Alioramus

Alioramus (/ˌælioʊˈreɪməs/; meaning 'different branch') is a genus of tyrannosaurid theropod dinosaurs from the Late Cretaceous period of Asia. The type species, A. remotus, is known from a partial skull and three foot bones recovered from Mongolian sediments which were deposited in a humid floodplain about 70 million years ago. These remains were named and described by Soviet paleontologist Sergei Kurzanov in 1976. A second species, A. altai, known from a much more complete skeleton, was named and described by Stephen L. Brusatte and colleagues in 2009. Its relationships to other tyrannosaurid genera are unclear, with some evidence supporting a hypothesis that Alioramus is closely related to the contemporary species Tarbosaurus bataar.

Alioramus were bipedal like all known theropods, and their sharp teeth indicate that they were carnivores. Known specimens were smaller than other tyrannosaurids like Tarbosaurus bataar and Tyrannosaurus rex, but their adult size is difficult to estimate since both Alioramus species are known only from juvenile or sub-adult remains. The recent discovery of Qianzhousaurus indicates that it belongs to a distinct branch of tyrannosaur.[2] The genus Alioramus is characterized by a row of five bony crests along the top of the snout, a greater number of teeth than any other genus of tyrannosaurid, and a lower skull than most other tyrannosaurids.

Alioramus
Temporal range: Late Cretaceous, 70 Ma
Texas Alioramus
Skeleton mount at Texas A&M University-Commerce
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Family: Tyrannosauridae
Tribe: Alioramini
Genus: Alioramus
Kurzanov, 1976
Type species
Alioramus remotus
Kurzanov, 1976
Species

A. remotus Kurzanov, 1976
A. altai Brusatte et al., 2009

Synonyms

Description

Alioramus skeletal steveoc
Size of A. remotus compared with a human

Alioramus remotus was estimated at 5 to 6 metres (16 to 20 ft) in length when originally described by Sergei Kurzanov in 1976.[3] Kurzanov, however, did not correct for lengthening of the skull by deformation during fossilization, which may indicate a shorter overall body length for this individual. If this specimen is a juvenile, then adult Alioramus would have reached greater lengths, but no confirmed adult specimens are known.[4]

The skull of A. remotus was approximately 45 centimetres (18 in) long.[5] In general, it is long and low, a shape typical of more basal tyrannosauroids and juveniles of larger tyrannosaurids. The premaxillary bones at the tip of the snout in Alioramus remotus have not been found, but are taller than wide in all tyrannosauroids for which they are known.[4] The nasal bones are fused and ornamented with a row of five irregular bony crests that protrude upwards from the midline, where the nasal bones are sutured together. These crests all measure more than 1 centimetre (0.39 in) tall.[3]

Alioramus Life Restoration
Artist's impression of A. remotus

At the back of the skull there is a protrusion, called the nuchal crest, arising from the fused parietal bones, a feature shared with all tyrannosaurids. In Alioramus, the nuchal crest is greatly thickened, similarly to Tarbosaurus and Tyrannosaurus. Like the rest of the skull, the lower jaw of Alioramus was long and slender, another possible juvenile characteristic.[4] As in Tarbosaurus, a ridge on the outer surface of the angular bone of the lower jaw articulated with the rear of the dentary bone, locking the two bones together and removing much of the flexibility seen in other tyrannosaurids.[6] Other tyrannosaurids had four premaxillary teeth, D-shaped in cross section, on each side. Including 16 or 17 in each maxilla, and 18 in each dentary, Alioramus had 76 or 78 teeth, more than any other tyrannosaurid.[7] The braincase of A. altai was intermediate between the basal theropod and avialan conditions.[8]

The rest of the skeleton of Alioramus remotus is completely unknown except for three metatarsals (bones of the upper foot), but the discovery of A. altai, which is known from substantially more complete remains, has shed light on the anatomy of the genus.[9]

Classification and systematics

Paleontologists have long classified Alioramus within the superfamily Tyrannosauroidea, but because its remains were for many years poorly known, a more precise classification had remained elusive until the discovery of A. altai.[4] A cladistic analysis published in 2003 found Alioramus could be further classified into the family Tyrannosauridae and the subfamily Tyrannosaurinae, alongside Tyrannosaurus, Tarbosaurus and Daspletosaurus.[10] A 2004 study supported this result but suggested it was equally probable that Alioramus belonged outside the family Tyrannosauridae entirely, with its supposed juvenile characters actually reflecting a more basal position within Tyrannosauroidea.[4] Another study omitted Alioramus altogether due to the only specimen's fragmentary nature.[11] The discovery of A. altai in 2009 confirmed the placement of the genus within the Tyrannosaurinae.[9]

Alioramus skull steveoc
A. remotus skull diagram, known portions in white
Endocranial cast of Alioramus altai
Endocranial cast of Alioramus altai

Tarbosaurus and Alioramus shared several skull features, including a locking mechanism in the lower jaw between the dentary and angular bones, and both lacked the prong of the nasal bones which connected to the lacrimal bones in all other tyrannosaurids except adult Daspletosaurus. The two genera may be closely related, representing an Asian branch of the Tyrannosauridae.[6][10] Some specimens of Tarbosaurus have a row of bumps on the nasal bones like those of Alioramus, although much lower. The long and low shape of the only known Alioramus remotus skull indicated that it was immature when it died and might even have been a juvenile Tarbosaurus, which lived in the same time and place. The more prominent nasal crests and much higher tooth count of Alioramus, however, suggested it was a separate taxon, even if it is known only from juvenile remains,[7] confirmed by the discovery of A. altai.[9] Specimens identified as immature Tarbosaurus have the same tooth count as adults.[12][13]

Recently a cladogram has been published finding Alioramus just outside Tyrannosauridae. Below is the cladogram by Loewen (2013).[14]

Dilong paradoxus Dilong TJV 50

Eotyrannus lengi

Bagaraatan ostromi

Raptorex kriegsteini

Dryptosaurus aquilunguis Dryptosaurus by Durbed

Alectrosaurus olseni Alectrosaurus flipped

Xiongguanlong baimoensis Xiongguanlong remains 01

Appalachiosaurus montgomeriensis Appalachiosaurus montgomeriensis flipped

Alioramus altai

Alioramus remotus Alioramus Life Restoration flipped.jpg

Tyrannosauridae Gorgosaurus flipped

Discovery and naming

Alioramus, Tyrannosauridae. Late Cretaceous (68mya) from Mongolia
Skull at Wyoming Dinosaur Center, Thermopolis

The holotype (PIN 3141/1) of Alioramus is a partial skull associated with three metatarsals. A joint Soviet-Mongolian expedition to the Gobi Desert in the early 1970s found these remains at a locality known as Nogon-Tsav in the Mongolian province of Bayankhongor. Alioramus was named and described by Russian paleontologist Sergei Kurzanov in 1976. Its crests and low skull profile looked so different from other tyrannosaurids that Kurzanov believed his find was far removed from other members of the family. Accordingly, he gave it the generic name Alioramus, derived from the Latin alius ('other') and ramus ('branch'), and the specific name A. remotus, which means 'removed' in Latin.[3] Alioramus is known from the holotypes of A. remotus[4] and A. altai.[9]

Paleoecology

Map mn bayankhongor aimag
Bayankhongor, the Mongolian aimag (province) where Alioramus remains were discovered

The Beds of Nogon-Tsav are considered to be the same age as the Nemegt Formation.[3] This geologic formation has never been 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.[15]

The Maastrichtian stage in Mongolia, as preserved in the Nemegt Formation and at Nogon-Tsav, was characterized by a wetter and more humid climate compared with the semi-arid environment preserved in the earlier, underlying Barun Goyot and Djadochta Formations. Nemegt sediments preserve floodplains, large river channels and soil deposits, but caliche deposits indicate periodic droughts.[16] This environment supported a more diverse and generally larger dinosaur fauna than in earlier times. Kurzanov reported that other theropods, including Tarbosaurus, ornithomimosaurs and therizinosaurs were discovered at the same locality,[3] but these remains have never been reported in detail. If the Nogon Tsav fauna was similar to that of the Nemegt Formation, troodontid theropods, as well as pachycephalosaurs, ankylosaurids and hadrosaurs would also have been present.[15] Titanosaurian sauropods were also potential prey for predators in the Nemegt.[6]

See also

References

  1. ^ Carr, Thomas D.; Varricchio, David J.; Sedlmayr, Jayc C.; Roberts, Eric M.; Moore, Jason R. (2017). "A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system". Scientific Reports. 7: 44942. doi:10.1038/srep44942. PMC 5372470. PMID 28358353.
  2. ^ Junchang Lü; Laiping Yi; Stephen L. Brusatte; Ling Yang; Hua Li; Liu Chen (7 May 2014). "A new clade of Asian Late Cretaceous long-snouted tyrannosaurids". Nature Communications. 5 (3788): 3788. doi:10.1038/ncomms4788. PMID 24807588.
  3. ^ a b c d e Kurzanov, Sergei M. "A new carnosaur from the Late Cretaceous of Nogon-Tsav, Mongolia". The Joint Soviet-Mongolian Paleontological Expedition Transactions (in Russian). 3: 93–104.
  4. ^ a b c d e f Holtz, Thomas R. (2004). "Tyrannosauroidea". In Weishampel, David B.; Dodson, Peter; Osmólska, Halszka. The Dinosauria (Second ed.). Berkeley: University of California Press. pp. 111–136. ISBN 978-0-520-24209-8.
  5. ^ Currie, Philip J. (2000). "Theropods from the Cretaceous of Mongolia". The Age of Dinosaurs in Russia and Mongolia. Cambridge: Cambridge University Press. pp. 434–455. ISBN 978-0-521-54582-2.
  6. ^ a b c Hurum, Jørn H.; Sabath, Karol (2003). "Giant theropod dinosaurs from Asia and North America: Skulls of Tarbosaurus bataar and Tyrannosaurus rex compared". Acta Palaeontologica Polonica. 48 (2): 161–190.
  7. ^ a b Currie, Philip J. (2003). "Cranial anatomy of tyrannosaurids from the Late Cretaceous of Alberta". Acta Palaeontologica Polonica. 48 (2): 191–226.
  8. ^ "Variation, Variability, and the Origin of the Avian Endocranium: Insights from the Anatomy of Alioramus altai (Theropoda: Tyrannosauroidea)". PLOS Collections. doi:10.1371/journal.pone.0023393;jsessionid=B5ED8399160D7F46A7647ADE513F5B9C.ambra01 (inactive 2018-08-06). Retrieved 2012-11-09.
  9. ^ a b c d Brusatte, Stephen L.; Carr, Thomas D.; Erickson, Gregory M.; Bever, Gabe S.; Norell, Mark A. (2009). "A long-snouted, multihorned tyrannosaurid from the Late Cretaceous of Mongolia". Proceedings of the National Academy of Sciences of the United States of America. 106 (41): 17261–6. doi:10.1073/pnas.0906911106. PMC 2765207. PMID 19805035.
  10. ^ a b Currie, Philip J.; Hurum, Jørn H; Sabath, Karol (2003). "Skull structure and evolution in tyrannosaurid phylogeny". Acta Palaeontologica Polonica. 48 (2): 227–234.
  11. ^ Carr, Thomas D.; Williamson, Thomas E.; 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.
  12. ^ Maleev, Evgeny A. (1955). "New carnivorous dinosaurs from the Upper Cretaceous of Mongolia". Doklady Akademii Nauk SSSR (in Russian). 104 (5): 779–783.
  13. ^ Currie, Philip J. (2003). "Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia". Canadian Journal of Earth Sciences. 40 (4): 651–665. doi:10.1139/e02-083.
  14. ^ Loewen, M.A.; Irmis, R.B.; Sertich, J.J.W.; Currie, P. J.; Sampson, S. D. (2013). Evans, David C, ed. "Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans". PLoS ONE. 8 (11): e79420. doi:10.1371/journal.pone.0079420. PMC 3819173. PMID 24223179.
  15. ^ a b Jerzykiewicz, Tomasz; 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.
  16. ^ Osmólska, Halszka (1997). "Nemegt Formation". In Currie, Philip J.; Kevin Padian. The Encyclopedia of Dinosaurs. San Diego: Academic Press. pp. 471–472. ISBN 978-0-12-226810-6.

External links

Albertosaurinae

Albertosaurines, or dinosaurs of the subfamily Albertosaurinae, lived in the Late Cretaceous of United States and Canada. The subfamily was first used by Philip J. Currie, Jørn H. Hurum and Karol Sabath as a group of tyrannosaurid dinosaurs. It was originally defined as "(Albertosaurus + Gorgosaurus)", including only the two genera. The group is sister clade to Tyrannosaurinae. In 2007, it was found that the group also contained Maleevosaurus, often synonymized with Tarbosaurus. However, this classification has not been accepted, and Maleevosaurus is still considered a juvenile Tarbosaurus or Tyrannosaurus. Clevenger T. M. McLain found in an abstract, that Alioramus, commonly used as a derived tyrannosauroid, was an albertosaurine, or the sister taxon to the group.

Appalachiosaurus

Appalachiosaurus ( ap-ə-LAY-chee-o-SAWR-əs; "Appalachian lizard") is a genus of tyrannosauroid theropod dinosaur from the Late Cretaceous Period of eastern North America. Like almost all theropods, it was a bipedal predator. Only a juvenile skeleton has been found, representing an animal over 7 meters (23 ft) long and weighing over 600 kilograms (1300 lb), which indicates an adult would have been even larger. It is the most completely known theropod from the eastern part of North America.

Fossils of Appalachiosaurus were found in central Alabama, from the Demopolis Chalk Formation. This formation dates to the middle of the Campanian stage of the Late Cretaceous, or around 77 million years ago. Fossil material assigned to A. montegomeriensis is also known from the Donoho Creek and Tar Heel-Coachman formations of North and South Carolina.

Bagaraatan

Bagaraatan (/'ba-ɣa-raa-tan/ meaning 'small' baɣa + 'carnivorous animal, beast of prey' araatan in Mongolian) is a genus of theropod dinosaur from the Late Cretaceous period. Its fossils were found in the Nemegt Formation of Mongolia. Bagaraatan may have been around 3 to 4 metres (9.8 to 13 ft) in length.

The type species, B. ostromi, was described by Osmolska in 1996. The post-cranial (ZPAL MgD-I/108) skeleton has been described as "bird-like", while the skull exhibits features of several different theropod groups.

Dilong paradoxus

Dilong (帝龍, which means 'emperor dragon') is a genus of basal tyrannosauroid dinosaur. The only species is Dilong paradoxus. It is from the Lower Cretaceous Yixian Formation near Lujiatun, Beipiao, in the western Liaoning province of China. It lived about 126 million years ago.

Dynamoterror

Dynamoterror is a genus of tyrannosaurid theropod dinosaur that lived in what is now New Mexico during the Late Cretaceous Period, approximately 78 million years ago. The type species is Dynamoterror dynastes. The generic name is derived from the Greek word dynamis (δύναμις) meaning "power" and the Latin word terror. The specific name is derived from δυνάστης, "ruler".

Eotyrannus

Eotyrannus (meaning "dawn tyrant") is a genus of tyrannosauroid theropod dinosaur hailing from the Early Cretaceous Wessex Formation beds, included in Wealden Group, located in the southwest coast of the Isle of Wight, United Kingdom. The remains (MIWG1997.550), consisting of assorted skull, axial skeleton and appendicular skeleton elements, from a juvenile or subadult, found in a plant debris clay bed, were described by Hutt et al. in early 2001. The etymology of the generic name refers to the animals classification as an early tyrannosaur or "tyrant lizard", while the specific name honors the discoverer of the fossil.

Juratyrant

Juratyrant (meaning "Jurassic tyrant") is a tyrannosauroid dinosaur genus from the late Jurassic period (early Tithonian age) of England. The genus contains a single species, J. langhami.

Karol Sabath

Karol Sabath (April 24, 1963 – October 10, 2007) was a Polish biologist, paleontologist and paleoartist.

He was employed by the Instytut Paleobiologii of the Polska Akademia Nauk - Institute of Paleobiology, Polish Academy of Sciences, Warsaw. He also worked for National Geographic magazine, the Museum of the Polish Geological Institute, the European edition of Scientific American, and various other publishing houses in Poland.

He authored many popular-science books for children, did translations, and wrote popular-science articles for Polish national newspapers.

He was a scientific advisor for many popular-science events, including reconstructions of paleobiological environment and specimens (Baltow Jurassic Park).

He was a member of one of the Polish - Mongolian Paleobiological Expeditions to the Gobi Desert. His scientific interests included dinosaur eggs and babies, and dinosaur tracks.

In 2003, Sabath and Jørn Hurum demonstrated that Tarbosaurus is a close relative of Alioramus, and not a species of Tyrannosaurus. This was based on supporting evidence for the hypothesis that tyrannosaurids originated in Asia, and then migrated to North America.

He was a co-founder of Polish Evolutionary Wortal ewolucja.org and Paleobiology Website paleontologia.pl

He was a Wikipedia Editor and DMOZ Editor.

Kileskus

Kileskus (meaning lizard in the Khakas language) is a genus of tyrannosauroid dinosaur known from partial remains found in Middle Jurassic (Bathonian stage) Itat Formation of Krasnoyarsk Krai, Russia. Fossils recovered include the holotype maxilla, a premaxilla, a surangular, and a few bones from the hand and foot. The skull bones are similar to those of Proceratosaurus. The type species is K. aristotocus. Kileskus was named in 2010 by Averianov and colleagues.

List of Asian dinosaurs

This is a list of dinosaurs whose remains have been recovered from Asia excluding the Indian Subcontinent, which was part of a separate landmass for much of the Mesozoic. This list does not include dinosaurs that live or lived after the Mesozoic age such as birds.

Nemegt Formation

The Nemegt Formation (or Nemegtskaya Svita) is a geological formation in the Gobi Desert of Mongolia, dating to the Late Cretaceous. It overlies and sometimes interfingers with the Barun Goyot Formation. Interfingering has been noted at the stratotype (Red Walls) and Khermeen Tsav. It consists of river channel sediments and contains fossils of fish, turtles, crocodilians, and a diverse fauna of dinosaurs, including birds. The climate associated with it was wetter than when preceding formations were deposited; there seems to have existed at least some degree of forest cover. Fossilized trunks have been also found.

There has been no absolute dating of the Nemegt Formation. It is, however, almost certainly early Maastrichtian c 71-70 Ma. Gradzinski and others considered a Campanian age possible but more recent research indicates otherwise. A Campanian age no longer seems credible, because the Alagteegian (or lower Djadokhtan, at the locality "Chuluut Uul") has been radiometrically dated at about 73.5 Ma or even younger (a more recent K/Ar date is 71.6 +/- 1.6 Ma). The c 73.5 (or perhaps 72) Ma Alagteegian is separated from the Nemegt by the "classic" Djadokhtan (e.g. Bayan Dzag), later Djadohktan (represented by Ukhaa Tolgod) and Barungoyotian (Khulsan). All these intervening horizons almost certainly represent more than the 1.5 million years between the dated Alagteegian level and the onset of Maastrichtian time (72.1 million Ma according to current dating). Ergo the Nemegt is entirely Maastrichtian. See also Shuvalov, Sochava and Martinsson The Age of Dinosaurs in Russia and Mongolia. The presence of Saurolophus further supports an early Maastrichtian age as the same genus occurs in the early Maastrichtian Horseshoe Canyon formation.

Proceratosaurus

Proceratosaurus is a genus of small-sized (~3 metres (9.8 ft) long) carnivorous theropod dinosaur from the Middle Jurassic (Bathonian) of England. It was originally thought to be an ancestor of Ceratosaurus, due to the similar small crest on its snout. Now, however, it is considered a coelurosaur, specifically one of the earliest known members of Tyrannosauroidea, the clade of basal relatives of the tyrannosaurs.The type specimen is held in the London Museum of Natural History and was recovered in 1910 at Minchinhampton while excavating for a reservoir.

Qianzhousaurus

Qianzhousaurus is a genus of tyrannosaurid dinosaur. There is currently only one species named, the type species Qianzhousaurus sinensis. Nicknamed "Pinocchio rex" for its long snout in comparison with other known tyrannosaurs. It was discovered in southern China and first published in the journal Nature Communications in May 2014.

Aside from its signature snout, it also had long, narrow teeth, while in comparison, relatives like Tyrannosaurus had thick teeth and powerful, deep-set jaws. The bones of Qianzhousaurus were discovered by workmen at a construction site near the city of Ganzhou, who then took them to a local museum.Lead author Lü Junchang from the Institute of Geology, Chinese Academy of Geological Sciences stated that "the new discovery is very important. Along with Alioramus from Mongolia, it shows that the long-snouted tyrannosaurids were widely distributed in Asia. Although we are only starting to learn about them, the long-snouted tyrannosaurs were apparently one of the main groups of predatory dinosaurs in Asia." The existence of long-snouted tyrannosaurs was previously suspected due to other inconclusive fossil finds, that could be explained as the juveniles of short-snouted species, but co-author Stephen L. Brusatte from the University of Edinburgh reveals that the find "tells us pretty unequivocally that these long-snouted tyrannosaurs were a real thing. They were a different breed, living right at the end of the age of dinosaurs."

Examination of the rock encasing the fossil shows it is probably from the Red Beds of the Nanxiong Formation, which date to the Cretaceous–Paleogene boundary about 72-66 million years ago.

Sergei Kurzanov

Sergei Mikhailovich Kurzanov (Сергей Михайлович Курзанов, born 1947) is a Russian (formerly Soviet) paleontologist at the Paleontological Institute of the Russian Academy of Sciences. He is known mainly for his work in Mongolia and the ex-Soviet republics in Central Asia. In 1976 he announced the discovery of Alioramus. In 1981 he announced the discovery of Avimimus.In 1998 a species of iguanodont dinosaur from Mongolia was named Altirhinus kurzanovi in his honor.

Sinotyrannus

Sinotyrannus (meaning "Chinese tyrant") is a genus of large basal proceratosaurid dinosaur, a relative of tyrannosaurids which flourished in North America and Asia during the Jurassic and early Cretaceous periods. Sinotyrannus is known from a single incomplete fossil specimen including a partial skull, from the Early Cretaceous Jiufotang Formation of Liaoning, China. Though it is not much younger than primitive tyrannosauroids such as Dilong, it is similar in size to later forms such as Tyrannosaurus. It was much larger than contemporary tyrannosauroids; reaching a total estimated length of 9–10 m (30–33 ft), it is the largest known theropod from the Jiufotang Formation. The type species is S. kazuoensis, described by Ji et al., in 2009.

Stokesosaurus

Stokesosaurus (meaning "Stokes' lizard") is a genus of small (around 3 to 4 meters (10 to 13 ft) in length), carnivorous early tyrannosauroid theropod dinosaurs from the late Jurassic period of Utah, United States.

Tarbosaurus

Tarbosaurus ( TAR-bə-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 see this species as an Asian representative of the North American genus Tyrannosaurus; this would make the genus Tarbosaurus redundant. Tarbosaurus and Tyrannosaurus, if not synonymous, are considered to be at least closely related genera. 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 up to five tonnes and equipped with about sixty large 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, probably preying on other large dinosaurs like the hadrosaur Saurolophus or the sauropod Nemegtosaurus. Tarbosaurus is represented by dozens of fossil specimens, including several complete skulls and skeletons. These remains have allowed scientific studies focusing on its phylogeny, skull mechanics, and brain structure.

Tyrannosauridae

Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three. All of these animals lived near the end of the Cretaceous Period and their fossils have been found only in North America and Asia.

Although descended from smaller ancestors, tyrannosaurids were almost always the largest predators in their respective ecosystems, putting them at the apex of the food chain. The largest species was Tyrannosaurus rex, one of the largest known land predators, which measured up to 12.3 metres (40 ft) in length and according to most modern estimates 8.4 metric tons (9.3 short tons) to 14 metric tons (15.4 short tons) in weight. Tyrannosaurids were bipedal carnivores with massive skulls filled with large teeth. Despite their large size, their legs were long and proportioned for fast movement. In contrast, their arms were very small, bearing only two functional digits.

Unlike most other groups of dinosaurs, very complete remains have been discovered for most known tyrannosaurids. This has allowed a variety of research into their biology. Scientific studies have focused on their ontogeny, biomechanics and ecology, among other subjects. Soft tissue has been reported from one specimen of Tyrannosaurus rex.

Xiongguanlong

Xiongguanlong ("Grand Pass dragon") is a genus of tyrannosauroid dinosaur that lived in the Early Cretaceous of what is now China. The type species is X. baimoensis, described online in 2009 by a group of researchers from China and the United States, and formally published in January 2010. The genus name refers to the city of Jiayuguan, a city in northwestern China. The specific name is derived from bai mo, "white ghost", after the "white ghost castle", a rock formation near the fossil site. The fossils include a skull, vertebrae, a right ilium and the right femur. The rocks it was found in are from the Aptian to Albian stages of the Cretaceous, between 125 and 100 million years ago.

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