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tarbosaurus (pronounced /ˌtɑrbɵˈsɔrəs/ tar-bo-sawr-əs; meaning \\\\\\\\\\\\\\\"terrifying lizard\\\\\\\\\\\\\\\") is a genus of tyrannosaurid theropod dinosaur that flourished in asia between 70 and 65 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 closely related genera, even if they are 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.

a tarbosaurus skull
although smaller than tyrannosaurus, tarbosaurus was one of the largest tyrannosaurids. the largest known individuals were between 10 and 12 meters (33 to 40 ft) long, each with a head held up to 5 meters (16.5 ft) above the ground.[1] the mass of a fully grown individual has never been published, although it 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, 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.[1][2]
[edit]classification and systematics

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,[4] and possibly the mongolian genus alioramus.[3][5] 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,[6] an arrangement that has been supported by more recent studies.[4][7] 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][5] 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.[8]
[edit]discovery and naming

ömnögovi province, the mongolian aimag where most tarbosaurus remains have been discovered
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.[10] later authors, including maleev himself,[11] agreed with rozhdestvensky\\\\\\\\\\\\\\\'s analysis, although some used the name tarbosaurus efremovi rather than t. bataar.[12] 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.[7] 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.[13] a 1999 study subsequently reclassified maleevosaurus as a juvenile tarbosaurus.[14] all research published since 1999 recognizes only a single species, which is either called tarbosaurus bataar[2][5][15] or tyrannosaurus bataar.[4]
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,[16] as well as private expeditions hosted by canadian paleontologist phil currie around the turn of the 21st century, discovered and collected further tarbosaurus material.[17][18] more than 30 specimens are known, including more than 15 skulls and several complete postcranial skeletons.[2]
[edit]possible synonyms