Tarbosaurus
195481
225634683
2008-07-14T17:39:11Z
216.77.224.6
{{Taxobox
| name = ''Tarbosaurus''
| fossil_range = [[Late Cretaceous]]
| image = Tarbosaurus080eue.jpg
| image_width = 200px
| image_caption = A ''Tarbosaurus'' skull
| regnum = [[Animal]]ia
| phylum = [[Chordate|Chordata]]
| classis = [[Reptile|Sauropsida]]
| superordo = [[Dinosaur]]ia
| ordo = [[Saurischia]]
| subordo = [[Theropod]]a
| familia = [[Tyrannosaurid]]ae
| genus = '''''Tarbosaurus'''''
| genus_authority = [[Evgeny Maleev|Maleev]], 1955
| subdivision_ranks = [[Species]]
| subdivision =
*'''''T. bataar''''' <small>Maleev, 1955 ([[Type (zoology)|type]])</small>
| synonyms =
* ''Maleevosaurus'' <small>[[Kenneth Carpenter|Carpenter]], 1992</small>
* ''Jenghizkhan'' <small>[[George Olshevsky|Olshevsky]], 1995</small>
* ''[[Chingkankousaurus]]''? <small>[[Yang Zhongjian|Young]], 1958</small>
* ''Shanshanosaurus''? <small>[[Dong Zhiming|Dong]], 1977</small>
}}
'''''Tarbosaurus''''' ({{pronEng|ˌtɑrboʊˈsɔrəs}} or TAHR-bow-''SAWR''-us; meaning "terrifying lizard") is a [[genus]] of [[tyrannosaurid]] [[theropod]] [[dinosaur]] that flourished in [[Asia]] between 70 and 65 [[million years ago]], near the end of the Late [[Cretaceous]] [[Period (geology)|Period]]. [[Fossil]]s have been recovered in [[Mongolia]] with more fragmentary remains found further afield in parts of [[China]]. Although many [[species]] have been named, modern paleontologists recognize only one, ''T. bataar'', as valid. Some experts contend that this species is actually an Asian representative of the [[North America]]n genus ''[[Tyrannosaurus]]''; if true, this would invalidate the genus ''Tarbosaurus'' altogether.
''Tarbosaurus'' and ''Tyrannosaurus'' are considered closely related genera, even if they are not [[synonym (taxonomy)|synonymous]]. ''[[Alioramus]]'', also from Mongolia, is thought by some authorities to be the closest relative of ''Tarbosaurus''. Like most known tyrannosaurids, ''Tarbosaurus'' was a large [[biped]]al [[predation|predator]], weighing more than a [[short ton|ton]] and equipped with dozens of large, sharp teeth. It had a unique locking mechanism in its lower jaw and the smallest forelimbs relative to body size of all tyrannosaurids, renowned for their disproportionately tiny, two-fingered forelimbs.
''Tarbosaurus'' lived in a humid [[floodplain]] criss-crossed by river channels. In this environment, it was an [[apex predator]] at the top of the [[food chain]], probably preying on other large dinosaurs like the [[hadrosaur]] ''[[Saurolophus]]'' or the [[sauropod]] ''[[Nemegtosaurus]]''. ''Tarbosaurus'' is very well-represented in the [[fossil]] record, known from dozens of specimens, including several complete skulls and skeletons. These remains have allowed scientific studies focusing on its [[phylogeny]], skull mechanics, and brain structure.
==Description==
[[Image:Tarbosaurusscale.png|left|thumb|''Tarbosaurus baatar'' with a human for scale]]
[[Image:TarbosaurusP1050352.jpg|left|thumb|''Tarbosaurus'' skeleton in University Geology and Palaeontology Museum, [[Münster]], [[Germany]]]]
Although smaller than ''Tyrannosaurus'', ''Tarbosaurus'' was one of the largest tyrannosaurids. The largest known individuals were between 10 and 12 [[meter]]s (33 to 40 [[Foot (length)|ft]]) long, each with a head held up to 5 meters (16.5 ft) above the ground.<ref name=maleev1955b>{{cite_journal |last=Maleev |first=Evgeny A. |authorlink=Evgeny Maleev |year=1955 |title=New carnivorous dinosaurs from the Upper Cretaceous of Mongolia. |journal=Doklady, Academy of Sciences USSR |volume=104 |issue=5 |pages=779–783 |language=Russian}}</ref> The mass of a fully grown individual has never been published, although it is considered comparable to or slightly smaller than ''Tyrannosaurus''.<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]]; and 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>
The largest known ''Tarbosaurus'' skull is more than 1.3 meters (4 ft) long, larger than all other tyrannosaurids except ''Tyrannosaurus''.<ref name=holtz2004/> The skull was tall, like that of ''Tyrannosaurus'', but not as wide, especially towards the rear. The unexpanded rear of the skull meant that ''Tarbosaurus'' eyes did not face directly forwards, suggesting that it lacked the [[binocular vision]] of ''Tyrannosaurus''. Large [[fenestra]]e (openings) in the skull reduced its weight. Between 60 and 64 teeth lined its jaws, slightly more than in ''Tyrannosaurus'' but fewer than in smaller tyrannosaurids like ''[[Gorgosaurus]]'' and ''Alioramus''. Most of its teeth were oval in [[Cross section (geometry)|cross section]], although the teeth of the [[premaxilla]] at the tip of the upper jaw had a ''D''-shaped cross section. This [[heterodonty]] is characteristic of the family. The longest teeth were in the [[maxilla]] (upper jaw bone), with [[tooth crown|crowns]] up to 85 [[millimeter]]s (3.3 [[inch|in]]) long. In the [[mandible|lower jaw]], a ridge on the outer surface of the [[angular]] bone articulated with the rear of the [[dentary]] bone, creating a locking mechanism unique to ''Tarbosaurus'' and ''Alioramus''. Other tyrannosaurids lacked this ridge and had more flexibility in the lower jaw.<ref name=hurumsabath2003>{{cite_journal |last=Hurum |first= Jørn H. |coauthors=and Sabath, Karol. |year=2003 |title=Giant theropod dinosaurs from Asia and North America: Skulls of ''Tarbosaurus bataar'' and ''Tyrannosaurus rex'' compared |journal=Acta Palaeontologica Polonica |volume=48 |issue=2 |pages=161–190 |format=PDF|url=http://www.app.pan.pl/acta48/app48-161.pdf}}</ref>
Tyrannosaurids varied little in body form, and ''Tarbosaurus'' was no exception. The head was supported by an ''S''-shaped neck, while the rest of the [[vertebral column]], including the long tail, was held horizontally. ''Tarbosaurus'' had tiny, two-fingered forelimbs, which were smaller relative to its body size than those of any other member of the family. In contrast, the three-toed hindlimbs were long and thick, supporting the body in a bipedal posture. The long, heavy tail served as a [[counterweight]] to the head and torso and placed the [[center of gravity]] over the hips.<ref name=maleev1955b/><ref name=holtz2004/>
==Classification and systematics==
{{userboxtop|align=right|bordercolor=lightgray|toptext=[[Cladistics#Cladograms|Cladograms]] of [[Tyrannosauridae]] highlighting the position of ''Tarbosaurus''}}
<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]]
|1={{clade
|label1=<font color="white">void</font>
|1=Albertosaurinae
|label2= Tyrannosaurinae
|2={{clade
|1={{clade
|label1=<font color="white">void</font>
|1=''[[Daspletosaurus]]''
|2={{clade
|label1= <font color="white">void</font>
|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]]
|1={{clade
|label1=<font color="white">void</font>
|1=Albertosaurinae
|label2= Tyrannosaurinae
|2={{clade
|label1=<font color="white">void</font>
|1={{clade
|label1=<font color="white">void</font>
|1=''[[Daspletosaurus]]''
|2={{clade
|label1= <font color="white">void</font>
|1='''''[[Tarbosaurus]]'''''
|2=''[[Alioramus]]''}} }}
|2={{clade
|label1=<font color="white">void</font>
|1=''[[Nanotyrannus]]''
|2=''[[Tyrannosaurus]]''
}} }} }} }}
{{userboxbottom}}
''Tarbosaurus'' is classified as a [[theropod]] in the subfamily Tyrannosaurinae within the family [[Tyrannosauridae]]. Other members include ''Tyrannosaurus'' and the earlier ''[[Daspletosaurus]]'', both from North America,<ref name=carretal2005>{{cite_journal |last=Carr |first=Thomas D. |coauthors=Williamson, Thomas E.; and 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&ct=1&SESSID=1e13f2ec2859222c63f32587a0f4c77b |doi=10.1671/0272-4634(2005)025[0119:ANGASO]2.0.CO;2}}</ref> and possibly the Mongolian genus ''Alioramus''.<ref name=hurumsabath2003/><ref name=currieetal2003>{{cite_journal |last=Currie |first=Philip J. |coauthors=Hurum, Jørn H; and 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 |format=PDF|url=http://app.pan.pl/acta48/app48-227.pdf}}</ref> 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]]s than in the other subfamily, the Albertosaurinae.<ref name=holtz2004/>
''Tarbosaurus bataar'' was originally described as a species of ''Tyrannosaurus'',<ref name=maleev1955a>{{cite_journal |last=Maleev |first=Evgeny A. |authorlink=Evgeny Maleev |year=1955 |title=Giant carnivorous dinosaurs of Mongolia |journal=Doklady, Academy of Sciences USSR |volume=104 |issue=4 |pages=634–637}}</ref> an arrangement that has been supported by more recent studies.<ref name=carretal2005/><ref name=carpenter1992>{{cite_book |last=Carpenter |first=Ken. |authorlink=Kenneth Carpenter |year=1992 |chapter=Tyrannosaurids (Dinosauria) of Asia and North America |editor=Mateer, Niall J.; and Chen Peiji (eds.) |title=Aspects of Nonmarine Cretaceous Geology |location=Beijing |publisher=China Ocean Press |pages=250–268 |url=https://scientists.dmns.org/sites/kencarpenter/PDFs%20of%20publications/pdfs.aspx}}</ref> Others prefer to keep the genera separate, while still recognizing them as [[sister taxa]].<ref name=holtz2004/> A 2003 [[cladistic]] analysis based on skull features instead identified ''Alioramus'' as the closest known relative of ''Tarbosaurus'', as the two genera share skull characteristics that are related to stress distribution and that are not found in other tyrannosaurines. If proven, this relationship would preclude ''Tarbosaurus'' from becoming a synonym for ''Tyrannosaurus'' and would suggest that separate tyrannosaurine lineages [[evolution|evolved]] in Asia and North America.<ref name=hurumsabath2003/><ref name=currieetal2003/> The single known specimen of ''Alioramus'', which shows juvenile characteristics, is not likely a juvenile ''Tarbosaurus'' because of its much higher tooth count (76 to 78 teeth) and the unique row of bony bumps along the top of its snout.<ref name=currie2003>{{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 |format=PDF|url=http://app.pan.pl/acta48/app48-191.pdf}}</ref>
==Discovery and naming==
In 1946, a joint [[USSR|Soviet]]-Mongolian expedition to the [[Gobi Desert]] in the Mongolian province of [[Ömnögovi]] turned up a large theropod skull and some [[vertebra]]e in the [[Nemegt Formation]]. In 1955, [[Evgeny Maleev]], a Russian [[paleontologist]], made this specimen the [[holotype]] ([[Paleontological Institute of Russian Academy of Sciences|PIN]] 551-1) of a new species, which he called ''Tyrannosaurus bataar''.<ref name=maleev1955a/> The species name is a misspelling of the Mongolian баатар/''baatar'' ("hero").<ref name=hurumsabath2003/> In the same year, Maleev also described and named three new theropod skulls, each associated with skeletal remains discovered by the same expedition in 1948 and 1949. The first of these (PIN 551-2) was named ''Tarbosaurus efremovi'', a new generic name composed of the [[Ancient Greek]] ''ταρβος''/''tarbos'' ("terror", "alarm", "awe", or "reverence") and ''σαυρος''/''sauros'' ("lizard")<ref name=liddellscott>{{cite book |last=Liddell |first=Henry G. |authorlink=Henry Liddell |coauthors=and [[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>, and the species named after [[Ivan Yefremov]], a Russian paleontologist and [[science fiction]] author. The other two (PIN 553-1 and PIN 552-2) were also named as new species and assigned to the North American genus ''Gorgosaurus'' (''G. lancinator'' and ''G. novojilovi'', respectively). All three of these latter specimens are smaller than the first.<ref name=maleev1955b/>
[[Image:Map mn umnugobi aimag.png|thumb|left|[[Ömnögovi]], the [[Mongolia]]n [[Aimags of Mongolia|aimag]] (province) where most ''Tarbosaurus'' remains have been discovered]]
A 1965 paper by [[Anatoly Konstantinovich Rozhdestvensky|A.K. Rozhdestvensky]] recognized all of Maleev's specimens as different [[ontogeny|growth stages]] of the same species, which he believed to be distinct from the North American ''Tyrannosaurus''. He created a new combination, ''Tarbosaurus bataar'', to include all the specimens described in 1955 as well as newer material.<ref name=rozhdestvensky1965>{{cite_journal |last=Rozhdestvensky |first=Anatoly K. |authorlink=Anatoly Konstantinovich Rozhdestvensky |year=1965 |title=Growth changes in Asian dinosaurs and some problems of their taxonomy |journal=Paleontological Journal |volume=3 |pages=95–109}}</ref> Later authors, including Maleev himself,<ref name=maleev1974>{{cite_journal |last=Maleev |first=Evgeny A. |authorlink=Evgeny Maleev |year=1974 |title=Gigantic carnosaurs of the family Tyrannosauridae |journal=The Joint Soviet-Mongolian Paleontological Expedition Transactions |volume=1 |pages=132–191}}</ref> agreed with Rozhdestvensky's analysis, although some used the name ''Tarbosaurus efremovi'' rather than ''T. bataar''.<ref name=barsbold1983>{{cite_journal |last=Barsbold |first=Rinchen. |authorlink=Rinchen Barsbold |year=1983 |title=Carnivorous dinosaurs from the Cretaceous of Mongolia |journal=The Joint Soviet-Mongolian Paleontological Expedition Transactions |volume=19 |pages=5–119}}</ref> American paleontologist [[Kenneth Carpenter]] re-examined the material in 1992. He concluded that it belonged to the genus ''Tyrannosaurus'', as originally published by Maleev, and lumped all the specimens into the species ''Tyrannosaurus bataar'' except the remains that Maleev had named ''Gorgosaurus novojilovi''. Carpenter thought this specimen represented a separate, smaller genus of tyrannosaurid, which he called ''Maleevosaurus novojilovi''.<ref name=carpenter1992/> [[George Olshevsky]] created the new generic name ''Jenghizkhan'' (after [[Genghis Khan]]) for ''Tyrannosaurus bataar'' in 1995, while also recognizing ''Tarbosaurus efremovi'' and ''Maleevosaurus novojilovi'', for a total of three distinct, contemporaneous genera from the Nemegt Formation.<ref name=olshevskyford1995>{{cite_journal |last=Olshevsky |first=George |authorlink=George Olshevsky |coauthors= and Ford, Tracy L. |year=1995 |title=The origin and evolution of the tyrannosaurids, part 1 |language=Japanese |journal=Dinosaur Frontline |volume=9 |pages=92–119}}</ref> A 1999 study subsequently reclassified ''Maleevosaurus'' as a juvenile ''Tarbosaurus''.<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 |url=http://www.vertpaleo.org/publications/jvp/19-497-520.cfm}}</ref> All research published since 1999 recognizes only a single species, which is either called ''Tarbosaurus bataar''<ref name=holtz2004/><ref name=currieetal2003/><ref name=xuetal2004>{{cite_journal |last= Xu Xing |authorlink=Xu Xing |coauthors= Norell, Mark A.; Kuang Xuewen; Wang Xiaolin;, Zhao Qi; and Jia Chengkai. |year=2004 |title=Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids |journal=Nature |volume=431 |issue=7009 |pages=680–684 |doi=10.1038/nature02855}}</ref> or ''Tyrannosaurus bataar''.<ref name=carretal2005/>
After the original Russian-Mongolian expeditions in the 1940s, [[Poland|Polish]]-Mongolian joint expeditions to the Gobi Desert began in 1963 and continued until 1971, recovering many new fossils, including new specimens of ''Tarbosaurus'' from the Nemegt Formation.<ref name=hurumsabath2003/> Expeditions involving [[Japan]]ese and Mongolian scientists between 1993 and 1998,<ref name=watabesuzuki2000>{{cite_journal |last=Watabe |first=Masato |coauthors=and Suzuki, Shigeru. |year=2000 |title=Cretaceous fossil localities and a list of fossils collected by the Hayashibara Museum of Natural Sciences and Mongolian Paleontological Center Joint Paleontological Expedition (JMJPE) from 1993 through 1998 |journal=Hayashibara Museum of Natural Sciences Research Bulletin |volume=1 |pages=99–108}}</ref> as well as private expeditions hosted by [[Canada|Canadian]] paleontologist [[Phil Currie]] around the turn of the 21st century, discovered and collected further ''Tarbosaurus'' material.<ref name=currie2001>{{cite_book |last=Currie |first=Philip J. |authorlink=Phil Currie |year=2001 |chapter=Nomadic Expeditions, Inc., report of fieldwork in Mongolia, September 2000. |title=Alberta Palaeontological Society, Fifth Annual Symposium, Abstract Volume. |publisher=Mount Royal College |location=Calgary |pages=12–16}}</ref><ref name=currie2002>{{cite_book |last=Currie |first=Philip J. |authorlink=Phil Currie |year=2002 |chapter=Report on fieldwork in Mongolia, September 2001. |title=Alberta Palaeontological Society, Sixth Annual Symposium, "Fossils 2002," Abstract Volume. |publisher=Mount Royal College |location=Calgary |pages=8–12}}</ref> More than 30 specimens are known, including more than 15 skulls and several complete postcranial skeletons.<ref name=holtz2004/>
===Possible synonyms===
[[China|Chinese]] paleontologists discovered a partial skull and skeleton of a small theropod ([[Institute of Vertebrate Paleontology and Paleoanthropology|IVPP]] V4878) in the [[Xinjiang]] Autonomous Region of China in the mid-1960s. In 1977, [[Dong Zhiming]] described this specimen, which was recovered from the [[Subashi Formation]], as a new genus and species, ''Shanshanosaurus huoyanshanensis''.<ref name=dong1977>{{cite_journal|last=Dong Zhiming.|authorlink=Dong Zhiming|year=1977|title=On the dinosaurian remains from Turpan, Xinjiang|journal=Vertebrata PalAsiatica|volume=15|pages=59–66|language=Chinese}}</ref> [[Gregory Paul]] recognized ''Shanshanosaurus'' as a tyrannosaurid in 1988, referring it to the now-defunct genus ''[[Aublysodon]]''.<ref name=paul1988>{{cite_book|last=Paul|first=Gregory S. |year=1988|title=Predatory Dinosaurs of the World|location=New York|publisher=Simon & Schuster |pages=464pp}}</ref> Dong and Currie later re-examined the specimen and deemed it to be a juvenile of a larger species of tyrannosaurid. These authors refrained from assigning it to any particular genus but suggested ''Tarbosaurus'' as a possibility.<ref name=curriedong2001>{{cite_journal |last=Currie |first=Philip J. |authorlink=Phil Currie |coauthors=and [[Dong Zhiming]]. |year=2001 |title=New information on ''Shanshanosaurus huoyanshanensis'', a juvenile tyrannosaurid (Theropoda, Dinosauria) from the Late Cretaceous of China|journal=Canadian Journal of Earth Sciences|volume=38|issue=12|pages=1729–1737|doi=10.1139/cjes-38-12-1729}}</ref> Over the years, other Chinese localities have produced tyrannosaurid teeth and fragmentary remains, several of which have been given names. ''Albertosaurus periculosis'', ''Tyrannosaurus luanchuanensis'', ''Tyrannosaurus turpanensis'' and ''[[Chingkankousaurus|Chingkankousaurus fragilis]]'' are often considered synonyms of ''Tarbosaurus''.<ref name=holtz2004/>
Named in 1976 by [[Sergei Kurzanov]], ''[[Alioramus]]'' is another genus of tyrannosaurid from slightly older sediments in Mongolia.<ref name=kurzanov1976>{{cite_journal|last=Kurzanov |first=Sergei M. |authorlink=Sergei Kurzanov |year=1976|title=A new Late Cretaceous carnosaur from Nogon−Tsav, Mongolia |language=Russian|journal=The Joint Soviet-Mongolian Paleontological Expedition Transactions |volume=3|pages=93–104}}</ref> Several analyses have concluded ''Alioramus'' was quite closely related to ''Tarbosaurus''.<ref name=hurumsabath2003/><ref name=currieetal2003/> It was described as an adult, but its long, low skull is characteristic of a juvenile tyrannosaurid. This led Currie to speculate that ''Alioramus'' might represent a juvenile ''Tarbosaurus'', but he noted that the much higher tooth count and row of crests on top of the snout suggested otherwise.<ref name=currie2003/>
==Paleobiology==
Like several other large tyrannosaurids, ''Tarbosaurus'' is known from relatively abundant and well-preserved fossil material. In fact, one quarter of all fossils collected from the Nemegt Formation belong to ''Tarbosaurus''.<ref name=jerzykiewiczrussell1991/> Although ''Tarbosaurus'' has not been studied as thoroughly as the North American tyrannosaurids,<ref name=hurumsabath2003/> the available material has allowed scientists to draw limited conclusions about its biology.
===Skull mechanics===
[[Image:Scan001tarb7.jpg|thumb|Mounted cast of a ''Tarbosaurus'' skeleton in the [[Copenhagen]] Experimentarium]]
The skull of ''Tarbosaurus'' was completely described for the first time in 2003. Scientists noted key differences between ''Tarbosaurus'' and the North American tyrannosaurids. Many of these differences are related to the handling of stress by the skull bones during a bite. When the upper jaw bit down on an object, [[force]] was transmitted up through the maxilla, the primary tooth-bearing bone of the upper jaw, into surrounding skull bones. In North American tyrannosaurids, this force went from the maxilla into the fused [[nasal bone]]s on top of the snout, which were firmly connected in the rear to the [[lacrimal bone]]s by bony struts. These struts locked the two bones together, suggesting that force was then transmitted from the nasals to the lacrimals.<ref name=hurumsabath2003/>
''Tarbosaurus'' lacked these bony struts, and the connection between the nasals and lacrimals was weak. Instead, a backwards projection of the maxilla was massively developed in ''Tarbosaurus'' and fit inside a sheath formed from the lacrimal. This projection was a thin, bony plate in North American tyrannosaurids. The large backwards projection suggests that force was transmitted more directly from the maxilla to the lacrimal in ''Tarbosaurus''. The lacrimal was also more firmly anchored to the [[frontal bone|frontal]] and [[prefrontal bone]]s in ''Tarbosaurus''. The well-developed connections between the maxilla, lacrimal, frontal and prefrontal would have made its entire upper jaw more rigid.<ref name=hurumsabath2003/>
Another major difference between ''Tarbosaurus'' and its North American relatives was its more rigid mandible (lower jaw). While many theropods, including North American tyrannosaurids, had some degree of flexibility between the bones in the rear of the mandible and the dentary in the front, ''Tarbosaurus'' had a locking mechanism formed from a ridge on the surface of the angular, which articulated with a square process on the rear of the dentary.<ref name=hurumsabath2003/>
Some scientists have [[hypothesis|hypothesized]] that the more rigid skull of ''Tarbosaurus'' was an adaptation to hunting the massive [[titanosaurid]] [[sauropod]]s found in the Nemegt Formation, which did not exist in most of North America during the Late Cretaceous. The differences in skull mechanics also have an impact on tyrannosaurid phylogeny. ''Tarbosaurus''-like articulations between the skull bones are also seen in ''Alioramus'' from Mongolia, suggesting that it, and not ''Tyrannosaurus'', is the closest relative of ''Tarbosaurus''. Similarities between ''Tarbosaurus'' and ''Tyrannosaurus'' might therefore be related to their large size, independently developed through [[convergent evolution]].<ref name=hurumsabath2003/>
===Brain structure===
[[Image:Tarbosaurus Bataar paris.JPG|thumb|left|Cast of a ''Tarbosaurus bataar'' skull]]
A ''Tarbosaurus'' skull found in 1948 by Soviet and Mongolian scientists (PIN 553-1, originally called ''Gorgosaurus lancinator'') included the skull cavity that held the brain. Making a plaster [[Casting|cast]], called an ''[[endocranial cast|endocast]]'', of the inside of this cavity allowed Maleev to make preliminary observations about the shape of a ''Tarbosaurus'' brain.<ref name=maleev1965>{{cite_journal |last=Maleev |first=Evgeny A. |authorlink=Evgeny Maleev |year=1965 |title=On the brain of carnivorous dinosaurs |language=Russian |journal=Paleontological Journal |volume=2 |pages=141–143}}</ref> A newer [[polyurethane]] rubber cast allowed a more detailed study of ''Tarbosaurus'' brain structure and function.<ref name=savelievalifanov2005>{{cite_journal |last=Saveliev |first=Sergei V. |coauthors=and Alifanov, Vladimir R. |year=2005 |title=A new study of the brain of the predatory dinosaur ''Tarbosaurus bataar'' (Theropoda, Tyrannosauridae) |journal=Paleontological Journal |volume=41 |issue=3 |pages=281–289 |doi=10.1134/S0031030107030070}}</ref>
''Tyrannosaurus rex'' brain structure has also been analyzed,<ref name=brochu2000>{{cite_journal |last=Brochu |first=Christopher A. |year=2000 |title=A digitally-rendered endocast for ''Tyrannosaurus rex'' |journal=Journal of Vertebrate Paleontology |volume=20 |issue=1 |pages=1–6 |url=http://www.bioone.org/perlserv/?request=get-toc&issn=0272-4634&volume=20&issue=1 |doi=10.1671/0272-4634(2000)020[0001:ADREFT]2.0.CO;2}}</ref> and ''Tarbosaurus'' was similar, differing only in the positions of some [[cranial nerve]] roots, including the [[trigeminal nerve|trigeminal]] and [[accessory nerve]]s. Tyrannosaurid brains were more similar to those of [[crocodilia]]ns and other [[reptile]]s than to [[bird]]s. The total brain volume for a 12 meter (40 foot) ''Tarbosaurus'' is estimated at only 184 [[cubic centimeters|centimeters<sup>3</sup>]] (11.2 [[Cubic inch|in<sup>3</sup>]]). The large size of the [[olfactory bulb]]s, as well as the [[terminal nerve|terminal]] and [[olfactory nerve]]s, suggest that ''Tarbosaurus'' had a keen [[sense of smell]], as was also the case with ''Tyrannosaurus''. The [[Olfactory_bulb#Accessory_olfactory_bulb|vomeronasal bulb]] is large and differentiated from the olfactory bulb, indicating a well-developed [[Jacobsen's organ]], which was used to detect [[pheromone]]s. This may imply that ''Tarbosaurus'' had complex mating behavior. The [[auditory nerve]] was also large, suggesting good [[Hearing (sense)|hearing]], which may have been useful for auditory [[animal communication|communication]] and spatial awareness. The nerve had a well-developed [[Vestibular system|vestibular]] component as well, which implies a good sense of balance and coordination. In contrast, the nerves and brain structures associated with [[eyesight]] were smaller and undeveloped. The [[midbrain tectum]], responsible for visual processing in reptiles, was very small in ''Tarbosaurus'', as were the [[optic nerve]] and the [[oculomotor nerve]], which controls eye movement. Unlike ''Tyrannosaurus'', which had forward-facing eyes that provided some degree of binocular vision, ''Tarbosaurus'' had a narrower skull more typical of other tyrannosaurids in which the eyes faced primarily sideways. All of this suggests that ''Tarbosaurus'' relied more on its senses of smell and hearing than on its eyesight.<ref name=savelievalifanov2005/>
==Paleoecology==
[[Image:TarbosaurusDB.jpg|thumb|Illustration of ''Tarbosaurus'']]
The vast majority of ''Tarbosaurus'' fossils are known from the [[Nemegt Formation]] of southern Mongolia. This [[geologic formation]] has never been [[radiometric dating|dated radiometrically]], but the [[fauna]] present in the fossil record indicate it was probably deposited during the [[Maastrichtian]] stage, at the end of the [[Late Cretaceous]].<ref name=jerzykiewiczrussell1991>{{cite_journal |last=Jerzykiewicz |first=Tomasz |coauthors=and [[Dale Russell|Russell, Dale A.]] |year=1991 |title=Late Mesozoic stratigraphy and vertebrates of the Gobi Basin |journal=Cretaceous Research |volume=12 |issue=4 |pages=345–377 |doi=10.1016/0195-6671(91)90015-5}}</ref> The Maastrichtian lasted from 70 to 65 million years ago.<ref name=gradsteinetal2005>{{cite_book |last=Gradstein |first=Felix M. |coauthors=Ogg, James G.; and Smith, Alan G. |year=2005 |title=A Geologic Time Scale 2004 |location=Cambridge |publisher=Cambridge University Press |pages=500pp. |isbn=978-0521781428}}</ref> The [[Subashi Formation]], in which ''Shanshanosaurus'' remains were discovered, is also Maastrichtian in age.<ref name=shenmateer1992>{{cite_book |last=Shen Y.B. |coauthors=and Mateer, Niall J. |year=1992 |chapter=An outline of the Cretaceous System in northern Xinjiang, western China |title=Aspects of Nonmarine Cretaceous Geology |editors=Mateer, Niall J.; and Chen Peiji (eds.) |location=Beijing |publisher=China Ocean Press |pages=49–77}}</ref>
Nemegt sediments preserve large river channels and soil deposits that indicate a far more humid climate than those suggested by the underlying [[Barun Goyot Formation|Barun Goyot]] and [[Djadochta Formation]]s. However, [[Caliche (mineral)|caliche]] deposits indicate at least periodic droughts. Sediment was deposited in the channels and floodplains of large rivers. Occasional [[mollusc]] fossils are found, as well as a variety of other aquatic animals like fish and turtles.<ref name=jerzykiewiczrussell1991/> Crocodilians included several species of ''[[Shamosuchus]]'', a genus with teeth adapted for crushing shells.<ref name=efimov1983>{{cite_journal |last=Efimov |first=Mikhail B. |year=1983 |title=Revision of the fossil crocodiles of Mongolia. |language=Russian |journal=The Joint Soviet-Mongolian Paleontological Expedition Transactions |volume=24 |pages=76–95}}</ref> [[Mammal]] fossils are exceedingly rare in the Nemegt Formation, but many birds are known, including the [[enantiornithine]] ''[[Gurilynia]]'' and the [[Hesperornithes|hesperornithiform]] ''[[Judinornis]]'', as well as ''[[Teviornis]]'', an early representative of the still-existing [[Anseriformes]] (waterfowl), a [[Bird#Modern_bird_orders|bird order]]. Scientists have described many dinosaurs from the Nemegt, including [[ankylosaurid]]s such as ''[[Tarchia]]'' and [[pachycephalosaur]]s such as ''[[Homalocephale]]'' and ''[[Prenocephale]]''.<ref name=jerzykiewiczrussell1991/> By far the largest predator of the time, adult ''Tarbosaurus'' most likely preyed upon large hadrosaurs such as ''Saurolophus'' and ''[[Barsboldia]]'' or sauropods such as ''Nemegtosaurus'' and ''[[Opisthocoelicaudia]]''.<ref name=hurumsabath2003/> Adults would have received little competition from small theropods such as [[troodontid]]s (''[[Borogovia]]'', ''[[Tochisaurus]]'', ''[[Saurornithoides]]''), [[oviraptorosaur]]s (''[[Elmisaurus]]'', ''[[Nemegtomaia]]'', ''[[Rinchenia]]'') or ''[[Bagaraatan]]'', sometimes considered a [[basal (phylogenetics)|basal]] [[tyrannosauroid]]. Other theropods, like the gigantic ''[[Therizinosaurus]]'', may have been [[herbivore|herbivorous]], and [[ornithomimosaur]]s such as ''[[Anserimimus]]'', ''[[Gallimimus]]'' and ''[[Deinocheirus]]'' might have been omnivores that only took small prey and were therefore no competition for ''Tarbosaurus''. However, as in other large tyrannosaurids as well as modern [[Komodo dragon]]s, juveniles and subadult ''Tarbosaurus'' may have filled niches between the massive adults and these smaller theropods.<ref name=holtz2004/>
==References==
{{reflist|2}}
==External links==
{{wikispecies|Tarbosaurus}}
{{portalpar|Dinosaurs}}
*[http://web.archive.org/web/20070125140546/staff.washington.edu/eoraptor/Tyrannosauroidea.html#Tarbosaurusbataar Discussion and specimen list] at The Theropod Database.
*[http://web.archive.org/web/20070110004506/http://www.paleograveyard.com/shanshanosaurus.html Skeletal image] of ''Shanshanosaurus'' at [http://web.archive.org/web/20070625232816/http://www.paleograveyard.com/main.html The Grave Yard].
*[http://www.dinosauria.com/jdp/trex/tyranno.htm Review of the Tyrannosauridae] by [[George Olshevsky]] (1995).
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[[Category:Cretaceous dinosaurs]]
[[Category:Dinosaurs of Asia]]
[[Category:Tyrannosaurs]]
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