi-ton [[biped]]al [[predation|predator]] equipped with dozens of large, sharp [[teeth]]. ''Daspletosaurus'' had the small forelimbs typical of tyrannosaurids, although they were proportionately longer than in other genera. As an [[apex predator]], ''Daspletosaurus'' was at the top of the [[food chain]], probably preying on large dinosaurs like the [[ceratopsid]] ''[[Centrosaurus]]'' and the [[hadrosaur]] ''[[Hypacrosaurus]]''. In some areas, ''Daspletosaurus'' coexisted with another tyrannosaurid, ''[[Gorgosaurus]]'', though there is some evidence of [[niche differentiation]] between the two. While ''Daspletosaurus'' fossils are rarer than other tyrannosaurids, the available specimens allow some analysis of the biology of these animals, including [[social behavior]], diet and life history. ==Description== [[Image:Daspletosaurusscale.png|thumb|left|220px|''Daspletosaurus torosus'' with a human for scale.]] While very large by the standard of modern predators, ''Daspletosaurus'' was not the largest tyrannosaurid. Adults could reach a length of 8–9&nbsp;meters (26–30&nbsp;ft) from snout to tail.<ref name=russell1970>{{cite_journal |last=Russell |first=Dale A. |authorlink=Dale Russell |year=1970 |title=Tyrannosaurs from the Late Cretaceous of western Canada |journal=National Museum of Natural Sciences Publications in Paleontology |volume=1 |pages=1–34}}</ref> Mass estimates have centered around 2.5&nbsp;[[tonne]]s (2.75&nbsp;[[short ton]]s)<ref name=russell1970/><ref name=paul1988>{{cite_book |last=Paul |first=Gregory S. |authorlink=Gregory S. Paul |year=1988 |title=Predatory Dinosaurs of the World |publisher=Simon & Schuster |location=New York |pages=464pp |isbn=978-0671619466}}</ref><ref name=christiansenfarina2004>{{cite_journal |last=Christiansen |first=Per |coauthors=& Fariña, Richard A. |year=2004 |title=Mass prediction in theropod dinosaurs |journal=Historical Biology |volume=16 |issue=2-4 |pages=85–92 |doi=10.1080/08912960412331284313}}</ref> but have ranged between 1.8&nbsp;tonnes (2&nbsp;tons)<ref name=ericksonetal2004>{{cite_journal |last=Erickson, Gregory M. |coauthors=Makovicky, Peter J.; [[Phil Currie|Currie, Philip J.]]; Norell, Mark A.; Yerby, Scott A.; & Brochu, Christopher A. |year=2004 |title=Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs |journal=Nature |volume=430 |pages=772–775 |doi=10.1038/nature02699}}</ref> and 3.8&nbsp;tonnes (4.1&nbsp;tons).<ref name=therrienhenderson2007>{{cite_journal |last=Therrien |first=François |coauthors=& Henderson, Donald M. |year=2007 |title=My theropod is bigger than yours... or not: estimating body size from skull length in theropods |journal=Journal of Vertebrate Paleontology |volume=27 |issue=1 |pages=108–115 |url=http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1671%2F0272-4634(2007)27%5B108%3AMTIBTY%5D2.0.CO%3B2&ct=1 |doi=10.1671/0272-4634(2007)27[108:MTIBTY]2.0.CO;2}}</ref> ''Daspletosaurus'' had a massive skull that could reach more than 1&nbsp;meter (3.3&nbsp;ft) in length.<ref name=russell1970/> The bones were heavily constructed and some, including the [[nasal]] bones on top of the snout, were fused for strength. Large [[fenestra]]e (openings) in the skull reduced its weight. An adult ''Daspletosaurus'' was armed with about six dozen teeth that were very long but oval in [[Cross section (geometry)|cross section]] rather than blade-like. Unlike its other teeth, those in the [[premaxilla]] at the end of the upper jaw had a ''D''-shaped cross section, an example of [[heterodonty]] always seen in tyrannosaurids. Unique skull features included the rough outer surface of the [[maxilla]] (upper jaw bone) and the pronounced crests around the eyes on the [[lacrimal]], [[postorbital]], and [[jugal]] bones. The [[Orbit (anatomy)|orbit]] (eye socket) was a tall oval, somewhere in between the circular shape seen in ''Gorgosaurus'' and the 'keyhole' shape of ''Tyrannosaurus''.<ref name=carr1999>{{cite_journal |last=Carr |first=Thomas D. |year=1999 |title=Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria) |journal=Journal of Vertebrate Paleontology |volume=19 |issue=3 |pages=497–520}}</ref><ref name=currie2003a>{{cite_journal |last=Currie |first=Philip J. |authorlink=Phil Currie |year=2003 |title=Cranial anatomy of tyrannosaurids from the Late Cretaceous of Alberta |journal=Acta Palaeontologica Polonica |volume=48 |issue=2 |pages=191–226 |url=http://app.pan.pl/acta48/app48-191.pdf|format=PDF}}</ref><ref name=holtz2004>{{cite_book |last=Holtz |first=Thomas R. |authorlink=Thomas R. Holtz, Jr. |year=2004 |chapter=Tyrannosauroidea |editor= [[David B. Weishampel|Weishampel, David B.]]; [[Peter Dodson|Dodson, Peter]]; & Osmólska, Halszka (eds.). |title=The Dinosauria |edition=Second Edition |publisher=University of California Press |location=Berkeley |pages=111-136 |isbn=0-520-24209-2}}</ref> ''Daspletosaurus'' shared the same body form as other tyrannosaurids, with a short, ''S''-shaped neck supporting the massive skull. It walked on its two thick hindlimbs, which ended in four-toed feet, although the first digit (the [[hallux]]) did not contact the ground. In contrast, the forelimbs were extremely small and bore only two digits, although ''Daspletosaurus'' had the longest forelimbs in proportion to body size of any tyrannosaurid. A long, heavy tail served as a [[counterweight]] to the head and torso, with the [[center of gravity]] over the hips.<ref name=russell1970/><ref name=holtz2004/> ==Classification and systematics== {{userboxtop|align=right|bordercolor=lightgray|toptext=[[Cladistics#Cladograms|Cladograms]] of [[Tyrannosauridae]] highlighting the position of ''Daspletosaurus''}} <br/><u><center>'''[[Thomas Carr (paleontologist)|Carr]] ''et al.'' 2005'''<ref name=carretal2005/></center></u> {{clade| style=font-size:80%;line-height:80% |label1=[[Tyrannosauridae]]&nbsp; |1={{clade |label1=<font color="white">void</font> |1=Albertosaurinae |label2=&nbsp;Tyrannosaurinae&nbsp; |2={{clade |1={{clade |label1=<font color="white">void</font> |1='''''Daspletosaurus''''' |2={{clade |label1=&nbsp;<font color="white">void</font>&nbsp; |1=''[[Tarbosaurus]]''* |2=''[[Tyrannosaurus]]'' }} }} }} }} }} <small>*<u>Note</u>: Carr ''et al.'' use the name ''Tyrannosaurus bataar''</small> <br/><u><center>'''[[Philip Currie|Currie]] ''et al.'' 2003'''<ref name=currieetal2003/></center></u> {{clade| style=font-size:80%;line-height:80% |label1=[[Tyrannosauridae]]&nbsp; |1={{clade |label1=<font color="white">void</font> |1=Albertosaurinae |label2=&nbsp;Tyrannosaurinae&nbsp; |2={{clade |label1=<font color="white">void</font> |1={{clade |label1=<font color="white">void</font> |1='''''Daspletosaurus''''' |2={{clade |label1=&nbsp;<font color="white">void</font>&nbsp; |1='''''[[Tarbosaurus]]''''' |2=''[[Alioramus]]''}} }} |2={{clade |label1=<font color="white">void</font> |1=''[[Nanotyrannus]]'' |2=''[[Tyrannosaurus]]'' }} }} }} }} {{userboxbottom}} ''Daspletosaurus'' belongs in the subfamily Tyrannosaurinae within the [[Family (biology)|family]] [[Tyrannosauridae]], along with ''[[Tarbosaurus]]'', ''Tyrannosaurus'' and possibly ''[[Alioramus]]''. Animals in this subfamily are more closely related to ''Tyrannosaurus'' than to ''[[Albertosaurus]]'' and are known for their robust build with proportionally larger skulls and longer [[femur|femora]] than in the other subfamily, the Albertosaurinae.<ref name=holtz2004/><ref name=currieetal2003>{{cite_journal |last=Currie |first=Philip J. |coauthors=Hurum, Jørn H; & Sabath, Karol. |authorlink=Phil Currie |year=2003 |title=Skull structure and evolution in tyrannosaurid phylogeny |journal=Acta Palaeontologica Polonica | volume=48 |issue=2 |pages=227–234 |url=http://app.pan.pl/acta48/app48-227.pdf|format=PDF}}</ref> ''Daspletosaurus'' is usually considered to be closely related to ''Tyrannosaurus rex'', or even a direct ancestor through [[anagenesis]].<ref name=horneretal1992>{{cite_journal |last=Horner |first=John R. |authorlink=Jack Horner (paleontologist) |coauthors=Varricchio, David J.; & Goodwin, Mark B. |year=1992 |title=Marine transgressions and the evolution of Cretaceous dinosaurs |journal=Nature |volume=358 |pages=59–61 |doi=10.1038/358059a0}}</ref> [[Gregory Paul]] reassigned ''D. torosus'' to the genus ''Tyrannosaurus'', creating the new combination ''Tyrannosaurus torosus'',<ref name=paul1988/> but this has not been generally accepted.<ref name=carr1999/><ref name=holtz2004/> Many researchers believe ''Tarbosaurus'' and ''Tyrannosaurus'' to be [[sister taxa]] or even to be the same genus, with ''Daspletosaurus'' a more [[Basal (phylogenetics)|basal]] relative.<ref name=holtz2004/><ref name=carretal2005>{{cite_journal |last=Carr |first=Thomas D. |coauthors=Williamson, Thomas E.; & Schwimmer, David R. |year=2005 |title=A new genus and species of tyrannosauroid from the Late Cretaceous (middle Campanian) Demopolis Formation of Alabama |journal=Journal of Vertebrate Paleontology |volume=25 |issue=1 |pages=119–143 |url=http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1671%2F0272-4634(2005)025%5B0119%3AANGASO%5D2.0.CO%3B2 |doi=10.1671/0272-4634(2005)025[0119:ANGASO]2.0.CO;2}}</ref> On the other hand, [[Phil Currie]] and colleagues find ''Daspletosaurus'' to be more closely related to ''Tarbosaurus'' and other [[Asia]]n tyrannosaurids like ''Alioramus'' than to the North American ''Tyrannosaurus''.<ref name=currieetal2003/> The [[systematics]] ([[evolution]]ary relationships) of ''Daspletosaurus'' may become clearer once all the species have been described. ==Discovery and naming== The [[type specimen]] of ''Daspletosaurus torosus'' ([[Canadian Museum of Nature|CMN]] 8506) is a partial skeleton including the skull, the shoulder, a forelimb, the [[pelvis]], a femur and all of the [[vertebra]]e from the neck, torso and hip, as well as the first eleven tail vertebrae. It was discovered in 1921 by [[Charles Mortram Sternberg]], who thought it was a new species of ''Gorgosaurus''. It was not until 1970 that the specimen was fully described by [[Dale Russell]], who made it the type of a new genus, ''Daspletosaurus'', from the [[Ancient Greek|Greek]] stems ''δασπλητo-/daspleto-'' ('frightful') and ''σαυρος/sauros'' ('lizard').<ref name=liddellscott>{{cite book |last=Liddell |first=Henry G. |authorlink=Henry Liddell |coauthors=& [[Robert Scott (philologist)|Scott, Robert]] |year=1980 |title=Greek-English Lexicon |edition=Abridged Edition |publisher=Oxford University Press, |location=Oxford |isbn=0-19-910207-4}}</ref> The [[type species]] is ''D. torosus'', which is [[Latin]] for 'muscular' or 'brawny.'<ref name=russell1970/> Aside from the type, there is only one other well-known specimen, a complete skeleton discovered in 2001. Both specimens were recovered from the [[Oldman Formation|Oldman]] [[geologic formation|Formation]] in the [[Judith River Group]] of Alberta. A specimen from the younger [[Horseshoe Canyon Formation]] in Alberta has been reassigned to ''Albertosaurus sarcophagus''.<ref name=currie2003a/> The Oldman Formation was deposited during the middle [[Campanian]] [[faunal stage|stage]] of the [[Late Cretaceous]], from about 77 to 76 [[Mega-annum|Ma]] (million years ago).<ref name=eberthhamblin1993>{{cite_journal |last=Eberth |first=David A. |coauthors=& Hamblin, Anthony P. |year=1993 |title=Tectonic, stratigraphic, and sedimentologic significance of a regional discontinuity in the Upper Judith River Group (Belly River wedge) of southern Alberta, Saskatchewan, and northern Montana |journal=Canadian Journal of Earth Sciences |volume=30 |pages=174–200}}</ref> ===Unnamed species=== [[Image:Daspleto steveoc.jpg|thumb|220px|right|Illustration of ''Daspletosaurus''.]] Two or three additional species have been assigned to the genus ''Daspletosaurus'' over the years, although as of 2007 none of these species have received a proper description or [[binomial nomenclature|scientific name]]. In the meantime, all are assigned to ''Daspletosaurus'' sp. although this does not imply that they all are the same species.<ref name=currie2003a/><ref name=holtz2004/> Along with the [[holotype]], Russell designated a specimen collected by [[Barnum Brown]] in 1913 as the [[paratype]] of ''D. torosus''. This specimen ([[American Museum of Natural History|AMNH]] 5438) consists of parts of the hindleg, the pelvis and some of its associated vertebrae. It was discovered in the upper part of the Oldman Formation in Alberta.<ref name=currie2003a/> This upper section has since been renamed the [[Dinosaur Park Formation]], which dates back to the middle Campanian, from 76–74 Ma (million years ago).<ref name=eberthhamblin1993/> In 1914, Brown collected a nearly complete skeleton and skull; forty years later his [[American Museum of Natural History]] sold this specimen to the [[Field Museum of Natural History]] in [[Chicago]]. It was mounted for display in Chicago and labeled as ''Albertosaurus libratus'' for many years, but after several skull features were later found to be modeled in plaster, including most of the teeth, the specimen ([[Field Museum of Natural History|FMNH]] PR308) was reassigned to ''Daspletosaurus''.<ref name=carr1999/> A total of eight specimens have been collected from the Dinosaur Park Formation over the years since, most of them within the boundaries of [[Dinosaur Provincial Park]]. Phil Currie believes that the Dinosaur Park specimens represent a new species of ''Daspletosaurus'', distinguished by certain features of the skull. Pictures of this new species have been published, but it still awaits a name and full description in print.<ref name=currie2003a/> A new tyrannosaur specimen ([[Sam Noble Oklahoma Museum of Natural History|OMNH]] 10131), including skull fragments, ribs and parts of the hindlimb, was reported from New Mexico in 1990 and assigned to the now-defunct genus ''[[Aublysodon]]''.<ref name=lehmancarpenter1990>{{cite_journal |last=Lehman |first=Thomas M. |coauthors=& [[Kenneth Carpenter|Carpenter, Kenneth]] |year=1990 |title=A partial skeleton of the tyrannosaurid dinosaur ''Aublysodon'' from the Upper Cretaceous of New Mexico |journal=Journal of Paleontology |volume=64 |issue=6 |pages=1026–1032 |url=http://links.jstor.org/sici?sici=0022-3360%28199011%2964%3A6%3C1026%3AAPSOTT%3E2.0.CO%3B2-D#abstract}}</ref> Many later authors have reassigned this specimen, along with a few others from New Mexico, to yet another unnamed species of ''Daspletosaurus''.<ref name=currie2003a/><ref name=holtz2004/><ref name=carrwilliamson2000>{{cite_book |last=Carr |first=Thomas D. |coauthors=& Williamson, Thomas E. |year=2000 |chapter=A review of Tyrannosauridae (Dinosauria: Coelurosauria) from New Mexico |editor=[[Spencer G. Lucas|Lucas, Spencer G.]]; & Heckert, Andrew B. (eds.). |title=Dinosaurs of New Mexico |series=''New Mexico Museum of Natural History and Science Bulletin'' '''17''' |pages=113-146}}</ref> However, recent unpublished research has suggested that this species, from the Hunter Wash Member of the [[Kirtland Formation]], is actually an early tyrannosaurid, perhaps related to ''[[Appalachiosaurus]]''.<ref name=mortimerdml>{{cite web |last=Mortimer |first=Michael |date=[[2002-10-16]] |url=http://dml.cmnh.org/2002Oct/msg00326.html |publisher=Dinosaur Mailing List |title=Details on SVP 2002 Part 2 |accessdate=2007-06-18}}</ref> There is currently disagreement over the age of the Kirtland Formation, with some workers claiming a late Campanian age,<ref name=sullivanlucas2006>{{cite_book |last=Sullivan |first=Robert M. |coauthors=& [[Spencer G. Lucas|Lucas, Spencer G.]] |year=2006 |chapter=The Kirtlandian land-vertebrate "age" - faunal composition, temporal position and biostratigraphic correlation in the nonmarine Upper Cretaceous of North America |editor=[[Spencer G. Lucas|Lucas, Spencer G.]]; & Sullivan, Robert M. (eds.). |title=Late Cretaceous vertebrates from the Western Interior |series=''New Mexico Museum of Natural History and Science Bulletin'' '''35''' |pages=7-29}}</ref> while others suggest a younger age in the early [[Maastrichtian]] stage.<ref name=ryan1997>{{cite_book |last=Ryan |first=Michael J. |year=1997 |chapter=Kirtland Formation |editor=[[Phil Currie|Currie, Philip J.]] & Padian, Kevin (eds.). |title=Encyclopedia of Dinosaurs |publisher=Academic Press |location=San Diego |pages=390-391 |isbn=0-12-226810-5}}</ref> In 1992, [[Jack Horner (paleontologist)|Jack Horner]] and colleagues published an extremely preliminary report of a tyrannosaurid from the upper parts of the Campanian [[Two Medicine Formation]] in Montana, which was interpreted as a transitional species between ''Daspletosaurus'' and the later ''Tyrannosaurus''.<ref name=horneretal1992/> Another partial skeleton was reported from the Upper Two Medicine in 2001, preserving the remains of a juvenile hadrosaur in its [[abdominal cavity]]. This specimen was assigned to ''Daspletosaurus'' but not to any particular species.<ref name=varricchio2001>{{cite_journal |last=Varricchio |first=David J. |year=2001 |title=Gut contents from a Cretaceous tyrannosaurid: implications for theropod dinosaur digestive tracts |journal=Journal of Paleontology |volume=75 |issue=2 |pages=401–406 |doi=10.1666/0022-3360(2001)075<0401:GCFACT>2.0.CO;2}} [[DOI]]: [http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1666%2F0022-3360(2001)075%3C0401%3AGCFACT%3E2.0.CO%3B2 10.1666/0022-3360(2001)075<0401:GCFACT>2.0.CO;2]</ref> The remains of at least three more ''Daspletosaurus'' have also been described in a Two Medicine [[bonebed]].<ref name=currieetal2005>{{cite_book |last=Currie |first=Philip J. |authorlink=Phil Currie |coauthors=Trexler, David; [[Eva Koppelhus|Koppelhus, Eva B.]]; Wicks, Kelly; & Murphy, Nate. |year=2005 |chapter=An unusual multi-individual tyrannosaurid bonebed in the Two Medicine Formation (Late Cretaceous, Campanian) of Montana (USA) |editor=[[Kenneth Carpenter|Carpenter, Kenneth]] (ed.). |title=The Carnivorous Dinosaurs |publisher=Indiana University Press |location=Bloomington |pages=313–324 |isbn=978-0253345394}}</ref> These specimens have not been described in detail, but Currie believes all of the Two Medicine material represents an as-yet-unnamed third species of ''Daspletosaurus''.<ref name=currie2003a/> ==Paleobiology== ===Coexistence with ''Gorgosaurus=== In the late Campanian of North America, ''Daspletosaurus'' was a contemporary of the albertosaurine tyrannosaurid ''Gorgosaurus''. This is one of the few examples of two tyrannosaur genera coexisting. In modern predator [[Guild (ecology)|guilds]], similarly-sized predators are separated into different [[ecological niche]]s by anatomical, behavioral or geographical differences that limit competition.<ref name=farlowpianka2002>{{cite_journal |last=Farlow |first=James O. |authorlink=James Farlow |coauthors=& Pianka, Eric R. |year=2002 |title=Body size overlap, habitat partitioning and living space requirements of terrestrial vertebrate predators: implications for the paleoecology of large theropod dinosaurs |journal=Historical Biology |volume=16 |issue=1 |pages=21–40 |doi=10.1080/0891296031000154687}} </ref> Several studies have attempted to explain niche differentiation in ''Daspletosaurus'' and ''Gorgosaurus''. Dale Russell hypothesized that the more lightly built and more common ''Gorgosaurus'' may have preyed on the abundant hadrosaurs of the time, while the more robust and less common ''Daspletosaurus'' may have specialized on the less prevalent but better-defended ceratopsids, which may have been more difficult to hunt.<ref name=russell1970/> However, a specimen of ''Daspletosaurus'' ([[Old Trail Museum|OTM]] 200) from the Two Medicine Formation preserves the digested remains of a juvenile hadrosaur in its gut region.<ref name=varricchio2001/> The higher and broader muzzles of tyrannosaurines like ''Daspletosaurus'' are mechanically stronger than the lower snouts of albertosaurines like ''Gorgosaurus'', although tooth strengths are similar between the two groups. This may indicate a difference in feeding mechanics or diet.<ref name=snivelyetal2006>{{cite_journal |last=Snively |first=Eric |coauthors=Henderson, Donald M.; & Phillips, Doug S. |year=2006 |title=Fused and vaulted nasals of tyrannosaurid dinosaurs: implications for cranial strength and feeding mechanics |journal=Acta Palaeontologica Polonica |volume=51 |issue=3 |pages=435–454 |url=http://app.pan.pl/acta51/app51-435.pdf|format=PDF}}</ref> Other authors have suggested that competition was limited by geographical separation. Unlike some other groups of dinosaurs, there appears to be no correlation with distance from the sea. Neither ''Daspletosaurus'' nor ''Gorgosaurus'' was more common at higher or lower elevations than the other.<ref name=farlowpianka2002/> However, while there is some overlap, ''Gorgosaurus'' appears to be more common at northern latitudes, with species of ''Daspletosaurus'' more abundant to the south. The same pattern is seen in other groups of dinosaurs. Chasmosaurine ceratopsians and hadrosaurine hadrosaurs are also more common in the Two Medicine Formation and in southwestern North America during the Campanian. [[Thomas R. Holtz, Jr.|Thomas Holtz]] has suggested that this pattern indicates shared ecological preferences between tyrannosaurines, chasmosaurines and hadrosaurines. Holtz notes that, at the end of the later [[Maastrichtian]] stage, tyrannosaurines like ''Tyrannosaurus rex'', hadrosaurines and chasmosaurines like ''[[Triceratops]]'' were widespread throughout western North America, while albertosaurines and centrosaurines went extinct, and lambeosaurines were very rare.<ref name=holtz2004/> ===Social behavior=== [[Image:Albertosaurus skull.jpg|thumb|''Daspletosaurus'' skull, Royal Tyrrell Museum]] A young specimen of the Dinosaur Park ''Daspletosaurus'' species ([[Royal Tyrrell Museum of Palaeontology|TMP]] 94.143.1) shows bite marks on the face that were inflicted by another tyrannosaur. The bite marks are healed over, indicating that the animal survived the bite. A full-grown Dinosaur Park ''Daspletosaurus'' (TMP 85.62.1) also exhibits tyrannosaur bite marks, showing that attacks to the face were not limited to younger animals. While it is possible that the bites were attributable to other species, intraspecific aggression, including facial biting, is very common among predators. Facial bites are seen in other tyrannosaurs like ''Gorgosaurus'' and ''Tyrannosaurus'', as well as in other theropod genera like ''[[Sinraptor]]'' and ''[[Saurornitholestes]]''. [[Darren Tanke]] and Phil Currie hypothesize that the bites are due to [[intraspecific competition]] for territory or resources, or for dominance within a social group.<ref name=tankecurrie1998>{{cite_journal |last=Tanke |first=Darren H. |coauthors=& [[Phil Currie|Currie, Philip J.]] |year=1998 |title=Head-biting behavior in theropod dinosaurs: paleopathological evidence |journal=Gaia |volume=15 |pages=167–184 |url=http://www.mnhn.ul.pt/geologia/gaia/12.pdf|format=PDF}} [not printed until 2000]</ref> Evidence that ''Daspletosaurus'' lived in social groups comes from a bonebed found in the Two Medicine Formation of Montana. The bonebed includes the remains of three ''Daspletosaurus'', including a large adult, a small juvenile, and another individual of intermediate size. At least five hadrosaurs are preserved at the same location. Geologic evidence indicates that the remains were not brought together by [[Current (fluid)|river currents]] but that all of the animals were buried simultaneously at the same location. The hadrosaur remains are scattered and bear numerous marks from tyrannosaur teeth, indicating that the ''Daspletosaurus'' were feeding on the hadrosaurs at the time of death. The cause of death is unknown. Currie speculates that the daspletosaurs formed a [[pack hunter|pack]], although this cannot be stated with certainty.<ref name=currieetal2005/> Other scientists are skeptical of the evidence for social groups in ''Daspletosaurus'' and other large theropods;<ref name=eberthmccrea2001>{{cite_journal |last=Eberth |first=David A. |coauthors=& McCrea, Richard T. |year=2001 |title=Were large theropods gregarious? |journal=Journal of Vertebrate Paleontology |volume=21 |issue=(Supplement to 3 - Abstracts of Papers, 61st Annual Meeting of the Society of Vertebrate Paleontology) |pages=46A}}[published abstract only]</ref> Brian Roach and Daniel Brinkman have suggested that ''Daspletosaurus'' social interaction would have more closely resembled the modern [[Komodo dragon]], where non-cooperative individuals mob carcasses, frequently attacking and even [[cannibalism (zoology)|cannibalizing]] each other in the process.<ref name=BRDB07>{{cite journal|last=Roach|first=Brian T.|coauthors=& Brinkman, Daniel L.|year=2007|title=A reevaluation of cooperative pack hunting and gregariousness in ''Deinonychus antirrhopus'' and other nonavian theropod dinosaurs|journal=Bulletin of the Peabody Museum of Natural History|volume=48|issue=1|pages=103–138|url=http://web.archive.org/web/20070810172000/http://www.peabody.yale.edu/scipubs/abstracts/abs_b48-1b.html|doi=10.3374/0079-032X(2007)48[103:AROCPH]2.0.CO;2|}}</ref> ===Life history=== [[Image:Tyrantgraph.png|thumb|380px|right|A graph showing the hypothesized growth curves (body mass versus age) of four tyrannosaurids. ''Daspletosaurus'' is shown in green. Based on Erickson ''et al''. 2004.]] Paleontologist [[Gregory Erickson (paleontologist)|Gregory Erickson]] and colleagues have studied the growth and life history of tyrannosaurids. Analysis of bone [[histology]] can determine the age of a specimen when it died. Growth rates can be examined when the age of various individuals are plotted against their size on a graph. Erickson has shown that after a long time as juveniles, tyrannosaurs underwent tremendous growth spurts for about four years midway through their lives. After the rapid growth phase ended with [[sexual maturity]], growth slowed down considerably in adult animals. Erickson only examined ''Daspletosaurus'' from the Dinosaur Park Formation, but these specimens show the same pattern. Compared to albertosaurines, ''Daspletosaurus'' showed a faster growth rate during the rapid growth period due to its higher adult weight. The maximum growth rate in ''Daspletosaurus'' was 180&nbsp;kilograms (400&nbsp;[[pound (mass)|lb]]) per year, based on a mass estimate of 1800&nbsp;kilograms (2&nbsp;tons) in adults. Other authors have suggested higher adult weights for ''Daspletosaurus''; this would change the magnitude of the growth rate but not the overall pattern.<ref name=ericksonetal2004/> By tabulating the number of specimens of each age group, Erickson and his colleagues were able to draw conclusions about life history in a population of ''Albertosaurus''. Their analysis showed that while juveniles were rare in the fossil record, subadults in the rapid growth phase and adults were far more common. While this could be due to preservation or collection [[Biased sample|biases]], Erickson hypothesized that the difference was due to low mortality among juveniles over a certain size, which is also seen in some modern large mammals like [[elephant]]s. This low mortality may have resulted from a lack of predation, since tyrannosaurs surpassed all contemporaneous predators in size by the age of two. Paleontologists have not found enough ''Daspletosaurus'' remains for a similar analysis, but Erickson notes that the same general trend seems to apply.<ref name=ericksonetal2006>{{cite_journal |last=Erickson |first=Gregory M. |coauthors= [[Phil Currie|Currie, Philip. J.]]; Inouye, Brian D.; & Wynn, Alice A. |year=2006 |title=Tyrannosaur life tables: an example of nonavian dinosaur population biology |journal=Science |volume=313 |pages=213–217 |doi=10.1126/science.1125721 |pmid=16840697}}</ref> ==Paleoecology== All known ''Daspletosaurus'' fossils have been found in formations dating to the middle to late Campanian stage of the Late Cretaceous Period, between 80 and 73 million years ago. Since the middle of the Cretaceous, North America had been divided in half by the [[Western Interior Seaway]], with much of Montana and Alberta below the surface. However, the uplift of the [[Rocky Mountains]] in the [[Laramide Orogeny]] to the west, which began during the time of ''Daspletosaurus'', forced the seaway to retreat eastwards and southwards. Rivers flowed down from the mountains and drained into the seaway, carrying sediment along with them that formed the Two Medicine Formation, the Judith River Group, and other [[sedimentary rock|sedimentary]] formations in the region. About 73 million years ago, the seaway began to advance westwards and northwards again, and the entire region was covered by the Bearpaw Sea, represented throughout the western United States and Canada by the massive [[Bearpaw Shale]].<ref name=englishjohnston2004>{{cite_journal |last=English |first=Joseph M. |coauthors=& Johnston, Stephen T. |year=2004 |title=The Laramide Orogeny: what were the driving forces? |journal=International Geology Review |volume=46 |issue=9 |pages=833–838 |url=http://www.ingentaconnect.com/content/bell/igr/2004/00000046/00000009/art00004 |doi=10.2747/0020-6814.46.9.833}}</ref><ref name=eberth1997>{{cite_book |last=Eberth |first=David A. |year=1997 |chapter=Judith River Wedge |editor=[[Phil Currie|Currie, Philip J.]] & Padian, Kevin (eds.). |title=Encyclopedia of Dinosaurs |publisher= Academic Press |location=San Diego |pages=199-204 |isbn=0-12-226810-5}}</ref><ref name=rogers1997>{{cite_book |last=Rogers |first=Raymond R. |year=1997 |chapter=Two Medicine Formation |editor=[[Phil Currie|Currie, Philip J.]] & Padian, Kevin (eds.). |title=Encyclopedia of Dinosaurs |publisher= Academic Press |location=San Diego |pages=199-204 |isbn=0-12-226810-5}}</ref> [[Image:Two Medicine.jpg|thumb|left|Exposures of the [[Two Medicine Formation]] in [[Montana]].]] ''Daspletosaurus'' lived in a vast floodplain along the western shore of the interior seaway. Large rivers watered the land, occasionally flooding and blanketing the region with new sediment. When water was plentiful, the region could support a great deal of plant and animal life, but periodic droughts also struck the region, resulting in mass mortality as preserved in the many bonebed deposits found in Two Medicine and Judith River sediments, including the ''Daspletosaurus'' bonebed.<ref name=rogers1990>{{cite_journal |last=Rogers |first=Raymond R. |year=1990 |title=Taphonomy of three dinosaur bonebeds in the Upper Cretaceous Two Medicine Formation of northwestern Montana: evidence for drought-induced mortality |journal=Palaios |volume=5 |issue=5 |pages=394–413 |doi=10.2307/3514834}}</ref> Similar conditions exist today in [[East Africa]].<ref name=falconlang2003>{{cite_journal |last=Falcon-Lang |first=Howard J. |year=2003 |title=Growth interruptions in silicified conifer woods from the Upper Cretaceous Two Medicine Formation, Montana, USA: implications for palaeoclimate and dinosaur palaeoecology |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=199 |pages=299–314 |doi=10.1016/S0031-0182(03)00539-X}}</ref> [[Volcanic eruption]]s from the west periodically blanketed the region with ash, also resulting in large-scale mortality, while simultaneously enriching the soil for future plant growth. It is these ash beds that allow precise [[radiometric dating]] as well. Fluctuating sea levels also resulted in a variety of other environments at different times and places within the Judith River Group, including offshore and nearshore marine habitats, coastal wetlands, deltas and lagoons, in addition to the inland floodplains.<ref name=eberth1997/> The Two Medicine Formation was deposited at higher elevations farther inland than the other two formations.<ref name=rogers1997/> The excellent [[vertebrate]] fossil record of Two Medicine and Judith River rocks resulted from a combination of abundant animal life, periodic natural disasters, and the deposition of large amounts of sediment. Many types of freshwater and [[estuarine]] [[fish]] are represented, including [[shark]]s, [[Batoidea|rays]], [[sturgeon]]s, [[gar]]s and others. The Judith River Group preserves the remains of many aquatic [[amphibian]]s and [[reptiles]], including [[frog]]s, [[salamander]]s, [[turtle]]s, ''[[Champsosaurus]]'' and [[crocodilia]]ns. Terrestrial lizards, including [[Teiidae|whiptail]]s, [[skink]]s, [[varanid|monitors]] and [[Anguidae|alligator lizards]] have also been discovered. [[Azhdarchid]] [[pterosaur]]s, and [[neornithes|neornithean birds]] like ''[[Apatornis]]'' flew overhead, while the [[Enantiornithes|enantiornithiform bird]] ''[[Avisaurus]]'' and several varieties of [[multituberculate]], [[marsupial]] and [[placental]] [[mammal]]s scurried beneath the feet of ''Daspletosaurus'' and other dinosaurs.<ref name=eberth1997/> In the Oldman Formation, ''Daspletosaurus torosus'' could have preyed upon hadrosaurs like ''[[Brachylophosaurus]]'' and ''[[Hypacrosaurus]]'', small [[ornithopod]]s like ''[[Orodromeus]]'', ceratopsians like ''[[Centrosaurus]]'', [[pachycephalosaur]]s, [[ornithomimid]]s, [[therizinosaur]]s and possibly [[ankylosaur]]s. Other predators included [[troodont]]s, [[oviraptorosaur]]s, the [[dromaeosaur]] ''[[Saurornitholestes]]'' and possibly an albertosaurine tyrannosaur (genus currently unknown). The Dinosaur Park and Two Medicine Formations have [[fauna]]s comparable to the Oldman, with the Dinosaur Park in particular preserving an unrivaled array of dinosaurs.<ref name=eberth1997/> The albertosaurine ''Gorgosaurus'' lived alongside species of ''Daspletosaurus'' in the Dinosaur Park and Upper Two Medicine environments.<ref name=farlowpianka2002/> Young tyrannosaurs may have filled the niches in between adult tyrannosaurs and smaller theropods, which were separated by two orders of magnitude in mass.<ref name=russell1970/><ref name=holtz2004/><ref name=snivelyetal2006/><ref name=farlow1976>{{cite_journal |last=Farlow |first=James O. |authorlink=James Farlow |year=1976 |title=Speculations about the diet and foraging behavior of large carnivorous dinosaurs |journal=American Midland Naturalist |volume=95 |issue=1 |pages=186–191 |url=http://links.jstor.org/sici?sici=0003-0031%28197601%2995%3A1%3C186%3ASATDAF%3E2.0.CO%3B2-5 |doi=10.2307/2424244}}</ref> ==References== {{reflist|2}} ==External links== {{Wikispecies|Daspletosaurus}} {{portalpar|Dinosaurs}} *[http://web.archive.org/web/20070125140546/staff.washington.edu/eoraptor/Tyrannosauroidea.html#Daspletosaurustorosus Discussion and specimen list] at The Theropod Database. *[http://web.archive.org/web/20070109160125/http://www.paleograveyard.com/daspletosaurus.html Skull image] of the [[Dinosaur Park Formation]] ''Daspletosaurus'' at The Graveyard. {{featured article}} [[Category:Cretaceous dinosaurs]] [[Category:Dinosaurs of North America]] [[Category:Tyrannosaurs]] [[cs:Daspletosaurus]] [[de:Daspletosaurus]] [[es:Daspletosaurus]] [[eo:Daspletosaŭro]] [[fr:Dasplétosaure]] [[it:Daspletosaurus torosus]] [[lv:Daspletozaurs]] [[nl:Daspletosaurus]] [[ja:ダスプレトサウルス]] [[pl:Daspletozaur]] [[pt:Daspletossauro]] [[simple:Daspletosaurus]] [[sk:Daspletosaurus]] [[fi:Daspletosaurus]] [[sv:Daspletosaurus]] [[vo:Daspletosaurus]] [[zh:惧龙]]