Tyrannosaurus

Tyrannosaurus was a large theropod dinosaur genus which lived between 68 and 66 million years ago in the Late Cretaceous Laramidia (western part of todays North America). The most well-represented species of the genus was Tyrannosaurus rex, often referred as T-Rex or abbreviated as T. rex. It was one of the latest dinosaurs, and disappeared when the Cretaceous–Paleogene extinction event occurred. Tyrannosaurus is one of the best known and most popular dinosaurs.

Though there were some fossilized tooth and vertebrae found during the late 19th century, the first partial skeleton of T. rex was found by Barnum Brown in Wyoming in 1900, who found two years later the next partial skeleton in the Hell Creek Formation, in Montana. Based on these fossils, Henry Fairfield Osborn described T. rex in 1905^[1]. The meaning of the name Tyrannosaurus rex is "tyrant lizard the king", which refers to the dominance of this dinosaur over the other ones of its time. Until the end of the 1950s, there were no further Tyrannosaurus skeletons found. In the 1960s the interest in T. rex renewed, and 42 further skeletons were discovered. During the 1990s numerous new fossils were found, including the two most complete skeletons, named as Sue and Stan^[2]. These were followed by many new discoveries after 2000^[3][4][5].

Tyrannosaurus rex. By 1Ado123 - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=102690017

Known occurrences of Tyrannosaurus fossils.

Description and anatomy

Tyrannosaurus was a bipedal carnivorous dinosaur with a large, massive skull and a long, heavy and muscular tail. Tyrannosaurus was one of the largest terrestrial predator dinosaurs, and presumably it had the second strongest bite force among all land animals. It had large and powerful hind limbs, and short but strong forelimbs with two digits. The largest found specimen was 13 m long and was estimated to weight about 8.8 tonnes^[6]. The largest skull is about 1.5 m long. The skull of T. rex is wide at the caudal part and narrow anteriorly, which allowed a quite good binocular vision for these predators^[7].

Besides its keen vision, T. rex also was able to sense low frequency sounds, and also had a well developed sense of smell^[8]. Tyrannosaurids had much more powerful bite, than other theropod dinosaurs^[9]. The teeth of Tyrannosaurus were different in their shape. The premaxillary teeth were D-shaped in cross-section, curved backwards, and also had some reinforcing ridges on their back side. The further teeth were more spaced out and robust, banana-shaped, and also having reinforcing ridges. The largest foud T. rex tooth was estimated to be 30.5 cm long including its root^[10].

After finding new tyrannosaurid species in China with feathers^[11], a new study concluded that Tyrannosaurus and other large tyrannosaurids might have been feathered at the upper side of their trunk^[12]. After its description, T. rex was thought to have a posture similar a kangoroo, dragging its tail on the ground. However, based on scientific evidences, it was proved that this was an icorrect position, and in fact, the body of the animal was parallel to the ground, and its tail was extended backwards, balancing the head^[13].

Tyrannosaurus rex. By ABelov2014 - http://abelov2014.deviantart.com/art/Tyrannosaurus-rex-Nanotyrannus-lancensis-577591750, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=61388199

Closely related species

An other, closely related species, Tarbosaurus bataar is known from Mongolia. Originally, it was described as Tyrannosaurus bataar^[14], but later it was renamed^[15]. According to phylogenetic analyses, Tarbosaurus bataar is the sister taxon of T. rex^[16], and some authors have treated it as an Asian Tyrannosaurus species^[17][18].

Paleobiology

Some nearly complete fossilized skeletons of Tyrannosaurus were found, furthermore, at least in one specimen soft tissues and proteins have been preserved. The large number of fossils allowed us to have a better understanding of its biology, biomechanics, life history and physiology. The life-span of Tyrannosaurus was also investigated, it seems that its maximum age might have been around 28 years^[19].

Tyrannosaurus was likely an apex predator of its age, and hunted for probably all kinds of large or medium sized herbivorous dinosaurs. Besides being an active predator, it was also a scavenger. Some researchers suggested that Tyrannosaurus might have been pack hunters, as in South Dakota, there were three skeletons found close to each other^[20], and in northeastern British Columbia, footprints of several specimens heading to the same direction were found^[21]. As the dinosaurs which the T. rex hunted for, like Triceratops and Ankylosaurus, had remarkably effective defenses, it may have been a more succesful startegy for T. rex to cooperate during the hunt with some ther specimens of its kind^[22]. However, this hypothesis was strongly criticised by other experts^[23]. Tyrannosaurus might have had such an infectious bite like today’s Komodo dragon, due to the bacteria living in its saliva^[24].

Tyrannosaurus skeleton. By Agsftw - File:Tyrannosaurus exhibit at the Houston Museum of Natural Science Morian Hall of Paleontology.JPG, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=63404774

Scientific references

[1] Osborn, H. F. (1905): Tyrannosaurus and other Cretaceous carnivorous dinosaurs. Bulletin of the AMNH. 21 (14): 259–265.

[2] Larson, N. L. (2008): One hundred years of Tyrannosaurus rex: the skeletons. In Larson, P.; Carpenter, K. (eds.). Tyrannosaurus rex, The Tyrant King. Bloomington, IN: Indiana University Press. pp. 1–55. ISBN 978-0-253-35087-9.

[3] Currie, P. J.; Hurum, J. H.; Sabath, K. (2003): Skull structure and evolution in tyrannosaurid dinosaurs. Acta Palaeontologica Polonica. 48 (2): 227–234. Retrieved October 8, 2008.

[4] Black, Riley (2015): Tiny terror: Controversial dinosaur species is just an awkward tween Tyrannosaurus. Smithsonian Magazine. Retrieved December 10, 2018.

[5] "Museum unveils world's largest T-rex skull". 2006. Archived from the original on April 14, 2006. Retrieved April 7, 2006.

[6] Persons, S. W.; Currie, P. J.; Erickson, G. M. (2020): An Older and Exceptionally Large Adult Specimen of Tyrannosaurus rex. The Anatomical Record. 303 (4): 656–672. doi:10.1002/ar.24118

[7] Stevens, Kent A. (June 2006): Binocular vision in theropod dinosaurs. Journal of Vertebrate Paleontology. 26 (2): 321–330. doi:10.1671/0272-4634(2006)26[321:BVITD]2.0.CO;2

[8] Erickson, G. M.; Van Kirk, S. D.; Su, J.; Levenston, M. E.; Caler, W. E.; Carter, D. R. (1996): Bite-force estimation for Tyrannosaurus rex from tooth-marked bones". Nature. 382 (6593): 706–708. Bibcode:1996Natur.382..706E. doi:10.1038/382706a0

[9] Witmer, L. M.; Ridgely, R. C. (2009): New Insights into the Brain, Braincase, and Ear Region of Tyrannosaurs (Dinosauria, Theropoda), with Implications for Sensory Organization and Behavior. The Anatomical Record. 292 (9): 1266–1296. doi:10.1002/ar.20983

[10] "Sue's vital statistics". Sue at the Field Museum. Field Museum of Natural History. Archived from the original on September 29, 2007. Retrieved September 15, 2007.

[11] Xing, X.; Norell, M. A.; Kuang, X.; Wang, X.; Zhao, Q.; Jia, C. (October 7, 2004): Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids. Nature. 431 (7009): 680–684. Bibcode:2004Natur.431..680X. doi:10.1038/nature02855

[12] Bell, P. R.; Campione, N. E.; Persons IV, W. S.; Currie, P. J.; Larson, P. L.; Tanke, D. H.; Bakker, R. T. (2017): Tyrannosauroid integument reveals conflicting patterns of gigantism and feather evolution. Biology Letters. 13 (6): 20170092. doi:10.1098/rsbl.2017.0092

[13] Ross, R. M.; Duggan-Haas, D.; Allmon, W. D. (2013): The Posture of Tyrannosaurus rex: Why Do Student Views Lag Behind the Science?. Journal of Geoscience Education. 61 (1): 145–160. Bibcode:2013JGeEd..61..145R. doi:10.5408/11-259.1

[14] Maleev, E. A. (1955) translated by F. J. Alcock: "(title in Russian)" [Gigantic carnivorous dinosaurs of Mongolia]. Doklady Akademii Nauk SSSR (in Russian). 104 (4): 634–637.

[15] Rozhdestvensky, A. K. (1965): Growth changes in Asian dinosaurs and some problems of their taxonomy. Paleontological Journal. 3: 95–109.

[16] Holtz, T. R., Jr. (2004)? Tyrannosauroidea. In Weishampel, D. B.; Dodson, P.; Osmólska, H. (eds.). The dinosauria. Berkeley: University of California Press. pp. 111–136. ISBN 978-0-520-24209-8.

[17] Holtz, T. R. (1994): The Phylogenetic Position of the Tyrannosauridae: Implications for Theropod Systematics. Journal of Paleontology. 68 (5): 1100–1117. doi:10.1017/S0022336000026706

[18] Carr, T. D.; Williamson, T. E.; Schwimmer, D. R. (2005): A New Genus and Species of Tyrannosauroid from the Late Cretaceous (Middle Campanian) Demopolis Formation of Alabama. Journal of Vertebrate Paleontology. 25 (1): 119–143. doi:10.1671/0272-4634(2005)025[0119:ANGASO]2.0.CO;2

[19] Seebacher, F. (2001): A new method to calculate allometric length–mass relationships of dinosaurs. Journal of Vertebrate Paleontology. 21 (1): 51–60. doi:10.1671/0272-4634(2001)021[0051:ANMTCA]2.0.CO;2

[20] Wallis, P. (June 11, 2012): Op-Ed: T. Rex pack hunters? Scary, but likely to be true. Digitaljournal.com. Retrieved December 23, 2015.

[21] McCrea, R. T. (2014): A 'Terror of Tyrannosaurs': The First Trackways of Tyrannosaurids and Evidence of Gregariousness and Pathology in Tyrannosauridae. PLOS ONE. 9 (7): e103613. doi:10.1371/journal.pone.0103613

[22] "Dino Gangs". Discovery Channel. June 22, 2011. Archived from the original on January 19, 2012. Retrieved January 19, 2012.

[23] Switek, B. (July 25, 2011): A bunch of bones doesn't make a gang of bloodthirsty tyrannosaurs. The Guardian. Retrieved June 21, 2015.

[24] Abler, W. L. (1992): The serrated teeth of tyrannosaurid dinosaurs, and biting structures in other animals. Paleobiology. 18 (2): 161–183. doi:10.1017/S0094837300013956