Nemegt, Gobi Desert, Southern Mongolia
MEANING OF NAME:
When first described, Tarbosaurus bataar was assigned to the North American genus Tyrannosaurus. The differences between these two fossil reptiles are slight and doubtless, the two played much the same ecological role in their communities that is predator or scavenger. Although large, the skull of Tarbosaurus bataar is quite lightweight. This is due to the presence of large air sinuses within the bones, which permitted the skull to be much larger than otherwise possible. This pneumatisation (formation of spaces that are filled with air) in the bones is not restricted to the skull and limb bones, but is seen also in the vertebrae. It is a feature that is common to the saurischian, or lizard-hipped, dinosaurs, a group, which includes the giant sauropods as well as the carnivorous forms. Reduction in size of the arms of Tarbosaurus bataar is not unique to this dinosaur but is common to all the carnosaurs, the large meat-eating dinosaurs. This reduction may have been advantageous in aiding a two-legged animal with a large head to maintain its balance by reducing the weight of its forelimbs. An actual brain of the dinosaur is unknown. The soft brain tissue quickly rotted away after every known dinosaur died. What is preserved in some cases is a natural mould of those parts of the brain where bones of the skull were next to it. In reptiles, the top of the brain rests against the top of the skull but the sides and base of the brain are surrounded by large masses of equally soft tissue that does not fossilize any better than the brain itself. Therefore, only the top of the brain and the pathways of the nerves coming out of the brain where they pass through bony channels in a skull are preserved. This makes it difficult to study dinosaur brains, but even with these limitations, it is fair to say that if a mammal were the size of a Tarbosaurus bataar, one would expect its brain to be 10 times larger than the best estimate that can be made for the size of the one in Tarbosaurus bataar. Tarbosaurus was not a mental heavyweight, to say the least! Predators eat many times their own weight during their lifetime. Therefore, in any balanced natural community over a significant span of time, years or decades, there is a far greater mass of prey species than predators. This being the case, the fact that about one quarter of the bones found in the Nemegt Formation of Mongolia belong to Tarbosaurus bataar implies that the fossil record is not always an accurate reflection of the real numbers of different animals that lived in the area when the rocks in which their remains were found were loose sand in the bed of a river. Rivers tend to selectively preserve certain sizes and shapes of bones, and certainly did so in the case of Tarbosaur bones.
The depression in Tarbosaurus brain case is where the brain rested. The ball on the right is where the skull connected to the vertebral column, the backbone.
Skull PIN 551/1