Tarbosaurus: Beast of the Week

This week we will be checking out a huge tyrannosaurid.  Enter Tarbosaurus bataar!  Tarbosaurus was a large meat-eating dinosaur that lived in what is now Mongolia and China during the late Cretaceous Period, about 70 million years ago.  The largest known individuals infer that they could have been just a little smaller than the largest known Tyrannosaurus, at about 39 feet long from snout to tail.  The genus name translates to "Alarming Lizard".  When alive, Tarbosaurus would have shared its habitat with (and maybe hunted) fellow theropods, Deinocheirus and Therizinosaurus, as well as the hadrosaur, Saurolophus.

Tarbosaurus and young...and lunch life (except lunch...lunch is dead) reconstruction by me.

Tarbosaurus was an extremely large tyrannosaurid, second largest known, right behind Tyrannosaurus.  These two genus are very similar in appearance at first glance, but key differences are present.  In fact, the two may not be as closely related to each other as they each might be to other kinds of tyrannosaurids that are known.  Starting at the head, Tarbosaurus had a laterally slim head.  It's eye sockets were primarily facing sideways, so it wouldn't have had much depth perception.  Thanks to scans of the inside of Tarbosaurus' skull, and looking at the shape of the brain case, scientists can infer that Tarbosaurus would have had a great sense of smell and hearing, but it was lacking in the sight department.  It likely would have hunted relying on its sense of smell mostly, unlike T. rex, which had more forward-facing eyes.  Tarbosaurus' teeth were sharp and curved for crushing and tearing flesh and bone, but weren't as proportionally large.  The actual jaws were less flexible than those of most other tyrannosaurids.  It possessed two extremely short arms with two fingers on each hand.  The arms of Tarbosaurus are proportionally the tiniest out of all tyrannosaurids. (Yes, they were even smaller than T. rex's.)  When examined more closely, it was discovered that the arms of Tarbosaurus commonly endured stress factors, meaning they likely weren't completely useless in life.  Some have suggested they aided in taking down prey but personally I feel they may have had some role when it came to mating.  We may never know!

Tarbosaurus skeletal mount on display at the Cosmacaixa Museum in Barcelona, Spain.

There are a relatively large number of Tarbosaurus specimens on the fossil record.  Among these are small juveniles.  Thanks to these individuals, we know that Tarbosaurus was proportionally leggier when it was little, bulking up as it aged.  The teeth were also more blade-like, and less robust when they were young.  Tarbosaurus probably filled different ecological niches as it aged, preying on smaller, faster prey when it was younger, and moving on to bigger game as it matured.  In fact, thanks to bite marks on bones, we can be fairly certain that an adult Tarbosaurus was eating at least Deinocheirus, the giant, flat-billed, ornithomimid.

Juvenile Tarbosaurus skull

Lastly, we have actually found clues as to what Tarbosaurus' skin was like...well at least parts of it.  A large individual had a small patch of skin (sadly we don't know exactly where because it was messed with by fossil poachers) that shows small, round scales.  These scales are each only about two millimeters wide in diameter.  In addition, a Tarbosaurus footprint was discovered, that showed evidence of being scaly as well.  Because of this evidence, many folks tend to argue that Tarbosaurus and its close relatives wouldn't have had feathers in life.  This is flawed, however, since even modern birds possess similar textures on their own feet.  Plus, other fossilized non-avian dinosaurs have been unearthed with evidence of both scales and feathers on other parts of their bodies than the feet.

That is all for this week!  As always feel free to comment below or on the facebook page!

References

Currie, Philip J.; Badamgarav, Demchig; Koppelhus, Eva B. (2003). "The First Late Cretaceous Footprints from the Locality in the Gobi of Mongolia". Ichnos. 10: 1–12.

Hurum, Jørn H.; Sabath, Karol (2003). "Giant theropod dinosaurs from Asia and North America: Skulls of Tarbosaurus bataar and Tyrannosaurus rex compared" (PDF). Acta Palaeontologica Polonica. 48 (2): 161–190.

Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 331-336.

Saveliev, Sergei V.; Alifanov, Vladimir R. (2005). "A new study of the brain of the predatory dinosaur Tarbosaurus bataar (Theropoda, Tyrannosauridae)". Paleontological Journal. 41 (3): 281–289.

Tsuihiji, Takanobu; Watabe, Mahito; Tsogtbaatar, Khishigjav; Tsubamoto, Takehisa; Barsbold, Rinchen; Suzuki, Shigeru; Lee, Andrew H.; Ridgely, Ryan C.; Kawahara, Yasuhiro; Witmer, Lawrence M. (2011-05-01). "Cranial Osteology of a Juvenile Specimen of Tarbosaurus bataar (Theropoda, Tyrannosauridae) from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia". Journal of Vertebrate Paleontology. 31 (3): 497–517.