Name:
Tarbosaurus
(Terrifying lizard).
Phonetic: Tar-bo-sore-us.
Named By: Evgeny Maleev - 1955.
Synonyms: Albertosaurus periculosis,
Alectrosaurus periculosus, Aublysodon huoyanshanensis, Aublysodon
lancinator, Aublysodon novojilovi, Chingkankousaurus fragilis,
Deinodon lancinator, Deinodon novojilovi, Deinodon periculosus,
Gorgosaurus lancinator, Gorgosaurus novojilovi, Jenghizkhan
bataar, Jenghizkhan luanchuanensis, Maleevosaurus novojilovi,
Shanshanosaurus huoyanshanensis, Tarbosaurus efremovi, Tarbosaurus
novojilovi, Tyrannosaurus luanchuanensis, Tyrannosaurus
turpanensis, Tyrannosaurus bataar.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Tyrannosauridae, Tyrannosaurinae.
Species: T. bataar (type).
Diet: Carnivore.
Size: 10 to 12 meters body length. Skull up
to and over 1.3 meters long.
Known locations: Mongolia.
Time period: Maastrichtian of the Cretaceous.
Fossil representation: Many specimens (over 30)
together revealing a complete makeup of the skull and post cranial
skeleton.
Classification history and
complications
When
Tarbosaurus fossils were first discovered many of
them were actually
assigned as new species to the existing tyrannosauroid
genera
Tyrannosaurus
(T. bataar) and Gorgosaurus
(G. lancinator
& G. novojilovi), as well as the new
genus and species,
Tarbosaurus efremovi. This classification
continued until 1965
when Anatoly Konstantinovich Rozhdestvensky realised that that all of
these specimens represented the same genus, merely at different
growth stages. All of the other specimens were subsequently included
into the genus as Tarbosaurus with the new type
species being called
T. bataar, but while most palaeontologists
agreed with this some
still referred to the type species as T. efremovi.
This
classification continued without much issue until 1992 when Kenneth
Carpenter examined the fossils and came to the conclusion that most of
the fossils actually belonged within the Tyrannosaurus
genus. The
exception to this was the material that had originally been classed as
Gorgosaurus novojilovi which was placed in its own
genus
Maleevosaurus. However this actually ended up
being synonymised back
into Tarbosaurus in 1999. In 1995 George
Olshevsky created
another name for the Tyrannosaurus bataar material
calling it
Jenghizkhan, as well as recognising previous
genera and species.
After
the end of the twentieth century the vast majority of palaeontologists
only recognised either Tarbosaurus bataar or Tyrannosaurus
bataar as
being legitimate. As time goes on and further study is undertaken,
more and more people are recognising Tarbosaurus
as its own legitimate
genus with key differences being its even smaller arms than those found
in Tyrannosaurus, a different orientation of the
eyes, skull
structure and a lower jaw structure that is different from any
currently known North American tyrannosaur.
Another
Asian tyrannosaur named Alioramus
was also for a long time considered
to
be a synonym to Tarbosaurus. This continued until
the discovery of a
second set of remains which was attributed to a new species of
Alioramus that confirmed Alioramus
as a unique genus totally separate
from Tarbosaurus.
Tarbosaurus as
a living animal
Of
all the currently known tyrannosauroids, Tarbosaurus
was one of the
larger members of the group. Tarbosaurus is also
one of the best
known members with a relatively large amount of fossils attributed to
the genus. It is partly because of this large size that Tarbosaurus
has for a long time been assumed to be synonymous with Tyrannosaurus,
the only other tyrannosaurid currently known to have been larger.
Despite this size similarity there are a few key differences between
these two tyrannosaur genera that are convincing an increasing number
of people into classifying them as separate.
Two
key areas of difference are the tiny arms of Tarbosaurus.
While all
of the later tyrannosauroids are famous for having disproportionately
small arms, Tarbosaurus has arms that are even
smaller than the
rest. The two clawed digits that were Tarbosaurus’s
‘hands’ were
also different to other tyrannosaurs. The second metacarpal is under
half the length of the first metacarpal, something that is the other
way around in other known tyrannosaurid genera.
The
large number of skulls for Tarbosaurus has allowed
for detailed study
into how they worked and different from other tyrannosaurids. Often
in tyrannsoaurids stresses on the bones from the jaws biting down are
transmitted through the maxilla to the nasal bones which have a
reinforced connection to the lacrimal bones via bony struts,
presumably to transmit excess stress to the lacrimal so that the
stress was distributed across a larger area. In Tarbosaurus
these
struts are absent resulting in a weaker connection between the lacrimal
and nasal bones. Tarbosaurus however does have an
enlarged bony
extension from the maxilla that drives into the lacrimal bone
indicating that the stresses from biting forces were passed directly to
the lacrimal bone. The lacrimal also had a more secure fixing to the
prefrontal and frontal skull bones that together made the skull much
more rigid than other tyrannosaurids.
The
rigid construction of Tarbosaurus’s head also
continued to the lower
jaw where a bony ridge that ran down to the dentary which formed what
has been termed a ‘locking mechanism’. This made the lower jaws
very rigid and better able to hold onto powerful struggling prey.
North American contempories at this time lacked the reinforcement and
instead had more flexible lower jaws. This reinforced jaw is however
also seen in Alioramus, and is thought to have
been formed as a
result of a different evolutionary line of tyrannosaurids, or quite
possibly to deal with different types of prey.
Skull
study has also allowed for reconstructions of Tarbosaurus’s
brain to
made, something that led to the discovery that it was very similar to
other tyrannosaurids. As such Tarbosaurus had a
brain that was more
like that of a crocodile than that of a bird. The most developed
areas of the brain were the areas associated with smell. These were
extremely well developed and there was also the presence of a
vomeronasal organ, something that would have helped it to detect
pheromones. This means that the sense of smell was very important to
Tarbosaurus, and it may have needed to use smell
to track others of
its kind when looking for a mate.
Tarbosaurus
also had well developed hearing that suggests members of its species
may have called out to one another, either to establish territorial
boundaries or to attract potential mates into their areas.
Tarbosaurus also seems to have had a well-developed
sense of balance,
something that may have helped it greatly as the sideward position of
the eyes suggest that it may have had to turn its head to one side so
that it could look forward to clearly see where it was walking.
The
visual centres of the brain however are actually quite underdeveloped,
and one key reason for this could be the shape of the skull. Because
the back of Tarbosaurus’s skull is quite narrow,
the eyes looked out
more to the sides rather than directly ahead. This means that
Tarbosaurus did not have the sharp stereoscopic
vision that other
tyrannosaurids had, and aside from potentially having a blind spot in
front of its snout, it would not have been able to gauge distances as
effectively as other tyrannosaurids. This may not have been a
critical flaw however as if Tarbosaurus had a
preference for hunting
larger and slower prey animals, it would not have had such a great
reliance upon vision.
Tarbosaurus
hunting and possible
prey specialisation
The
highly developed sense of smell combined with the underdeveloped sight
can be used to draw the easy conclusion that Tarbosaurus
was adapted
more for scavenging than active hunting. However such a quick
conclusion may not be the correct one when you look at the fossils of
the rest of the animal as well as potential prey items. Dinosaurs,
particularly predatory ones, are always studied for signs of stress
fractures, injuries and damage caused by repeated actions throughout
the animal’s life. The key area for stress fractures in Tarbosaurus
was surprisingly found in the hands, an area that could not be in
contact with the ground. The most plausible explanation for the
presence of an injury caused by repeated behaviour would be contact
with another large dinosaur, another of its own kind or perhaps a
large prey item.
Tarbosaurus
also did not have the acute stereoscopic (binocular) vision
associated with its North American cousins. Some possible prey items
were large hadrosaurs like Saurolophus, but there
were also
titanosaurid sauropods
such as Nemegtosaurus.
These large dinosaurs
would not require exceptional vision to find and hunt and would have
quite possibly been slow on their feet making them viable prey for
capture. Their size however would require Tarbosaurus
to get close
and physical to make a kill, a possible explanation for the stress
fracture to the hand.
Many
of the other dinosaurs in the region would have been smaller and often
swifter than Tarbosaurus, meaning that it would
have been restricted
to the larger dinosaurs that other smaller tyrannosauroids like
Alioramus were better adapted to catch. Whereas
the potential is
there for Tarbosaurus to have been an active
hunter, it may still
have had a greater tendency to turn to scavenging to augment its diet
than others of its group. It may have even used its sheer size and
bulk to intimidate other smaller predators into giving up their kills,
behaviour that can be observed in carnivores that are still active
predators today.
Further reading
- New carnivorous dinosaurs from the Upper Cretaceous of Mongolia. -
Doklady Akademii Nauk SSSR 104 (5): 779–783. - Evgeny A. Maleev - 1955.
- Giant carnivorous dinosaurs of Mongolia - Doklady Akademii Nauk SSSR
104 (4): 634–637. - Evgeny A. Maleev - 1955.
- Growth changes in Asian dinosaurs and some problems of their taxonomy
- Paleontological Journal 3: 95–109. - Anatoly K. Rozhdestvensky - 1965.
- Gigantic carnosaurs of the family Tyrannosauridae - The Joint
Soviet-Mongolian Paleontological Expedition Transactions 1: 132–191. -
Evgeny A. Maleev - 1974.
- A new Late Cretaceous carnosaur from Nogon−Tsav, Mongolia - The Joint
Soviet-Mongolian Paleontological Expedition Transactions (in Russian)
3: 93–104 - Sergei M. Kurzanov - 1976.
- Carnivorous dinosaurs from the Cretaceous of Mongolia - The Joint
Soviet-Mongolian Paleontological Expedition Transactions 19: 5–119. -
Rinchen Barsbold - 1983.
- Late Mesozoic stratigraphy and vertebrates of the Gobi Basin -
Cretaceous Research 12 (4): 345–377 - Tomasz Jerzykiewicz &
Dale A.
Russell - 1991.
- New information on Shanshanosaurus huoyanshanensis,
a juvenile
tyrannosaurid (Theropoda, Dinosauria) from the Late Cretaceous of China
- Canadian Journal of Earth Sciences 38 (12): 1729–1737. - Philip J
Currie, & Dong Zhiming - 2001.
- Skull structure and evolution in tyrannosaurid phylogeny, Acta
Palaeontologica Polonica 48 (2): 227–234. - Philip J. Currie, J�rn H
Hurum & Karol Sabath - 2003.
- Giant theropod dinosaurs from Asia and North America: Skulls of
Tarbosaurus bataar and Tyrannosaurus rex
compared - Acta
Palaeontologica Polonica 48 (2): 161–190. - J�rn H. Hurum &
Karol
Sabath - 2003.
- A new study of the brain of the predatory dinosaur Tarbosaurus
bataar
(Theropoda, Tyrannosauridae) - Paleontological Journal 41 (3): 281–289
- Sergei V. Saveliev & Vladimir R. Alifanov - 2005.
- 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. - Takanobu Tsuihiji, Mahito Watabe,
Khishigjav Tsogtbaatar, Takehisa Tsubamoto, Rinchen Barsbold, Shigeru
Suzuki, Andrew H. Lee, Ryan C. Ridgely, Yasuhiro Kawahara &
Lawrence M. Witmer - 2011.
- Tyrannosaur feeding traces on Deinocheirus
(Theropoda:?Ornithomimosauria) remains from the Nemegt Formation (Late
Cretaceous), Mongolia. - Cretaceous Research. 37: 186–190. - P. R.
Bell, P. J. Currie & Y. N. Lee - 2012.
- Diet preferences and climate inferred from oxygen and carbon isotopes
of tooth enamel of Tarbosaurus bataar (Nemegt Formation, Upper
Cretaceous, Mongolia). - Palaeogeography, Palaeoclimatology,
Palaeoecology. 537: 109190. - Krzysztof Owocki, Barbara Kremer, Martin
Cotte & Herv� Bocherens - 2020.