Tyrannosaurus is a genus of coelurosaurian dinosaur. Tyrannosaurus is known from more than 40 specimens and is the most well represented species of Dinosaur. Tyrannosaurus lived in North America during the Late Cretaceous approximately 68-66 million years ago.

Tyrannosaurus was one of the last non-avian dinosaurs before the K-PG mass extinction event. Tyrannosaurus was a large bipedal theropod tyrannosaurid dinosaur with a large head, and large jaws.


The jaw of Tyrannosaurus could bite down with almost 12,800 pounds. Such a force was used to crush bone, and inflict massive damage to its prey. Tyrannosaurus is theorized to have been a solitary animal, although the opposed is theorized by other Scientists. Tyrannosaurus had a large, muscular tail used for balancing, as well as large powerful legs. Despite Tyrannosaurus' large size, it's arms are 3 feet long and when compared to its body; are tiny. Tyrannosaurus' arms are estimated to have been able to curl about 430 pounds. The Tyrannosaurus' speed is unknown; however recent research has shown the theropod to be rather slow and to be unable to run. [1][2]

Only one specimen, 'B-rex', is the only fossil documented with having sexual dimorphism. The specimen was preserved with soft tissue, that can tell us it was a female. The soft tissue showed that 'B-rex' was ovulating. Several specimens have wider pelvis' and modified tail bones, which may have helped in the passage of eggs.


Over 30 specimens of Tyrannosaurus have been discovered, most found in North America, and several others found in Asia. Here is a list of all known locations Tyrannosaurus remains have been found in:

  • Montana
  • Texas
  • Utah
  • Wyoming
  • Alberta
  • Saskatchewan
  • Mongolia
  • New Mexico (footprint, undisclosed)


Stan skeletal

Skeletal System

All Tyrannosaurus fossils are incomplete so no one knows how many bones an adult Tyrannosaurus had. One of the biggest specimen of Tyrannosaurus was 'Sue' (now dwarfed by another specimen, 'Stan') discovered and named after Susan Hendrickson near Faith, South Dakota, in August 1990. 'Sue' has since been dwarfed by a specimen discovered in 1987 named by and discovered by Stan Sacrison (also discovered a specimen named 'Duffy'.) The team recovered 199 bones and is now on display at the Black Hills Institute of Geological Research.

Tyrannosaurus had a massive skull, which was supported by a thick S-shaped neck. The vertebrae are very thick like all large-bodied dinosaurs. Compared to the rest of the body, the forelimbs of Tyrannosaurus were tiny, being only 1 meter long in comparison to their 12-13 meter total body length. The legs were built strongly built, and supported the large body weight with three played toes. Like all theropod dinosaurs, the fourth toe, dubbed the hallux, was considerably shortened, did not reach the ground, and pointed backwards on the ankles. The heavy organs were supported by a second set of ribs called gastralia, which are located on the underside of the chest

Musculoskeletal System

Rex muscle

T. rex musculature Credit: R.J. Palmer

The muscular system in Tyrannosaurus was extremely strong and developed compared to other dinosaurs. The tail, legs, arms and neck were covered in thick muscle tissue to help the animal move properly in life. The large thick muscles on the neck were used to move the neck and to support the large weight produced by the skull. The thighs, calves and biceps on the arms and legs were exceptionally strong. The exact use for the miniature arms remains unknown, but it is thought that Tyrannosaurus either used them as anchors whilst mating, an aid to stand up, or for toppling and grabbing prey while the animal delivered the killing bite.

Disease and Injuries

Trichomonosis rex jaw

Trichomonosis as seen in Sue. Credit: Everything Dinosaur Blog

The world-renowned specimen, Sue, is one of the most consistent Tyrannosaurs to show disease and injury. While studying the specimen, scientists noticed many injuries. Sue had began to develop arthritis in the caudal vertebrae located in the tail. This disease was likely caused by age. Sue was about 28 years old when they died, which is why the joints in its tail began to swell, causing arthritis. Other pathologies recorded in Sue's skeleton include healed fractures on the ribs, broken legs which had became infected and healed, gashes in the vertebrae caused by other tyrannosaurids and unnatural holes in the mandible. Scientists speculate that the strange holes in the lower jaw would have made normal feeding techniques extremely painful, and may have been the cause of death. Similar holes torn into the lower jaws of tyrannosaurids have been observed in Daspletosaurus and some modern bird species today, caused by an infectious disease named trichomonosis.


According to the Field Museum, the teeth of Tyrannosaurus would have carried loose chunks of flesh in life. This would have caused the mouth to have reeked. The study was conducted to be part of an attraction in Sue the Tyrannosaurus' suite in the Field Museum, were visitors can smell Sue's breath and touch its skin.


In 1902 Tyrannosaurus was discovered by Barnum Brown, and named in 1905 by Henry Fairfield Osborn. That same year, Barnum named another theropod Dinosaur, calling it Dynamosaurus. Dynamosaurus was made a synonym of Tyrannosaurus shortly after he realized they were the same animal. In 2020, a paper was released confirming that Nanotyrannus was in fact, a synonym of Tyrannosaurus, proving Jack Horners suspicions about the genus. [Paper here]

Genus Synonymy

Species Synonymy

Life History


Credit: R.J. Palmer


Tyrannosaurus underwent a vast array of ontogenic advancements throughout their lives. Juvenile specimens often are misunderstood as the dubious genus Nanotyrannus. Tyrannosaurus started off small, and through their teenage years, underwent a serious of massive growth spurts. They gained about 400 pounds per year, which became a massive body size, strong musculature and overall ability to keep the body running. The graph and chart show the growth cycle of Tyrannosaurs, and tyrannosaurids in general.

Notable Specimens

FMNH PR2081 'Sue' : One of the most famous specimens know, 'Sue' (named after Susan Hendrickson, who discovered the skeleton). Sue is 98% complete and 41 feet long. Sue had many healed injuries, holes in the bones, and was 28 years old when they died.

RSM P2523.8 'Scotty' : Discovered in Saskatchewan, Canada in 1991, 'Scotty' was named after the bottle of scotch the excavation team celebrated with. Scotty is 8.8 pounds, out sizing Sue. Scotty was 70% complete upon description.

MOR 1125 'B-Rex' : Discovered by Dr. Jack Horner, this specimen preserved soft tissue, which shows that dinosaurs had a birth cycle like that of birds.

BHI 3033 'Stan' : Discovered in South Dakota in 1987, named after Stan Sacrinson, 'Stan' is now the largest Tyrannosaurus known. Stan is 70% complete and was described at the Black Hills Institute.








Two Medicine Formation tyrannosaur








The Tyrannosaurus probably used closed mouth vocalization, a trait used in crocodiles. Tyrannosaurus may have made loud, deep bellowing sounds, which would had felt like intense vibrations. The sound would have been a nearly inaudible booming sound, which would have rumbled through the dense arid forests in Late Cretaceous Montana. Instead of exhaling to make the sound, the sound is made in birds by sucking in air while their beaks are closed. The sound releases as a deep rumbling sound, while the jaws still remain closed. Other animals would have barely been able to hear the noise, but would have been able to feel it.

Saurian Tyrannosaurus Audio Demonstration (
Final 5f23414f495f23001373b9ec 82259 (


Versus triceratops

Credit: R.J. Palmer

Tyrannosaurus lived in the Hell Creek Formation during the Late Cretaceous. It was the apex predator in its ecosystem. Tyrannosaurus was likely featherless, due to the arid climate of Cretaceous Montana. Tyrannosaurus preyed on Triceratops and Edmontosaurus, and was a fellow predator alongside Dakotaraptor and Acheroraptor.


Life Reconstructions

Fossils and Skeletons


  • According to the Field Museum, of which Sue is kept at, Sue prefers the they/them pronouns. They further specify that scientists have yet to figure out Sue's gender. When first studied, scientists though Sue as a she, later recalling the statement.
  • In the Field Museum, Sue the Tyrannosaurus has its own "suite". Featured attractions are a cast of Sue's mostly complete skeleton, stations where people can touch Sue's skin, here its sounds, and smell its breath. Alongside the skeleton is a separate display case for its gastralia and a realistic life sized model (see first image in gallery) holding an Edmontosaurus nicknamed "fleshy" in its jaws.


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