Tyrannosaurus (meaning “tyrant lizard”, from the Ancient Greek tyrannos (τύραννος), “tyrant”, and sauros (σαῦρος), “lizard”) is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex (rex meaning “king” in Latin), is one of the most well-represented of the large theropods. Tyrannosaurus lived throughout what is now western North America, on what was then an island continent known as Laramidia. Tyrannosaurus had a much wider range than other tyrannosaurids. Fossils are found in a variety of rock formations dating to the Maastrichtian age of the upper Cretaceous Period, 68 to 66 million years ago. It was the last known member of the tyrannosaurids, and among the last non-avian dinosaurs to exist before the Cretaceous–Paleogene extinction.
Fortunately, dinosaurs existed on Earth long before the arrival of man, and more specifically for the Rex species, the period is located about 65 million years ago during the Cretaceous era. In our days, the evidences of this magnificent animal come to us through fossil remains (30 of them found with an almost complete skeleton), mainly found in regions of North America such as Colorado (1874) and Wyoming (1890).
In 1905, the American paleontologist Henry Fairfield Osborn would manage to gather all the existing information until then to prepare a complete report on the Tyrannosaurus Rex (name given by the researcher himself), and whose impressive characteristics the entertainment industry has used to promote admiration and interest in one of the most popular animals that inhabited our planet.
Size (in green) compared with selected giant theropods. Author: Matt Martyniuk. Size comparison of selected giant theropod dinosaurs and a human. Adapted from or matching illustrations and measurements published by the following authors: Spinosaurus after proportions and measurements in N. Ibrahim et al. (2014) “Semiaquatic adaptations in a giant predatory dinosaur” (silhouette adapted from image by ArthurWeasley), Carcharodontosaurus, Giganotosaurus, and Tyrannosaurus matching measurements and diagrams by G. S. Paul (2010) “The Princeton Field Guide to Dinosaurs”, pp. 97, 98, 108, 109, and Scott Hartman. Tyrannosaurus rex has been known to science since the end of the nineteenth century, and to this day remains arguably the most popular dinosaur the world over. This is evidenced by its almost mandatory inclusion in books, TV shows, games and websites that are about dinosaurs in general. Tyrannosaurus also probably has more toys and merchandising relating to it than any other dinosaur.
Illustration of the tyrannosaurid Tyrannosaurus rex with minimal feathers based on phylogenetic bracketing. Author: Durbed
Like other tyrannosaurids, Tyrannosaurus was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to its large and powerful hind limbs, Tyrannosaurus fore limbs were short but unusually powerful for their size and had two clawed digits. The most complete specimen measures up to 12.3 m (40 ft) in length, up to 3.66 meters (12 ft) tall at the hips, and according to most modern estimates 8.4 metric tons (9.3 short tons) to 18.5 metric tons (20.4 short tons) in weight. Although other theropods rivaled or exceeded Tyrannosaurus rex in size, it is still among the largest known land predators and is estimated to have exerted the largest bite force among all terrestrial animals. By far the largest carnivore in its environment, Tyrannosaurus rex was most likely an apex predator, preying upon hadrosaurs, armoured herbivores like ceratopsians and ankylosaurs, and possibly sauropods. Some experts, however, have suggested the dinosaur was primarily a scavenger. The question of whether Tyrannosaurus was an apex predator or a pure scavenger was among the longest ongoing debates in paleontology. It is accepted now that Tyrannosaurus rex acted as a predator, and opportunistically scavenged as modern mammalian and avian predators do.
Tyrannosaurus specimen AMNH 5027 at the American Museum of Natural History.
T. rex‘s serrated, conical teeth were most likely used to pierce and grip flesh, which it then ripped away with its brawny neck muscles. Its two-fingered forearms could probably seize prey, but they were too short to reach its mouth.
Scientists believe this powerful predator could eat up to 500 pounds (230 kilograms) of meat in one bite. Fossils of T. rexprey, including Triceratops and Edmontosaurus, suggest T. rex crushed and broke bones as it ate, and broken bones have been found in its dung.
Predator or Scavenger? One of the most controversial theories about Tyrannosaurus is if it was actually a predator at all, but instead lived the life of a scavenger. Some have said that its size, even when combined with lower weight estimates meant that it could not run, as in both feet off the ground at the same time. Biomechanical studies have also shown that it was no way near as fast as it is sometimes depicted in movies. It is popularly said that for a Tyrannosaurus to run at 25 miles per hour, it would need up to of around 80% of its muscle mass in its legs, an unheard of scenario. What are considered more realistic estimates place top speed at around the 11 miles per hour mark. A slower than expected speed does not mean that Tyrannosaurus was a scavenger however. You have to remember that predators need to be only fast enough to catch their prey.
Under an entirely carnivorous regime (although it has been proven that it also fed on carrion), the Tyrannosaurus Rex has been listed as one of the most effective and voracious predators in the animal world. Their usual menu was made up of species such as Ceratopsids and Hadrosáuridos.
Like all great hunters of nature, the Tyrannosaurus possessed excellent qualities in this regard, such as its powerful jaws, capable of reaching a meter and a half in length, as well as its sharp and curved teeth (slightly inclined backwards to grasp the meat more easily), and about 20 centimeters in size for each piece, which together meant a pressure force of almost four tons in each bite.
Tyranossaurus rex menu by PrehistoricWildlife.com Tyrannosaurus rex was one of the largest land carnivores of all time; the largest complete specimen, located at the Field Museum of Natural History under the name FMNH PR2081 and nicknamed Sue, measured 12.3 meters (40 ft) long, and was 3.66 meters (12 ft) tall at the hips, and according to the most recent studies estimated to have weighed between 8.4 metric tons (9.3 short tons) to 18.5 metric tons (20.4 short tons) when alive. However, not every adult Tyrannosaurus specimen recovered is as big. Historically average adult mass estimates have varied widely over the years, from as low as 4.5 metric tons (5.0 short tons), to more than 7.2 metric tons (7.9 short tons), with most modern estimates ranging between 5.4 metric tons (6.0 short tons) and 8.0 metric tons (8.8 short tons). Hutchinson et al. (2011) found that the maximum weight of Sue, the largest complete Tyrannosaurus specimen, was between 9.5 and 18.5 metric tons (9.3–18.2 long tons; 10.5–20.4 short tons), though the authors stated that their upper and lower estimates were based on models with wide error bars and that they “consider [them] to be too skinny, too fat, or too disproportionate” and provided a mean estimate at 13.99 metric tons (15.42 short tons) for this specimen.
Scale chart for various specimens of Tyrannosaurus rex. Relative sizes based on skeletal drawings by Scott Hartman. Silhouettes adapted from original drawings by Matt Martyniuk. Author: Matt Martyniuk
Skin and feathersFull size model in Poland, depicting Tyrannosaurus with both feathers and scales, and with lipped jaws.
While there is no direct evidence for Tyrannosaurus rex having had feathers, many scientists now consider it likely that T. rexhad feathers on at least parts of its body, due to their presence in related species. Mark Norell of the American Museum of Natural History summarized the balance of evidence by stating that: “we have as much evidence that T. rex was feathered, at least during some stage of its life, as we do that australopithecines like Lucy had hair.”The jaws of Tyrannosaurus were tremendously powerful with a bite force of larger individuals being measured in several tons. The teeth were primarily arranged into biting incisors at the front, with larger canines to the size and rear of the mouth. The incisors that are on the premaxilla form a ‘D shaped’ curve around the front, which is notable as this gave Tyrannosaurus (and others of its group) a ‘U shaped’ snout. Other well-known carnivorous theropods such as Allosaurus were more ‘V shaped’. The ‘U’ shaped snout means that Tyrannosaurus had more ‘pick-up’ every time it took a bite than other dinosaurs. The teeth towards the sides of the mouth were the most suited to crushing, and grow anywhere up to 30 centimetres long when including the root. The teeth of the lower jaw (mandible) were smaller than those above, and fitted inside the upper jaw so that when closed, only the upper teeth would protrude out and downwards.
Close up of “Sue” T-Rex replica skull at the Field Museum of Natural History in Chicago, IL. Author: Scott Robert Anselmo
T. rex fossils are found in a variety of rock formations dating to the Maastrichtian age of the upper Cretaceous period, which lasted from 67 million to 65 million years ago, toward the end of the Mesozoic Era. It was among the last of the non-avian dinosaurs to exist prior to the Cretaceous-Paleogene extinction event, which wiped out the dinosaurs.
More mobile than many other land-based dinosaurs, T. rex roamed throughout what is now western North America, at the time an island continent identified as Laramidia. More than 50 skeletons of T. rex have been unearthed, according to National Geographic. Some of these remains are nearly complete skeletons, and at least one skeleton included soft tissue and proteins.
Tyrannosaurus and other animals of the Hell Creek Formation
Tyrannosaurus lived during what is referred to as the Lancian faunal stage (Maastrichtian age) at the end of the Late Cretaceous. Tyrannosaurus ranged from Canada in the north to at least Texas and New Mexico in the south of Laramidia. During this time Triceratops was the major herbivore in the northern portion of its range, while the titanosaurian sauropod Alamosaurus “dominated” its southern range. Tyrannosaurus remains have been discovered in different ecosystems, including inland and coastal subtropical, and semi-arid plains.
Several notable Tyrannosaurus remains have been found in the Hell Creek Formation. During the Maastrichtian this area was subtropical, with a warm and humid climate. The flora consisted mostly of angiosperms, but also included trees like dawn redwood (Metasequoia) and Araucaria. Tyrannosaurus shared this ecosystem with Triceratops, related ceratopsians Nedoceratops, Tatankaceratops and Torosaurus, the hadrosaurid Edmontosaurus annectens and possibly a species of Parasaurolophus, the armored dinosaurs Denversaurus, Edmontonia and Ankylosaurus, the dome headed dinosaurs Pachycephalosaurus, Stygimoloch, Sphaerotholus, and Dracorex, the hypsilophodont Thescelosaurus, and the theropods Ornithomimus, Struthiomimus, Orcomimus, Acheroraptor, Dakotaraptor, Richardoestesia, Paronychodon, Pectinodon and Troodon.
Hell Creek dinosaurs and pterosaurs by durbed on Deviantart. Various dinosaurs and pterosaurs from the Hell Creek Formation. From back to front: Ankylosaurus, Tyrannosaurus, Quetzalcoatlus, Triceratops, Struthiomimus, Pachycephalosaurus, and the unnamed dromaeosaurid and caenagnathid now named Acheroraptor and Anzu respectively. Author: Durbed