Tarbosaurus is a genus of tyrannosaurid theropod dinosaur from the cretaceous period 70 to 65 million years ago. It's fossils have been found mainly in Mongolia, although some have been found in China. It is a very large theropod, a fact often overlooked due to it's close and very well known relative Tyrannosaurus is slightly larger. Some regard Tarbosaurus as a synonym of Tyrannosaurus, though this is mainly a minority oppinion.Today, it is widely accepted that the closest relative of Tarbosaurus is another Asian tyrannosaurid, Alioramus, to the point that they are sometimes considered synonymous. Together with Alioramus, Tarbosaurus represents an Asian branch of tyrannosaurines simmilar in many regards to their North American relatives, but different mainly in their stress handling charecteristics of the skull. Tarbosaurus is within the sub-family tyrannosaurinae, along with the North American Tyrannosaurus, Daspletosaurus and possibly Nanotyrannus and the asian Alioramus (though these genra may be a juvenile forms of Tyrannosaurus and Tarbosaurus respetively). Tarbosaurus lived alongside two other very large theropods. However, they would provide little competition for Tarbosaurus. One of them, Therizinosaurus was a herbivore, while the giant ornithomimosaur Deinocheirus was likely an omnivore, taking only small prey. Currently, only one species of Tarbosaurus is recognised, although many have been proposed in the past. The only recognised species today is the type species, T. bataar.
Tarbosaurus is a large theropod. Measuring up to 12m long, and weighing in excess of 5t, it is in the region of size in which many theropods fall into, including its more famous relative Tyrannosaurus. Tarbosaurus posses a bulky body, typical of the very large tyrannosaurines, long legs, short arms and a long and deep tail. It's head is very large, at over 130cm long, the only tyrannosaurid with a larger head is Tyrannosaurus itself. Like most tyrannosaurids, and partiulary tyrannosaurines, it's head was very tall, and had many fused bones for increased strength. However, it's skull was not as wide as that of Tyrannosaurus, meaning it had less potent binocular vision than its North American relative. A unique locking mechanism in its jaw is shared only with Alioramus, and probally helped it with the stresses of hunting armoured prey. Tarbosaurus inhabitted an area were ankylosaurs were common. The unique jaw locking system helped it cope with the stresses of biting such tough prey, it was clearly more aimed at ankylosaur killing than the American tyrannosaurs. As is typical for tyrannosaurids, Tarbosaurus had grealty reduced fore limbs. In fact, Tarbosaurus had the shortest arms relative to its size of any tyrannosaurid known, while Daspletosaurus had the longest. Although no detailed studies have been done on its fore limbs, such studies focused on Tyrannosaurus arms have concluded that with the biceps alone, a Tyrannosaurus was capable of lifting a full 200kg. The tail of Tarbosaurus is fairly typical of a large theropod, accounting for about 50% of the total body length or more, and being quite tall at the base. The large tail would have functioned as a counter balance for the huge head, aswell as provide balance when moving at high speed. Due to the large tail, bulky body, large head and small arms, the centre of gravity for Tarbosaurus was above its hips. Tarbosaurus, as with most tyrannosaurids, had a pair of long legs. The femur to tibia (upper leg bone to lower leg bone) ratio in large tyrannosaurines was around equal, highly unusual for such large theropods. Juvenile animals and albertosaurines had tibias longer than their femur, indicating even higher speed running than adult tyrannosaurines. Based on 'Sue' the Tyrannosaurus, Tarbosaurus probally stood around 3.8m high at the hips, nearly a meter taller than the average bull African Elephant.
Ever since its discovery, Tarbosaurus has always been viewed by some as a junior synonym of Tyrnnosaurus, or at least its cloest relative. This is mainly due to their very simmilar anatomy and size. The main differences sepperating the two animals are features of the skull. Tyrannosaurus had a wider skull, particulary towards the rear, giving it greater binocular vision. The way stress from biting gets disipated across the skull also differs between the two. Tarbosaurus also posses a jaw locking mechanism previously mentioned, which makes the lower jaw more rigid alowing it to handle more stress, while at the same time hindering its opening size. With a skull length of 1.5m, the specimen of Tyrannosaurus nicknamed 'Sue' is estimated to have been able to open its mouth to 100cm wide. If Tarbosaurus had the same capabilities as Tyrannosaurus, it should be able to open its mouth to 90cm. However the previously mentioned jaw locking mechanism will hinder this to some extent. More recently, Alioramus has been viewed as either a juvenile Tarbosaurus, or the closest relative of it. Alioramus also posses the jaw locking mechanism, and shares the charecteristics of how stress is channled through the skull. However, Alioramus posseses significantly more teeth than Tarbosaurus. It was belived that juvenile tyrannosaurs had more teeth than their adults, meaning Nanotyrannus and Alioramus were probably juveniles of Tyrannosaurus and Tarbosaurus respectively. This argument does have a flaw. There are fossils that are definalty juvenile Tarbosaurus, and they have the same muber of teeth as the adults. Alioramus is even excluded from the sub-family tyrannosaurinea altogether by some people, casting further doubt on the theory that it is a juvenile Tarbosaurus. Alioramus also posses a row of small bony crests on its snout that are notably missing from Tarbosaurus.
Several other tyrannosaurids have been synonymised with Tarbosaurus. Shanshanosaurus is probaly a synonym of Aublysodon, and the two are possibly synonymous with Tarbosaurus. It is not clear due to a lack of fossil evidence from Aublysodon. Albertosaurus periculosis, Tyrannosaurus luanchuanensis, Tyrannosaurus turpanensis and Chingkankousaurus fragilis are often considered synonyms of Tarbosaurus.