Tarbosaurus

Phylogeny: Dinosauria > Saurischia > Theropoda > Neotheropoda > Tetanurae > Avetheropoda > Coelurosauria > Tyrannosauroidea > Pantyrannosauria > Eutyrannosauria > Tyrannosauridae > Tyrannosaurinae > Tyrannosaurini

Overview: There are some researchers who see this animal as an Asian species of Tyrannosaurus – Tyrannosaurus bataar. In 1955, when its fossils were described by the Soviet paleontologist Evgeny A. Maleev, it was classified as such. Remains of the creature were found a few years earlier in the Gobi Desert of Mongolia by Soviet and Mongolian fossil hunters. Maleev would also describe fossil material of a slightly smaller tyrannosaur, which he referred to a new genus called Tarbosaurus in the same year. Studies in the 1960’s would conclude the latter was actually just a younger growth stage of the former, finding them to be the same animal. This same study would find a number of differences between said animal and Tyrannosaurus, enough to be distinct genera. From that time onward, Tarbosaurus would become the preferred name for said genus. Some studies do still find Tarbosaurus to be a junior synonym of Tyrannosaurus, but most treat the two as separate. Both, however, belonged to the family Tyrannosauridae. Tarbosaurus and Tyrannosaurus were among each other’s closest relatives, within the subfamily Tyrannosaurinae and tribe Tyrannosaurini.

Superficially, most would notice few differences between Tarbosaurus and Tyrannosaurus, but on a more detailed level, they do become apparent. Skull differences between the two genera are quite notable, at least when viewed from above. While both had enormous skulls, that of Tyrannosaurus had a wider profile, especially at the back, giving it more forward-facing vision (and therefore good depth perception). Tarbosaurus had a narrower skull overall, so its eyes pointed out more towards the sides, which was fairly common among theropods. Studies reveal the jaws of the more famous North American genus were suited for stronger, bone-crushing forces, though it seems to have had fewer teeth than Tarbosaurus. Setting aside their skulls, there were other key features setting the two apart, including arm length. All tyrannosaurids had short arms, but those seen on Tarbosaurus were proportionately the shortest of the family, though all of them had only two clawed digits. Both were enormous theropods, but Tarbosaurus was usually more lightly built and averaged a meter or two shorter in terms of length, measuring ten to twelve meters long as an adult.

Paleontologists tend to point to differences in their respective hunting niches and available prey to explain all of these anatomical contrasts. Tyrannosaurus mainly hunted large hadrosaurs, armored ankylosaurs, and powerful ceratopsids like Triceratops. Tarbosaurus, on the other hand, appears to have preyed on titanosaurian sauropods like Nemegtosaurus. In this way, its prey was more similar to that of the earlier Allosaurus, so having a similarly less powerful bite and narrower skull makes a bit of sense. Instead of delivering bone-crushing bites, Tarbosaurus would strip away large chunks of flesh from its sauropod prey. Fossils of both Tarbosaurus and Nemegtosaurus are mainly known in Mongolia’s Nemegt Formation, which preserves a vast floodplain featuring twisting rivers, marshes, and dense forests. Other dinosaurs from the Nemegt would include Therizinosaurus, Deinocheirus, Gallimimus, Zanabazar, Alioramus, Saurolophus, Tarchia, and Prenocephale. Fossils likely belonging to Tarbosaurus are also known from the Subashi Formation in western China. In both localities, it’s highly probable that Tarbosaurus was by far the largest carnivore and predator present.