Tarbosaurus

Bilateria

Tarbosaurus Temporal range: Late Cretaceous, 70 Ma PreЄ Є O S D C P T J K Pg N ↓
Mounted skeleton on exhibit in Cosmo Caixa, Barcelona
Scientific classification
Phylum:	Chordata
Class:	Reptilia
Superorder:	Dinosauria
Order:	Saurischia
Suborder:	Theropoda
Family:	†Tyrannosauridae
Subfamily:	†Tyrannosaurinae
Tribe:	†Tarbosaurini Olshevsky & Ford, 1995
Genus:	†Tarbosaurus Maleev, 1955
Species:	†T. bataar
Binomial name
Tarbosaurus bataar (Maleev, 1955) [originally Tyrannosaurus]
Synonyms
Genus synonymy Shanshanosaurus Dong, 1977 Maleevosaurus Carpenter, 1992 Jenghizkhan Olshevsky, 1995 Species synonymy Albertosaurus periculosus Riabinin, 1930 Alectrosaurus periculosus (Riabinin, 1930) Deinodon periculosus (Riabinin, 1930) Jenghizkhan periculosus (Riabinin, 1930) Tyrannosaurus bataar Maleev, 1955 Gorgosaurus novojilovi Maleev, 1955 Tarbosaurus efremovi Maleev, 1955 Gorgosaurus lancinator Maleev, 1955 Deinodon novojilovi (Maleev, 1955) Deinodon lancinator (Maleev, 1955) Aublysodon lancinator (Maleev, 1955) Charig, 1967 Aublysodon novojilovi (Maleev, 1955) Charig, 1967 Shanshanosaurus huoyanshanensis Dong, 1977 Tyrannosaurus efremovi (Maleev, 1955) Tarbosaurus novojilovi (Maleev, 1955) Aublysodon huoyanshanensis (Dong, 1977) Tyrannosaurus luanchuanensis Dong, 1979 Albertosaurus novojilovi (Maleev, 1955) Maleevosaurus novojilovi (Maleev, 1955) Jenghizkhan bataar (Maleev, 1955) Jenghizkhan luanchuanensis (Dong, 1979) Tyrannosaurus novojilovi (Maleev, 1955)

Tarbosaurus ( /ˌtɑrbɵˈsɔrəs/ tar-bo-sawr-əs; meaning "alarming lizard") is a genus of tyrannosaurid theropod dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period. Fossils 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 American genus Tyrannosaurus; if true, this would invalidate the genus Tarbosaurus altogether.

Tarbosaurus and Tyrannosaurus are considered to be at least closely related genera, if not 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 bipedal predator, weighing more than a 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

Adult (25 year old) and juvenile (2 year old) with a human for scale

Illustration of Tarbosaurus

Although smaller than Tyrannosaurus, Tarbosaurus was one of the largest tyrannosaurids. The largest known individuals were between 10 and 12 meters (30 to 40 ft) long.^[1] The mass of a fully grown individual is considered comparable to or slightly smaller than Tyrannosaurus.^[2]

The largest known Tarbosaurus skull is more than 1.3 meters (4 ft) long, larger than all other tyrannosaurids except Tyrannosaurus.^[2] 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 fenestrae (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, 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 crowns up to 85 millimeters (3.3 in) long. In the 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.^[3]

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 forelimbs, proportionably to body size the smallest of all members of the family. The hands had two clawed digits each, with an additional unclawed third metacarpal found in some specimens, similar to closely related genera. Holtz has suggested that Tarbosaurus also has a theropod reduction of fingers IV-I "developed further" than in other tyrannosaurids,^[4] as the second metacarpal in the Tarbosaurus specimens he studied is less than twice the length of the first metacarpal (other tyrannosaurids have a second metacarpal about twice the length of the first metacarpal). Also, the third metacarpal in Tarbosaurus is proportionally shorter than in other tyrannosaurids; in other tyrannosaurids (like Albertosaurus and Daspletosaurus), the third metacarpal is often longer than the first metacarpal, while in Tarbosaurus, the third metacarpal is shorter than the first.^[2]

In contrast to the forelimbs, 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.^[1][2]

Classification and systematics

Cladograms of Tyrannosauridae highlighting the position of Tarbosaurus Carr et al. 2005[5] Tyrannosauridae  void Albertosaurinae  Tyrannosaurinae  void Daspletosaurus  void  Tarbosaurus* Tyrannosaurus *Note: Carr et al. use the name Tyrannosaurus bataar Currie et al. 2003[6] Tyrannosauridae  void Albertosaurinae  Tyrannosaurinae  void void Daspletosaurus  void  Tarbosaurus Alioramus void Nanotyrannus Tyrannosaurus

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,^[5] and possibly the Mongolian genus Alioramus.^[3][6] 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 femurs than in the other subfamily, the Albertosaurinae.^[2]

Tarbosaurus bataar was originally described as a species of Tyrannosaurus,^[7] an arrangement that has been supported by more recent studies.^[5][8] Others prefer to keep the genera separate, while still recognizing them as sister taxa.^[2] 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 evolved in Asia and North America.^[3][6] The two known specimens 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.^[9]

Discovery and naming

Holotype skull PIN 551-1

In 1946, a joint Soviet-Mongolian expedition to the Gobi Desert in the Mongolian Ömnögovi Province turned up a large theropod skull and some vertebrae in the Nemegt Formation. In 1955, Evgeny Maleev, a Russian paleontologist, made this specimen the holotype (PIN 551-1) of a new species, which he called Tyrannosaurus bataar.^[7] The species name is a misspelling of the Mongolian баатар/baatar ("hero").^[3] 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"),^[10] 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.^[1]

A 1965 paper by A.K. Rozhdestvensky recognized all of Maleev's specimens as different 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.^[11] Later authors, including Maleev himself,^[12] agreed with Rozhdestvensky's analysis, although some used the name Tarbosaurus efremovi rather than T. bataar.^[13] 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.^[8] 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.^[14] A 1999 study subsequently reclassified Maleevosaurus as a juvenile Tarbosaurus.^[15] All research published since 1999 recognizes only a single species, which is either called Tarbosaurus bataar^[2][6][16] or Tyrannosaurus bataar.^[5]

After the original Russian-Mongolian expeditions in the 1940s, 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.^[3] Expeditions involving Japanese and Mongolian scientists between 1993 and 1998,^[17] as well as private expeditions hosted by Canadian paleontologist Phil Currie around the turn of the 21st century, discovered and collected further Tarbosaurus material.^[18][19] More than 30 specimens are known, including more than 15 skulls and several complete postcranial skeletons.^[2]

Possible synonyms

The pieces of IVPP V4878, described as Shanshanosaurus huoyanshanensis.

Chinese paleontologists discovered a partial skull and skeleton of a small theropod (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.^[20] Gregory Paul recognized Shanshanosaurus as a tyrannosaurid in 1988, referring it to the now-defunct genus Aublysodon.^[21] 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.^[22] 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 fragilis are often considered synonyms of Tarbosaurus.^[2]

Named in 1976 by Sergei Kurzanov, Alioramus is another genus of tyrannosaurid from slightly older sediments in Mongolia.^[23] Several analyses have concluded Alioramus was quite closely related to Tarbosaurus.^[3][6] 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.^[9]

Paleobiology

Restoration of an adult and subadult Tarbosaurus next to a human

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.^[24] Although Tarbosaurus has not been studied as thoroughly as the North American tyrannosaurids,^[3] the available material has allowed scientists to draw limited conclusions about its biology.

Skull mechanics

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 bones on top of the snout, which were firmly connected in the rear to the lacrimal bones by bony struts. These struts locked the two bones together, suggesting that force was then transmitted from the nasals to the lacrimals.^[3]

Skull seen from the front

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 and prefrontal bones in Tarbosaurus. The well-developed connections between the maxilla, lacrimal, frontal and prefrontal would have made its entire upper jaw more rigid.^[3]

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.^[3]

Some scientists have hypothesized that the more rigid skull of Tarbosaurus was an adaptation to hunting the massive titanosaurid sauropods 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.^[3]

Brain structure

Skull and neck of a mounted fossil

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 cast, called an endocast, of the inside of this cavity allowed Maleev to make preliminary observations about the shape of a Tarbosaurus brain.^[25] A newer polyurethane rubber cast allowed a more detailed study of Tarbosaurus brain structure and function.^[26]

Tyrannosaurus rex brain structure has also been analyzed,^[27] and Tarbosaurus was similar, differing only in the positions of some cranial nerve roots, including the trigeminal and accessory nerves. Tyrannosaurid brains were more similar to those of crocodilians and other reptiles than to birds. The total brain volume for a 12 meter (40 ft) Tarbosaurus is estimated at only 184 cubic centimeters (11.2 cu in). The large size of the olfactory bulbs, as well as the terminal and olfactory nerves, suggest that Tarbosaurus had a keen sense of smell, as was also the case with Tyrannosaurus. The vomeronasal bulb is large and differentiated from the olfactory bulb, indicating a well-developed Jacobsen's organ, which was used to detect pheromones. This may imply that Tarbosaurus had complex mating behavior. The auditory nerve was also large, suggesting good hearing, which may have been useful for auditory communication and spatial awareness. The nerve had a well-developed 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.^[26]

Paleopathology

In 2001, Bruce Rothschild and others published a study examining evidence for stress fractures and tendon avulsions in theropod dinosaurs and the implications for their behavior. Since stress fractures are caused by repeated trauma rather than singular events they are more likely to be caused by regular behavior than other types of injuries. None of the 18 Tarbosaurus foot bones examined in the study was found to have a stress fracture, but one of the 10 examined hand bones was found to have one. Stress fractures in the hands have special behavioral significance compared to those found in the feet since stress fractures there can be obtained while running or during migration. Hand injuries, by contrast, are more likely to be obtained while in contact with struggling prey. The presence of stress fractures and tendon avulsions in general provide evidence for a "very active" predation-based diet rather than obligate scavenging.^[28]

Paleoecology

Ömnögovi Province, the Mongolian aimag where most Tarbosaurus remains have been discovered

The vast majority of known Tarbosaurus fossils were recovered from the Nemegt Formation in the Gobi Desert of southern Mongolia. This geologic formation has never been dated radiometrically, but the fauna present in the fossil record indicate it was probably deposited during the early Maastrichtian stage, at the end of the Late Cretaceous^[24] about 70 million years ago.^[29][30] The Subashi Formation, in which Shanshanosaurus remains were discovered, is also Maastrichtian in age.^[31]

Nemegt sediments preserve large river channels and soil deposits that indicate a far more humid climate than those suggested by the underlying Barun Goyot and Djadochta Formations. However, 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.^[24] Crocodilians included several species of Shamosuchus, a genus with teeth adapted for crushing shells.^[32] Mammal fossils are exceedingly rare in the Nemegt Formation, but many birds have been found, including the enantiornithine Gurilynia and the hesperornithiform Judinornis, as well as Teviornis, an early representative of the still-existing Anseriformes (waterfowl), a bird order. Scientists have described many dinosaurs from the Nemegt Formation, including ankylosaurids such as Tarchia, and pachycephalosaurs such as Homalocephale and Prenocephale.^[24] By far the largest predator known from the formation, adult Tarbosaurus most likely preyed upon large hadrosaurs such as Saurolophus and Barsboldia, or sauropods such as Nemegtosaurus, and Opisthocoelicaudia.^[3] Adults would have received little competition from small theropods such as troodontids (Borogovia, Tochisaurus, Saurornithoides), oviraptorosaurs (Elmisaurus, Nemegtomaia, Rinchenia) or Bagaraatan, sometimes considered a basal tyrannosauroid. Other theropods, like the gigantic Therizinosaurus, may have been herbivorous, and ornithomimosaurs 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 dragons, juveniles and subadult Tarbosaurus may have filled niches between the massive adults and these smaller theropods.^[2]

References

1. ^ ^{a b c} Maleev, Evgeny A. (1955). "New carnivorous dinosaurs from the Upper Cretaceous of Mongolia." (in Russian). Doklady Akademii Nauk SSSR 104 (5): 779–783. 
2. ^ ^{a b c d e f g h i j} Holtz, Thomas R. (2004). "Tyrannosauroidea". In Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.). The Dinosauria (Second ed.). Berkeley: University of California Press. pp. 111–136. ISBN 0-520-24209-2. 
3. ^ ^{a b c d e f g h i j k l} Hurum, Jørn H.; and Sabath, Karol. (2003). "Giant theropod dinosaurs from Asia and North America: Skulls of Tarbosaurus bataar and Tyrannosaurus rex compared" (PDF). Acta Palaeontologica Polonica 48 (2): 161–190. http://www.app.pan.pl/archive/published/app48/app48-161.pdf. 
4. ^ Carpenter K, Tanke D.H. & Skrepnick M.W. (2001), Mesozoic Vertebrate Life (Indiana University Press, ISBN 0-253-33907-3), p. 71.
5. ^ ^{a b c d} Carr, Thomas D.; Williamson, Thomas E.; and Schwimmer, David R. (2005). "A new genus and species of tyrannosauroid from the Late Cretaceous (middle Campanian) Demopolis Formation of Alabama". Journal of Vertebrate Paleontology 25 (1): 119–143. doi:10.1671/0272-4634(2005)025[0119:ANGASO]2.0.CO;2. 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. 
6. ^ ^{a b c d e} Currie, Philip J.; Hurum, Jørn H; and Sabath, Karol. (2003). "Skull structure and evolution in tyrannosaurid phylogeny" (PDF). Acta Palaeontologica Polonica 48 (2): 227–234. http://www.app.pan.pl/archive/published/app48/app48-227.pdf. 
7. ^ ^{a b} Maleev, Evgeny A. (1955). "Giant carnivorous dinosaurs of Mongolia". Doklady Akademii Nauk SSSR 104 (4): 634–637. 
8. ^ ^{a b} Carpenter, Ken. (1992). "Tyrannosaurids (Dinosauria) of Asia and North America". In Mateer, Niall J.; and Chen Peiji (eds.). Aspects of Nonmarine Cretaceous Geology. Beijing: China Ocean Press. pp. 250–268. 
9. ^ ^{a b} Currie, Philip J. (2003). "Cranial anatomy of tyrannosaurids from the Late Cretaceous of Alberta" (PDF). Acta Palaeontologica Polonica 48 (2): 191–226. http://app.pan.pl/acta48/app48-191.pdf. 
10. ^ Liddell, Henry G.; and Scott, Robert (1980). Greek–English Lexicon (Abridged ed.). Oxford: Oxford University Press,. ISBN 0-19-910207-4. 
11. ^ Rozhdestvensky, Anatoly K. (1965). "Growth changes in Asian dinosaurs and some problems of their taxonomy". Paleontological Journal 3: 95–109. 
12. ^ Maleev, Evgeny A. (1974). "Gigantic carnosaurs of the family Tyrannosauridae". The Joint Soviet-Mongolian Paleontological Expedition Transactions 1: 132–191. 
13. ^ Barsbold, Rinchen. (1983). "Carnivorous dinosaurs from the Cretaceous of Mongolia". The Joint Soviet-Mongolian Paleontological Expedition Transactions 19: 5–119. 
14. ^ Olshevsky, George; and Ford, Tracy L. (1995). "The origin and evolution of the tyrannosaurids, part 1" (in Japanese). Dinosaur Frontline 9: 92–119. 
15. ^ Carr, Thomas D. (1999). "Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria)". Journal of Vertebrate Paleontology 19 (3): 497–520. doi:10.1080/02724634.1999.10011161. http://www.vertpaleo.org/publications/jvp/19-497-520.cfm. 
16. ^ Xu Xing, X; Norell, Mark A.; Kuang Xuewen; Wang Xiaolin;, Zhao Qi; and Jia Chengkai. (2004). "Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids". Nature 431 (7009): 680–684. doi:10.1038/nature02855. PMID 15470426. 
17. ^ Watabe, Masato; and Suzuki, Shigeru. (2000). "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". Hayashibara Museum of Natural Sciences Research Bulletin 1: 99–108. 
18. ^ Currie, Philip J. (2001). "Nomadic Expeditions, Inc., report of fieldwork in Mongolia, September 2000.". Alberta Palaeontological Society, Fifth Annual Symposium, Abstract Volume. Calgary: Mount Royal College. pp. 12–16. 
19. ^ Currie, Philip J. (2002). "Report on fieldwork in Mongolia, September 2001.". Alberta Palaeontological Society, Sixth Annual Symposium, "Fossils 2002," Abstract Volume. Calgary: Mount Royal College. pp. 8–12. 
20. ^ Dong Zhiming. (1977). "On the dinosaurian remains from Turpan, Xinjiang" (in Chinese). Vertebrata PalAsiatica 15: 59–66. 
21. ^ Paul, Gregory S. (1988). Predatory Dinosaurs of the World. New York: Simon & Schuster. pp. 464pp. 
22. ^ Currie, Philip J.; and Dong Zhiming. (2001). "New information on Shanshanosaurus huoyanshanensis, a juvenile tyrannosaurid (Theropoda, Dinosauria) from the Late Cretaceous of China". Canadian Journal of Earth Sciences 38 (12): 1729–1737. doi:10.1139/cjes-38-12-1729. 
23. ^ Kurzanov, Sergei M. (1976). "A new Late Cretaceous carnosaur from Nogon−Tsav, Mongolia" (in Russian). The Joint Soviet-Mongolian Paleontological Expedition Transactions 3: 93–104. 
24. ^ ^{a b c d} Jerzykiewicz, Tomasz; and Russell, Dale A. (1991). "Late Mesozoic stratigraphy and vertebrates of the Gobi Basin". Cretaceous Research 12 (4): 345–377. doi:10.1016/0195-6671(91)90015-5. 
25. ^ Maleev, Evgeny A. (1965). "On the brain of carnivorous dinosaurs" (in Russian). Paleontological Journal 2: 141–143. 
26. ^ ^{a b} Saveliev, Sergei V.; and Alifanov, Vladimir R. (2005). "A new study of the brain of the predatory dinosaur Tarbosaurus bataar (Theropoda, Tyrannosauridae)". Paleontological Journal 41 (3): 281–289. doi:10.1134/S0031030107030070. 
27. ^ Brochu, Christopher A. (2000). "A digitally-rendered endocast for Tyrannosaurus rex". Journal of Vertebrate Paleontology 20 (1): 1–6. doi:10.1671/0272-4634(2000)020[0001:ADREFT]2.0.CO;2. http://www.bioone.org/perlserv/?request=get-toc&issn=0272-4634&volume=20&issue=1. 
28. ^ Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 331-336.
29. ^ Sulliban, R.M. (2006). "A taxonomic review of the Pachycephalosauridae (Dinosauria: Ornithischia)." Pp. 347-366 in Lucas, S.G. and Sullivan, R.M. (eds.), Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 3.
30. ^ Gradstein, Felix M.; Ogg, James G.; and Smith, Alan G. (2005). A Geologic Time Scale 2004. Cambridge: Cambridge University Press. pp. 500pp. ISBN 978-0521781428. 
31. ^ Shen Y.B.; and Mateer, Niall J. (1992). "An outline of the Cretaceous System in northern Xinjiang, western China". In Mateer, Niall J.; and Chen Peiji (eds.). Aspects of Nonmarine Cretaceous Geology. Beijing: China Ocean Press. pp. 49–77. 
32. ^ Efimov, Mikhail B. (1983). "Revision of the fossil crocodiles of Mongolia." (in Russian). The Joint Soviet-Mongolian Paleontological Expedition Transactions 24: 76–95. 

External links

Dinosaurs portal

Images and photos.

• Skeletal image of Shanshanosaurus at The Grave Yard.
• Comparison between Tarbosaurus skulls from specimens of different age group and size.

Readable material.

• Discussion and specimen list at The Theropod Database.
• Review of the Tyrannosauridae by George Olshevsky (1995).
• Scienceblogs: Juvenile, 5 years old Tarbosaurus specimen found in Mongolia 2006.