Tyrannosaur distribution: Laramidia and Asia
Although T. rex is the most popular Tyrannosaur, approximately 9 others ruled at the end cretaceous and were just as fierce. These members of the Tyrannosaur family are only found on the island continent of Laramidia (Western North America) and Asia.
Why Tyrannosaurs are only found in Laramidia and Asia.
It appears Tyrannosaurs originated in North America on the island continent of Laramidia in the late cretaceous.
Since it was an island continent, it was separated from the rest of the world by oceans.
A huge theropod would not have been able to cross oceans to populate other continents.
Laramidia was even too far from South America and Eastern North America (Appalacia) for Tyrannosaurs to migrate to.
This is similar to how Australia is isolated today, and why Australia is full of unique animals.
What about Asia? If Laramidia was an island continent, how did Tyrannosaurs get to Asia? Laramidia (Western North America) and Asia were closer together back then. The pacific was not as wide. Also, at various points in time, it appears there was some kind of land bridge, the bering land bridge, probably between Alaska and Siberia, that connected northern Laramidia to Asia. It is thought that Tyrannosaurs, with many other Laramidia dinosaurs, crossed over to spread throughout Asia.
Now the question becomes, if Tyrannnosaurs could cross to Asia, why couldn't they travel to Europe and Aftica from there?
Europe, at the late cretaceous, was a large group of islands separated by the new Atlantic Ocean. This would have made it difficult for a huge land animal to migrate there. Similarly, South America, Africa and the Australia/Antarctica continents were separated by vast oceans, making it impossible for Tyrannosaurs to migrate there as well.
Only basal groups of Dinosaurs from the Jurassic, when the continents were connected, are found in South America, Africa, and Antarctica/Australa
Map of the late Cretaceous showing the distribution of the Tyrannosaurs.
This is only an approximate late cretaceous map. It was created to show the distribution of Tyrannosaurs. Notice, there are clear gaps in the Tyrannosaur distribution. More types of Tyrannosaurs will probably be found in Asia (Mongolia and China), northern Laramidia (North West U.S. and Canada), and probably even Southern Laramidia (South West U.S.).
The other types of Tyrannosaur dinosaurs:
The Tyrannosaur family belongs to the Ceolurosauria clade. This clade of theropods
is more closely related to birds than other clade of large theropods, the Carnisours
(such as Carcharodontosaurus, and Gigantosaurus). In fact, many of the theropods in
the Ceolurosaur clade have been found to have feathers, includine older relatives of the Tyrannosaur family.
The family of Tyrannosaurus currently contains around 9 genera. There are currently two other unnamed taxon, and more will probably be discovered. The Tyrannosaurus family is characterized by a large and robust skull, foreword facing eyes, and short arms. All of them are also relatively large theropod dinosaurs.
The fossil record shows an incredibly diverse range of Tyrannosaurs. There were over 9 different Tyrannosaurs, each specialized for a specific time period and location.
These dinosaurs were continusouly evolving, getting more specialized. Some grew in size, while others shrunk in size. Some were adapted to the polar regions, while others were adapted to a more tropical climate near the equator. Fortunately for us, Tyrannosaur evolution came to a screeching halt with the end cretaceous mass extinction event.
Click on the Tyrannosaur name below to view more information, or simply scroll down!
This is Figure 4 from Fiorillo AR, Tykoski RS (2014) showing: Phylogenetic positions of Tyrannosauridae. This diagram is used here to show the different genera of Tyrannosaurs, their age ranges and how they are related to one another. Also note the undescribed Tyrannosaur; the "Two Medicine" taxon.
Tyrannosaurs of Laramidia
This is a reconstructed Lythronax argestes on display at the
Natural History Museum of Utah. This photo was released by
the NHMU. Credit: Mark Loewen.
The dinosaur stands 8 feet high at the hips and is 24 feet long.
At 80 million years old, Lythronax argestes is the oldest Tyrannosaur yet discovered. Being found in 2009, it is also one of the most recent Tyrannosaurs to be discovered. The fossils of this beast come from Grand Staircase-Escalante National Monument in Utah, which was located in Southern Laramidia. It was a smaller Tyrannosaur, about 24 feet in length. This Tyrannosaur is intriguing in that paleontologists thought that at 80 million years old, this primitive Tyrannosaur would not have all the features of a more recent Tyrannosaur, like T. rex. However Lythronax was found to still have the short and wide skull, robust teeth, foreword facing eyes, and the typical stubby arms. These Tyrannosaur features must have evolved even earlier than 80 million years ago.
This shows a reconstructed Daspletosaurus specimen FMNH PR308 from
the Dinosaur Park formation of Alberta. It is mounted at the
Field Museum in Chicago.
Image credit: A Stranger in the Alps Via CC3 License.
The next Tyrannosaur to arrive on the scene is Daspletosaurus torosus. This Tyrannosaur was found in 77 to 74 million year old
sediments in the Dinosaur Park formation of Alberta, which was in Northern Laramidia. So far, this is the only older Tyrannosaur
found in Northern Laramidia. The rest are from Southern Laramidia. Daspletosaurus grew to around 30 feet in length. An interesting
characteristic of this Tyrannosaur is that is has crests above its eyes.
There are probably at least two other species of Daspletosaurus Tyrannosaurs. There is another undescribed specimen from the Dinosaur Park formation, and also an undescribed specimen from the Two Medicine Formation in Montana. Once described and published, they will probably be assigned to two other species of Daspletosaurus.
An interesting fact about Daspletosaurus was that it lived alongside another large carnivorous theropod, Gorgosaurus. It is rare to have two large carnivorous theropods in the same area at the same time. There are a couple theories as to why they would be living together. It has been suggested that the two large theropods occupied different ecological niches, where they ate different prey. It has also been suggested that the range of Gorgosaurus was more to the north, while Daspletosaurus was more to the south, and that their ranges in Northern Laramidia did not overlap too much.
This is Figure 3 from Loewn MA, et al (2013) showing: "Skull reconstructions
and selected cranial elements of Teratophoneus curriei" Notice the skull is very short.
Around the same time that Daspletosaurus was living in Northern Laramidia, Teratophoneus curriei was living in Southern Laramidia.
Fossils of Teratophoneus curriei are found in the Kaiparowits formation of south Utah. The formation is around 76 to 74 million years old.
This Tyrannosaur is a smaller, although the specimen found is not an adult, it is only around 20 feet in length. Teratophoneus differs from other Tyrannosaurs of this time in that the skull is shorter and it has less teeth. It may be a more basal form of tyrannosaur (Loewen MA, et al, 2013). The strong differences between this dinosaur and its contemporaries in North Laramidia indicate there may have been a barrier separating North and South Laramidia. The sea may have cut Laramidia in half at some points in time, and the forming Rocky Mountains could have separated the northern and southern fauna.
This is Figure 3 from Loewn MA, et al (2013) showing: "Skeletal reconstructions and postcranial elements of Utah tyrannosaurs".
This shows reconstructions of both (A) Lythronax argestes and (B) Teratophoneus curriei, both found in southern Utah.
This is a comparison of the adult holotype skull (NMMNH P-27469) and
the juvenile skull (P-25049) of the Bistahieversor sealeyi tyrannosaur
dinosaur. Figure from Carr and Williamson, 2010.
Bistahieversor sealeyi lived about 10 million years before T. rex, around 74 million years ago. It is found in the Kirtland formation of New Mexico.
At a length of around 28 feet, it was still smaller than T. rex, but was the top predator of Southern Laramidia at the time.
Bistahieversor is different from other tyrannosaurs in that it had an extra opening above its eye sockets that would accommodate an extra air sack to lighten the skull. It had a keel along the lower jaw, and an extra joint that allowed it's jaws to "lock", similar to Tarbosaurus from Asia.
Cast of "Jane" (BMRP 2--2.4.1) - It may be a
Nanotyrannosaurus lancesis or a juvenile T. rex.
Nanotyranosaurus might be the juvenile form of T. rex. This is currently unclear.
If it is a separate species, this dinosaur, as the name suggests, would be the smallest of the Tyrannosaurs.
Nanotyranosaurus also lived during the same time period of T. rex. However, due to the distinct size different,
it would not have competed with T. rex.
This dinosaur has more teeth than other tyrannosaurs, and is the smallest. Jane is around 21 feet in length. It is also more slender and has longer arms than other tyrannosaurs.
Go to the main T. rex gallery for more information on Nanotyrannosaurus vs Juvenile vs adult T. rex.
Tyrannosaurus rex (T. rex) dinosaurs on display
at the Carnegie Museum of Natural History in Pittsburgh, PA.
Reaching lengths of over 40 feet, the Tyrant Lizard King is the last and the largest of the Tyrannosaurs.
It represents the evolutionary peak of Tyrannosaurs. T. rex died out with the
rest of the dinosaurs during the end Cretaceous mass extinction event.
T. rex lived throughout the island continent of Laramidia. Fossils are found from Alberta down to New Mexico and Texas.
For a complete guide to T. rex, go to the Main T. rex Gallery.
This is figure 3 from: Fiorillo AR, Tykoski RS (2014).
It shows a reconstruction of the Nanuqsaurus hoglundi holotype specimen: DMNH 21461.A.
This specimen includes skull and jaw fragments.
This is the most recent addition to the tyrannosaurs. It is a small polar dinosaur
named after the word "Nanuq" which is an Inupiat (Native Alaskan) name for polar bear.
Skull and Jaw fragments of this dinosaur were found in the Prince Creek formation at the Kikak-Tegoseak Quarry in Northern Alaska. The sediments the fossils came from are dated to be around 69 million years old.
Most Tyrannosaurs are from central and southern Laramidia. Nanuqsaurus, being found in Northern Alaska, is clearly from the polar regions of Laramidia. This is the first arctic tyrannosaur to be found. It was originally thought to be more closely related other theropods, however, a recent study of the holotype skull and jaw fragments by Fiorillo et al. indicate it is closely related to Tyrannosaurus and Tarbosaurus.
Interestingly, this tyrannosaur was a pygmy; about 18 feet, or half the size of an average T. rex. The smaller than usually size of this dinosaur may have been due to adaptations to a harsh arctic environment. Although warmer than today; the arctic in the late Cretaceous was still a colder place than at lower latitudes. It also would have been in darkness for most of the winter. This would make for fewer sources of food. A smaller dinosaur would be better suited than a larger dinosaur in the arctic. A natural land barrier, the Brooks Range, would have isolated this tyrannosaur from the other tyrannosaurs, further contributing to its small size.
The discovery of this pygmy polar tyrannosaur demonstrates the incredible diversity and range of tyrannosaur dinosaurs in the late cretaceous.
Tyrannosaurs of Asia
Tarbosaurus bataar skeleton displayed at the Muzeum Ewolucji PAN w Warszawie.
Image credit: Hiuppo Via CC3 License.
Discovered in the Gobi desert region of Mongolia and China, Tarbosaurus is the T. rex of Asia. It looks very similar to T. rex,
and is even similar in size, around 40 feet. There are small differences between the two. The skull is not as wide and its arms
are even shorter. However, it resembles a T. rex so much that some paleontologists think it may be a sister species in the Tyrannosaurus genus (Tyrannosaurus bataar).
Whatever the case, at the end of the Cretaceous, Tarbosaurus was the apex predator in Asia, while T. rex was the apex predator in Laramidia.
One interesting thing to note is although juvenile T. rex fossils are lacking, there have been juvenile, subadult, and adult specimens of Tarbosaurus found (Tsuihiji T, et al, 2011). These discoveries may help shed light on how T. rex changed from juvenile to adult. A video of the growth seried of Tarbosaurus is shown below:
Video showing the growth series of Tarbosaurus, a closely related dinosaur to T. rex.
Tarbosaurus bataar skeleton displayed at the Muzeum Ewolucji PAN w Warszawie.
This figure shows the lower jaw of Zhuchengtyrannus magnus
Image from: (Hone, et al. 2011).
Zhuchengtyrannus is an older Tyrannosaur from Asia that dates back to 73-74 million years ago.
It was found at the famous Zangjiazhuang quarry in Zhucheng, China. Although it is only known from a few jaw fragments,
(ZCDM V0030 to V0032), Zhuchengtyrannus appears to be a large tyrannosaur, about 39 feet in length.
Not much will be known about this tyrannosaur until new fossils of are discovered in the famous Zangjiazhuang fossil beds.
Tyrannosaurs may have originated from South America in the jurassic when the continents were closer together.
During the late jurassic or early cretaceous, relatives of T. rex moved into Laramidia. These distant relatives were much smaller than the Tyrannosaurs. During this time, a different group of theropods ruled Laramidia, ealry Allosaurs. Tyrannosaur relatives took second place to the allosaurids such as Saits meekerorum. It wasn't until their extinction toward the mid-late cretaceous, could tyrannosaurs take their place as apex predators and grow to their large sizes.
Tyrannosaurus rex, the Tyrant King (Life of the Past)
Peter L. Larson, Kenneth Carpenter (Editors), 2008
This is one of the best Tyrannosaurus rex books out there. It is a collection of everything T. rex, from it's range based on stratigraphy, why it has short arms, to soft tissue reconstruction. It includes many tables, drawings, and photographs. The book also comes with an accompanying CD. The CD has loads of images and animations, including a simulation of the famous T. rex, Stan. This is a wonderful resource for all things T. rex! The book is, however, very technical and not for the casual audience. If you are a T. rex enthusiast, this book is for you.
THE CONCISE DINOSAUR ENCYCLOPEDIA [ Hardcover ]
by Burnie, David. March 2004
This is one of the better general books on dinosaurs. It is incredibly visual and goes over countless dinosaurs lifestyles, behaviors, and the habitat they lived in. It also covers dinsoaur evolution and their extinction.
Carr, T.D.; Williamson, T.E. (2010). "Bistahieversor sealeyi, gen. et sp. nov., a new tyrannosauroid from New Mexico and the origin of deep snouts in Tyrannosauroidea". Journal of Vertebrate Paleontology 30 (1): 1-16. doi:10.1080/02724630903413032.
David W. E. Hone, Kebai Wang, Corwin Sullivan, Xijin Zhao, Shuqing Chen, Dunjin Li, Shuan Ji, Qiang Ji and Xing Xu. (2011). A new, large tyrannosaurine theropod from the Upper Cretaceous of China. Cretaceous Research 32 (4): 495-503. doi:0.1016/j.cretres.2011.03.005.
Farlow, O. James, Brett-Surman, M.K., Editors. (1997) The Complete Dinosaur. IN: Indiana University Press.
Fiorillo AR, Tykoski RS. (2014) A Diminutive New Tyrannosaur from the Top of the World. PLoS ONE 9(3): e91287. doi:10.1371/journal.pone.0091287
Tsuihiji, T., M. Watabe, K. Tsogtbaatar, T. Tsubamoto, R. Barsbold, S. Suzuki, A. H. Lee, R. C. Ridgely, Y. Kawahara, and L. M. Witmer. (2011) Cranial osteology of a juvenile specimen of Tarbosaurus bataar from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia. Journal of Vertebrate Paleontology. 31(3):497-517. PDF here Xu X., Norell, M. A., Kuang, X., Wang X., Zhao Q., & Jia C. (2004) Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids - Nature 431 (7009): 680-684.
Xu, X., Wang, K., Zhang, K., Ma, Q., Xing, L., Sullivan, C., Hu, D., Cheng, S. et al. (2012) A gigantic feathered dinosaur from the Lower Cretaceous of China. Nature 484: 92-95. (.PDF here)