Tyrannosaurus

## Tyrannosaurus rexTyrant Lizard King

* Male
* Female
* Subadult Males
* Juvenile

* **Eyeball Diameter** of 14 centimeters (5.5 inches)
* **Skull Length** of 1.5 meters (5 feet)
* **Skull Weight** of 272 kilograms (600 pounds)
* **Bite Force** of 5 - 6.1 tons (10,000 - 12,100 pounds)
* **Tooth Length** of 30 centimeters (12 inches) (crown and root each take up half of the tooth)
* **Maximum Jaw Gape** of 80 degrees
* **Bicep Lifting Strength** of 200 kilograms (441 pounds)
* **Walking Speed** of 1.28 meters per second, or 4.6 kilometers (3 miles) per hour
* **Top Speed** of 27 kilometers (17 miles) per hour
* **Life Expectancy** of around 24 - 30 years

 **Main** Segments Gallery

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***“ T. rex. The most powerful land predators on the planet. ”***

― **David Attenborough**, *Swamps*
***Tyrannosaurus rex*** (Tyrant Lizard King) is a genus of tyrannosaurid theropod dinosaur that served as the apex predator of western North America, 68 - 66 million years ago, during the Maastrichtian stage of the Late Cretaceous Period. Often referred to as the king of the dinosaurs, it is arguably the most well-known dinosaur to have ever walked the Earth.

## Paleobiology

### Size and Physique

*Tyrannosaurus rex* is the last, largest, and most heavily-built of the tyrannosaurs, a group of massive predators that dominated their respective ecosystems during the Late Cretaceous Period. Previous calculations regarding the size of *Tyrannosaurus rex* estimated lengths of up to 14 meters (46 feet), but these measurements are now considered outdated overestimates in the light of more recent studies, which estimate an average of 3.66 - 4 meters (12 - 13 feet) in height, 12.3 - 12.4 meters (40 - 41 feet) in length, and 7 - 8 metric tons (7.7 - 8.8 short tons) in weight. The largest known *Tyrannosaurus* is specimen RSM P2523.8 (nicknamed "Scotty" after the celebratory bottle of scotch shared by the team that discovered the specimen), which achieved a length of 13 meters (43 feet) and a mass of almost 9 metric tons (10 short tons), though it should be noted that "Scotty" is an exceptionally-large individual, and most *T. rexes* likely didn't grow that big. While evidence suggests that "Scotty" is actually one of the youngest and least mature of the adult *T. rexes* found so far, thus implying a greater potential maximum growth size for the species, this does not explain how older *T. rex* specimens, like 28 year-old FMNH PR 2081 (nicknamed "Sue" after American explorer and fossil collector Sue Hendrickson, who discovered the specimen in South Dakota on August 12, 1990), were smaller than him. This suggests that "Scotty" gained its exceptional size not due to age, but due to genetic factors, an abundance in resources, ideal environmental conditions, or a combination of these various factors.

***“ Deinocheirus. It's even taller than T. rex, and its massive duck-billed snout is very effective in gathering water plants. ”***

― **David Attenborough**, *Freshwater*
Oftentimes, *T. rex* is used as a standard by which other theropods are measured. Prehistoric Planet itself does this, with *Deinocheirus* (possessing a height of 4.4 meters, or 14 feet) being introduced in the Freshwater episode as "even taller than *T. rex*". While not the longest or tallest theropod, in terms of body mass, *Tyrannosaurus rex* is the heaviest known theropod, and is thus seen as the most powerful, a view that stands more than a hundred years after its remains were first discovered.

In 2022, a paper by Gregory S. Paul brings up the theory that there may be three *Tyrannosaurus* species (*T. rex*, *T. regina*, and *T. imperator*) instead of just one based on size and morphological differences between various specimens (the idea being that the robustness of some specimens cannot simply be attributed to individual variation). While this theory has not seen widespread support (with other paleontologists like Dr. Thomas D. Carr and Dr. Lindsay Zanno considering the work unconvincing and lacking in validity), it does bring up specimen BHI 6248 (nicknamed "E.D. Cope", named after renowned American paleontologist Edward Drinker Cope), a *T. rex* fossil discovered in June 2000, possessing a femur circumference of 63 centimeters (25 inches), which exceeds even those of "Scotty" (59 centimeters, or 23.23 inches). Additionally, there is another large *T. rex* specimen nicknamed "Bertha". The specimen, unearthed in North Dakota in the 1990s, is only known from three bones (a tibia, a fibula, and a femur with a girth that is said to exceed that of "Sue"), and it should be noted that further research is needed to make proper, reliable estimates for the whole animal, thus, as of the present time, the remains of "Bertha" (which have been reconstructed too short and incomplete) cannot be used to confidently readjust the acceptable upper size limits of *Tyrannosaurus* yet. However, should the theories surrounding the specimen be supported by upcoming papers and by other experts, "Bertha" may prove to be the largest *T. rex* discovered so far, exceeding the estimates of "Scotty".

### Growth and Lifespan

*T. rexes* have an S-shaped growth curve, starting life with slow growth, then experiencing a great, rapid shift in size and physique before growth slows down again. Juveniles start out with larger eyes, a more gracile snout, slender legs, proportionally longer (but still tiny) arms, and an overall slimmer profile. Even at this young age, however, *T. rexes* can reach around half of their adult size, as is the case for specimen BMRP 2002.4.1 (nicknamed "Jane", previously regarded as a separate species called *Nanotyrannus*, though as of 2024, this theory has been subjected to debate once more), which measures 6.5 meters (21 feet) in length and approximately 639 - 1,269 kilograms (1,409 - 2,798 pound) in weight by the time it died at 11 years of age. Young *T. rexes* would remain under 1.8 metric tonnes (2 short tons) in weight until they are around 14 years old, by which point they grow at a dramatic rate, gaining an average of 600 kilograms (1,323 pounds) a year for the next four years. After this, growth slows down once more, as is the case for "Sue", which, despite being 28 years old, is only 600 kilograms (1,323 pounds) heavier than a 22 year-old Canadian *T. rex* specimen. *Tyrannosaurus* is also capable of slowing down its growth. Since larger animals require more food and are more vulnerable to environmental changes, the theropod's strategy of keeping its size low is a good means of adapting to times when resources are less abundant and conditions are harsher, with these studies also confirming that *Nanotyrannus* is simply a juvenile *Tyrannosaurus* following an analysis of the bone growth rings of both animals. Conversely, this control of growth could also help explain how "Scotty" grew to be the largest *T. rex* ever discovered so far despite being one of the youngest, indicating that the specimen may have lived during a time when resources were plenty and conditions were ideal.

***“ Decades of battling armored prey has scarred his body. One battle even cost him the tip of his tail. These new injuries are more serious. At his great age, infection is a real risk. River water could help to clean his wounds. He stands a good chance of living to fight another day... but that day could come sooner than expected. ”***

― **David Attenborough**, *Freshwater*
Once a *T. rex* reaches maturity at around 18 - 19 years of age, their growth slows down once more. The oldest *T. rex* specimen known so far is RGM 792.000 (nicknamed "Trix" after former Queen Beatrix of the Netherlands), which lived to be 30 years old, two years more than "Sue", as determined by their bone growth rings. Even so, most *T. rexes* don't get to live as long as either of these two specimens, for they usually die around six years after reaching maturity. In a 2013 lecture, Dr. Thomas Holtz attributes this to the fact that *T. rex* was an r-strategist, an animal that reproduces quickly, spawns many babies at a time, does not provide extensive parental care, and essentially "lived fast and died young", which matches the number Prehistoric Planet gives (15 hatchlings, two-thirds of which die off during their first year) and the loose parenthood provided by the *T. rex* father in Coasts. Gregory S. Paul also agrees that *T. rexes* reproduced quickly and died young, but instead attributes this short lifespan to the dangerous lives these predators led, with various fossils showing signs of vicious facial biting, bones broken and healed several times over, and even parasitic infections like an ancient form of Trichomonas gallinae. The second segment of Freshwater showcases the several injuries a tyrannosaur may suffer, with an old male bearing damage gained in prior battles (one of which cost him the tip of his tail), with the most recent one being a considerable slash on his side inflicted by a *Triceratops* he has recently brought down. While these can indeed prove risky (and may even cost him his life one day), these scars also serve as evidence that he faced several dangerous challenges in life and survived, with these testaments of his strength, experience, and triumph proving attractive to any onlooking female.

### Eyes

***“ The fields of vision of its two eyes overlap substantially, giving it very good depth perception, which would have made it a very effective predator. ”***

― **Professor Paul Barrett**, *Natural History Museum*
*Tyrannosaurus* has forward-facing eyes (topped with intimidating, prominent crests) that are 14 centimeters (5.5 inches) in diameter, the largest of any dinosaur (and perhaps of any land animal), giving it excellent binocular vision and remarkable night vision, making it a fearsome predator in any environment. However, in 2021, a comparison with the alvarezsaur *Shuvuuia* suggested that *T. rex* and *Dromaeosaurus* primarily hunted during daytime. Even so, Prehistoric Planet depicts *T. rex* and other carnivorous theropods like *Kuru kulla* (a relative of *Dromaeosaurus*) as being able to hunt effectively during the night.

***“ Tyrannosaurs have the largest eyes of any dinosaur, which gives them superb, low-light vision. And they're able to move through the forest in near-silence thanks to cushioned pads on their feet. ”***

― **David Attenborough**, *Swamps*
It is possible that *T. rex* was neither fully diurnal nor nocturnal, but cathemeral, active at irregular intervals throughout the day, much like lions. This idea appears to have been depicted to an extent on Prehistoric Planet, with a *T. rex* shown waking up from a short nap sometime after killing a *Triceratops* in Freshwater, and one *T. rex* waking up his brother to prepare for a night hunt in Swamps.

***“ Quetzalcoatlus, a giant pterosaur. One of the few creatures that will challenge an adult tyrannosaur. One strike from its six foot-long beak could easily cost T. rex an eye. ”***

― **David Attenborough**, *North America*
As a sight-reliant predator, the eyes of *Tyrannosaurus* are of utmost importance to it. Hence, when a fight is not worth the legitimate threat of losing sight completely (especially when it has lost sight in one eye due to prior experience), it would prioritize keeping its remaining means of sight intact.

### Jaws and Dentition

***“ T. rex has the most powerful jaws in nature, and can bite with the force of over five tons. ”***

― **David Attenborough**, *Coasts*
With a 1.5-meter (5-foot) skull weighing around 272 kilograms (600 pounds), *Tyrannosaurus rex* has one of the most powerful bites of any land predator, able to crush bone with strength sufficient to destroy a car. Estimates in 2012 set its maximum bite force to 6.4 tons (12,850 pounds), but 2018 revisions to these calculations set it back to 6.1 tons (12,100 pounds). To help generate these forces, *T. rex* can open its jaw up to 80 degrees, and it has a stiff skull, fixed and rigid to withstand the stress of its own bite. In Coasts, however, its bite force is moderated to "over five tons" (10,000 pounds), which is still impressively strong. Despite this power, certain prey animals with healed *Tyrannosaurus* bite marks on them (like *Triceratops* and *Edmontosaurus*, most specifically fossil DMNH 1943, an *Edmontosaurus annectens* with a *T. rex* bite on its tail) indicate that, given the size of *T. rex's* prey, it is still possible for victims of a *T. rex* attack to escape, maybe even fight back, and survive. In the fifth segments of Swamps, an *Edmontosaurus* managed to survive several bites and even put up a decent struggle against its attacker before finally being brought down by the combined effort of two *T. rexes*.

***“ Tyrannosaurus rex. North America's top predator. With his six inch-long teeth, tearing through an Alamosaur's tough skin is not a problem. ”***

― **David Attenborough**, *North America*
The teeth of *T. rex*, numbering around 50 - 60, measure around 30 centimeters (12 inches) long, the largest known of any carnivorous dinosaur. It should be noted, however, that the lower half of the tooth is embedded in the animal's gums as the root, hence, Prehistoric Planet only brings up the length of the exposed part of the tooth, the crown. Compared to most carnivorous dinosaurs, which have thin, blade-like teeth for tearing through flesh, *T. rex* teeth are robust and reinforced with ridges, allowing the teeth to withstand the stresses of both the animal's own bone-crushing bite and the struggles of captured prey. While studies regarding the matter are still debated, it is now believed that, unlike crocodiles, which have exposed teeth that are kept moist by their aquatic habitats, *T. rex* and other theropods kept their teeth concealed within lips, much like lizards and other primarily-terrestrial animals, thus protecting their enamel from degradation. As is the case for most reptiles, *T. rex* would have constantly lost and replaced all of its teeth, shedding and regrowing a few thousand in its lifetime.

It was once proposed that *T. rex* killed prey with very infectious saliva, much like a Komodo Dragon, with the serrations in their teeth retaining pieces of previous meals to cultivate bacteria, though the tooth serrations of tyrannosaurs are cube-shaped, not rounded like those of a Komodo Dragon. Today, this theory is not supported, since Komodo Dragon saliva is no different from those of other carnivores. Instead, they relied on a combination of shock, blood loss, venom (Komodo Dragons, like all monitor lizards, possess venom glands in their lower jaws, allowing them to inhibit blood clotting, lower blood pressure, paralyze muscles, and induce hypothermia), and the harsh conditions of their habitat (Komodo Dragon victims get infected with sepsis not due to the presence of special, highly septic saliva, but due to the feces-filled waters and overall warm conditions of the environment which help promote bacterial growth). Evidence of prey that survived and healed from a *T. rex* attack (like the DMNH 1943 *Edmontosaurus* specimen) make it highly unlikely that *T. rex* had a venomous bite, and, with its six-ton bite force being one of the most powerful of any land animal that ever lived, the evolution and usage of toxins is very much unnecessary. However, there still remained the threat of a *T. rex* bite getting infected, given the warm, wet environments where *T. rex* lived in, much like the habitat of Komodo Dragons today.

### Arms

*Tyrannosaurus* is also known for its notoriously-short arms, each three feet long and ending in two curved claws. However, these arms are deceptively strong due to extremely thick bones and powerful muscles. The biceps alone are able to lift 200 kilograms (441 pounds), with additional muscles contributing even more power. Furthermore, the arms also show stress fractures, damages formed by regular usage and not isolated, one-off events, providing further evidence that these arms were not vestigial.

### Skin

Although feathers are known in basal tyrannosauroids like the 9-meter (30-foot) proceratosaurid *Yutyrannus huali* (the largest feathered animal known so far), *T. rex* skin impressions lack direct evidence of feathers, indicating that *T. rex* and other advanced members of the tyrannosauroid superfamily were, for the most part, scaly. However, based on the exhibit by paleontologist Mark Norell, the *T. rex: The Ultimate Predator*, recent and more accurate studies helped the reconstruction of a juvenile *T. rex* model. Hatchlings may have been covered in feathers, which prompted the scientists involved to propose that, while *T. rex* was primarily covered in scales, it also had a mullet of feathers on its head, neck, and tail. With these findings, Prehistoric Planet chose to portray *T. rex* with a coat of feathers when young, the animal gradually losing its plumage as it grows, until all that is left on the adults are some faint, almost hair-like remnants.

### Speed

As a theropod, *T. rex* also boasts remarkably muscular, powerful legs, with three large, clawed toes along with a smaller fourth digit that didn't touch the ground, indicating its vestigial nature. These legs would have served multiple purposes, including kicking and stomping on prey, walking, running, and potentially even swimming, as suggested on Prehistoric Planet. While its speed isn't explicitly stated on the show, it is believed that, despite being incredibly robust, with a body made stocky by layers of muscle and fat, *T. rex* is capable of running at decent speeds ranging from 4.5 - 6.8 meters (15 - 22 feet) per second, or 16 – 24 kilometers (10 - 15 miles) per hour to 20 meters (66 feet) per second, or 72 kilometers (45 miles) per hour, though these have been considered infeasible even as far back as 2002.

More recent, up-to-date studies have cast further doubt on these high-speed capabilities. A 2017 study brings up how, due to Newton's laws of motion, mass must overcome inertia, thus, a larger animal, despite having more muscles to power their limbs, would not always be faster than smaller animals with lesser muscles, as proven by the cheetah, which is faster than beetles, mice, rabbits, and elephants. In the study, a mathematical model based on an animal's weight and the medium it moves in (land, water, or air) is used on *T. rex*, *Triceratops*, *Brachiosaurus*, and others, with the results of the complex simulation indicating that *T. rex* could only run up to 27 kilometers (17 miles) per hour, and it would likely exhaust itself before reaching its top speed due to anaerobic metabolism. Furthermore, another 2017 study, focused on the skeletal loads of large theropods, brings up how speeds over 18 kilometers (11 miles) per hour would have shattered the bones of *T. rex* and other large carnivores like *Giganotosaurus*, though one counterargument in 2019 also discusses how *T. rex* and other tyrannosaurids were at least more maneuverable and agile compared to allosauroids, and thus would not have been subject to the exact same arguments.

***“ Time to spring the trap. One T. rex rushes out! The herd panics, and bolts to where the other T. rex is waiting... in ambush. ”***

― **David Attenborough**, *Swamps*
A study in 2021 calculated a rhythmic, energy-efficient walking speed of 1.28 meters (4 feet, 2 inches) per second, or 4.6 kilometers (3 miles) per hour for *T. rex*. With this being the current consensus regarding *T. rex's* speed, it likely hunted its prey via ambush, since some of them, like *Edmontosaurus*, are believed to be twice its speed, as stated in Swamps, the likely basis of this being a study in 2009, which indicates that *Edmontosaurus* can reach a speed of 15.7 meters (52 feet) per second, or 57 kilometers (35 miles) per hour, when galloping on all fours, and 14 meters (46 feet) per second, or 50 kilometers (31 miles) per hour, when running on two legs, double the speed of the results that consistently come up in modern *T. rex* speed calculations. However, Dr. Darren Naish later clarified that the idea of *Edmontosaurus* being twice as fast as *T. rex* was an error, and both animals actually had a similar top speed, meaning that, given the modern estimates of the maximum speed of *T. rex* (which was calculated almost a decade after the studies regarding the running speed of *Edmontosaurus*, and thus, are more in-line with the current understanding of these animals), *Edmontosaurus* likely also ran at speeds of around 25 - 30 kilometers (15.5 - 19 miles) per hour, making it easier for a *T. rex* to catch up to one of these hadrosaurs (though ambushing prey is still more preferable for predators since it would help conserve effort, energy, and time).

### Sounds

*Tyrannosaurus rex* and other large theropods are usually depicted in popular culture as roaring, with the (oftentimes modified and distorted) sound effects of various big cats and other large mammals like elephants being used. However, current scientific theories suggest that, due to their different throat anatomy, dinosaurs would not have roared or vocalized the same way mammals do. However, this does not mean that they outright lacked the ability to roar in their own way, as it is believed that they may have at least growled and bellowed like crocodiles, or let out bird-like vocalizations, some of which are done without even having to open their mouth since they only need to accumulate and move enough air to vibrate their throats or other internal structures. Some sounds produced by various animals, both living and extinct, may not even be audible to other creatures that do not possess the same hearing range, an advantage for *Tyrannosaurus* and other animals which possess ears capable of detecting low frequencies over long distances, yet another valuable hunting tool that allows them to not only accurately hone in on prey from far away, but also to engage in seemingly silent, secret communication.

On Prehistoric Planet, *T. rex*, along with most of the other dinosaurs in the series (especially other theropods), communicated with crocodile-like growls and hisses as well as low drumming and booming sounds like an ostrich or emu, as shown in the second segment of Freshwater, where the old male *T. rex* and a younger female bellow and growl at each other at first, then greet each other with close-mouthed throaty rumbling when the situation has become less hostile.

The sounds of the juvenile tyrannosaurs were originally meant to be modified crocodile sounds, though when these seemed insufficiently one-dimensional and too obvious, Prehistoric Planet turned to various bird vocalizations. Among those used are the pitch-changed calls of a common starling, and the slowed down cries of a cactus wren.

### Prehistoric Planet's Depiction

*Main: *Tyrannosaurus rex* on Prehistoric Planet*

Main: *Tyrannosaurus rex* on Prehistoric Planet

On Prehistoric Planet, *Tyrannosaurus rex* is depicted with mottled brown and cream skin, providing the hunter a degree of countershading (which many animals, predator and prey alike, use to enhance their camouflage depending on the light and angle at which they are viewed). It has distinctive streaks of color along its mouth that resemble external teeth, with its actual teeth covered with fleshy lips. Of note, on the show, the skin patterns of *T. rex* very faintly resembles that of its Asian relative *Tarbosaurus*, showing the connection between the two. As with the other tyrannosaurs featured on Prehistoric Planet, *T. rex* bears stripes on its snout, and it's been theorized that this is a trait that they all inherited from their last common ancestor. While there is no confirmation of this being the case, Dr. Darren Naish, Prehistoric Planet's lead consultant, shared this fan theory, indicating a degree of support and plausibility for the idea.

The show also depicts *T. rex* with faint sexual dimorphism. Only one adult female is shown in the series, during the second segment of Freshwater, and she is depicted with slightly less-prominent eye crests as well as slightly lighter skin color (fitting given how, in most animals, the females have duller coloration compared to their more vibrantly-colored male counterparts), though this can also be attributed to her being younger than the old male she met as well as individual variation.

***“ Surely, one of the most remarkable animals that have ever existed - and certainly one of the most famous - is a dinosaur. Tyrannosaurus rex. An animal to spark the imagination for all of us. What kind of an animal was it? What did it look like? How did it live? ”***

― **David Attenborough**, *Prehistoric Planet Season 1 episode opening*
A *T. rex* skeleton appears in the opening of every episode of Prehistoric Planet's first season. *T. rex* was first featured in the first segment of Coasts, where a father leads his five chicks to an offshore island to feed, remain safe, and hone crucial hunting skills. In the second segment of Freshwater, an old male *T. rex* is shown with a freshly-slain *Triceratops*, eventually meeting a female *T. rex* by a river and mating with her. A pair of subadult *T. rex* brothers appear in the fifth, final segment of Swamps, where they ambush an *Edmontosaurus* at night in the forests of the Hell Creek Formation. *T. rex* makes one last appearance in North America, where one male gets into a fight with two *Quetzalcoatlus* over a dead *Alamosaurus* by the coast of the Javelina Formation.

*T. rex* is also the subject of two Uncovered segments, the first being "Could T. rex Really Swim?", which discusses the idea of large theropods swimming, and the second being "How Good Were T. rex Senses?", which explains in great detail the acute senses that made *T. rex* such a formidable hunter. Footage of *T. rex* facing off against the two *Quetzalcoatlus* in North America is also used for the Uncovered segment "Prehistoric Planet: Uncovered - What Else Lived Alongside The Dinosaurs?", specifically the part regarding pterosaurs.

## Paleoecology

### Paleoenvironment

*Main: Hell Creek Formation, Javelina Formation*

Main: Hell Creek Formation, Javelina Formation

***“ Across this vast continent, there are over a hundred thousand square miles of swamplands. And most of them remain flooded all year-round. ”***

― **David Attenborough**, *Swamps*
*Tyrannosaurus rex* lived 68 - 66 million years ago in Laramidia, an island continent that would one day become western North America, which, by that time, was nearly split in half by an inland sea. Its range goes as far north as Canada, all the way down to at least New Mexico and Texas in the south, as indicated by fossils in the Javelina Formation. While *T. rex* appears to prefer subtropical inland forests, swamps, rivers, and open plains (all the aforementioned environments are seen in the Hell Creek Formation, which, though warmer than Montana and South Dakota today, was kept humid by sufficient levels of rainfall), *T. rex* remains have also been found in coastal and even semi-arid regions like the Javelina Formation.

The origin of *Tyrannosaurus rex* is still not entirely clear. There was once the idea that *T. rex* descended from North American tyrannosaurines like *Daspletosaurus*, though the current prevailing theory is that *T. rex* came from tyrannosaurines like *Tarbosaurus* or *Zhuchengtyrannus*. In 2024, however, a newly-described species, *Tyrannosaurus mcraeensis* of the Hall Lake Formation in New Mexico, once again supports the theory that *T. rex* descended from North American tyrannosaurines. *Tyrannosaurus mcraeensis* lived approximately 73 - 71 million years ago, around 3 - 5 million years before *T. rex* first appeared, possessing a less-prominent chin, a shallower lower jaw (which likely provides a weaker bite force), blunter teeth, and a slightly less-robust build more in line with *Tarbosaurus* and *Zhuchengtyrannus*, thus also lending some credence to the idea that *Tyrannosaurus* descended from Asian ancestors that crossed a land bridge. It should be noted, however, that, as a relatively recent discovery, the validity of *T. mcraeensis* is still debatable, and it could also simply be a *T. rex* that lived during a significantly earlier time.

### Paleofauna

***“ Here, in spring, new plant growth creates new feeding grounds for the gathering herds. But where there are large numbers of plant-eaters, there are great hunters... ”***

― **David Attenborough**, *Swamps*
No matter the region (as long as it is land-based), *Tyrannosaurus rex* dominated as the apex predator, with most of the other predatory niches between the adults and small carnivorous dinosaurs being filled in by young *T. rexes* of various growth stages. Given its status as top hunter, *T. rex* would have been one of the most widespread and most successful animals within its range, with studies in 2021 postulating that around 20,000 adult *T. rexes* would have been alive at any given time, resulting in a total of 2.5 billion *T. rexes* existing throughout their two million years of existence. However, various uncertain factors like variability in body sizes, habitat preferences, survival rates, and others make the theories put forth by these population studies questionable. Regardless, *T. rex* would have coexisted with animals like *Ankylosaurus*, *Edmontosaurus*, *Pachycephalosaurus*, and *Triceratops*, as well as some dromaeosaurs like *Acheroraptor* and troodontids like *Pectinodon*. In its southern range, *T. rex* would have lived alongside *Alamosaurus* (the only sauropod in North America following around 30 million years of sauropod absence on the continent) and the only other predator that could possibly challenge it, *Quetzalcoatlus* (though azhdarchid cervical vertebra found in southeast Montana implies that *Quetzalcoatlus* may have also been present further up north in *T. rex's* range).

In a 2011 study that estimated the proportions of large-bodied dinosaurs in the Hell Creek Formation, it was revealed that *Tyrannosaurus rex* made up 24% of the dinosaurs found in Hell Creek, being second only to *Triceratops* (which makes up 40% of Hell Creek's dinosaur population).

As one of the last non-avian dinosaurs, *T. rex*, along with most of the animals it coexisted with, would have bore witness to the K-Pg Extinction Event 66.043 million years ago, a catastrophe that would ultimately wipe out three-quarters of all life on Earth, including all non-avian dinosaurs.

### Hunting Tactics and Feeding Preferences

***“ T. rex are built for hunting large herbivores, and many of those have evolved heavy defensive weapons. ”***

― **David Attenborough**, *Freshwater*
*Tyrannosaurus rex* is the apex predator of its environment. With its six-ton bone-crushing bite, it can overcome heavily-armored prey like *Triceratops* and *Ankylosaurus*, though there is also a good chance that, even if a *T. rex* survives its encounters with such dangerous prey, it will not come out of these encounters unscathed, with gore, infection, and even broken bones being possible risks. While known for its brute force, as a theropod, *T. rex* possesses predatory cunning and tactics. In order to hunt an *Edmontosaurus* successfully, two *T. rex* brothers stalked a herd of them in the darkness of the night, deliberately causing noise while hidden in the cover of the forest to cause the herd to panic and eventually separate, isolate, and ambush one member, similar to how a few *Dromaeosaurus* successfully caused an *Edmontosaurus* herd to hastily cross a rapid icy river in the first segment Ice Worlds (resulting in the death of at least one member), and how *T. rex's* Alaskan relative *Nanuqsaurus* relied on spreading panic to cause an *Ornithomimus* to eventually make a critical mistake that guaranteed its capture in the fifth segment of North America.

Wherever tyrannosaurs ruled, their juveniles tend to occupy the various predatory niches between the adult tyrannosaurs and other hunters. Although the youngsters tend to lack the bone-crushing capabilities of their more mature counterparts, they are still deadly hunters in their own right. One of the most significant fossils of any dinosaur is the "Dueling Dinosaurs" specimen of Hell Creek, which preserves an adolescent *T. rex* locked in combat with a *Triceratops horridus*. Entombed in sandstone, the two skeletal remains are considered to be one of the most preserved and most complete specimens of both *T. rex* and *Triceratops*, showcasing the sort of prey *Tyrannosaurus* went after and what sort of threat it posed, even when not fully mature.

***“ A group of Edmontosaurs. They lack armor, but they're as big as T. rex, and twice as fast. To catch one needs cunning. ”***

― **David Attenborough**, *Swamps*
Due to its great physique being built more for power than speed, *Tyrannosaurus*, like its earlier relative *Daspletosaurus*, likely preferred to go after slower, more heavily-armed prey. In the second segment of Freshwater, *T. rex* is seen feeding on a *Triceratops* starting from the neck. As a study in 2012 suggests, *T. rex* likely focused on the nutrient-rich neck muscles behind the frill of a *Triceratops* (which, in life, were necessary to help the ceratopsian support the great weight of its head).

Even so, these muscular theropods are still very much capable of going after lighter, quicker prey, with the fifth segment of Swamps showing them relying on smart tactics like hunting at night, ambush, and, on occasion, even cooperative hunting to tackle the challenges posed by fast-moving prey. It is also important to note that even *Edmontosaurus*, which is supposedly one of the easier targets to tackle, is not the defenseless pushover that popular culture makes it out to be. Given its size and mass, *Edmontosaurus* is a powerful animal capable of fighting off attackers with its muscular limbs and tail. Evidence of this can be seen in DMNH 1943, an *Edmontosaurus annectens* specimen with a *T. rex* bite on its tail that shows signs of healing, indicating that the animal escaped and survived the attack (and may have potentially fought the *T. rex* off). The original plan for the fifth segment of Swamps even involved two juvenile *T. rexes* attacking an adult *Edmontosaurus*, only to be beaten up. While this particular idea ultimately never came to pass, the final version of events showed that it still takes a considerable amount of experience, skill, and even luck for a *T. rex* to bring down an *Edmontosaurus*.

***“ The island offers safety and the promise of food. Giant, two-tonne turtles are here to nest. But this is the one that has drawn him here. It's dead, and the tyrannosaur has smelt its rotting body. If he can just get to the underbelly, he will have over two thousand pounds of easy meat. ”***

― **David Attenborough**, *Coasts*
Even so, as a predator, *T. rex* would not have been averse to scavenging to save effort and energy. In Coasts, a *T. rex* risks his life (and that of his five hatchlings, one of which gets eaten by a mosasaur) to reach an island where there's an already-dead turtle he can feast on without any effort. In North America, a *T. rex* also closes in on the smell of a dead *Alamosaurus* to feed on it, driving away a trio of troodontids in the process, though the *T. rex* himself ends up getting challenged by a pair of *Quetzalcoatlus*, which also take advantage of the great feeding opportunity.

### Social Habits

In terms of social behavior, there is barely any direct evidence for such in *Tyrannosaurus*, which appears to be a mostly solitary animal. Nevertheless, tyrannosaurs seem to show some evidence of pack behavior, with an Uncovered segment dedicated to proof of pack-hunting in relatives like *Nanuqsaurus*, and fossils from South Dakota revealed three *T. rexes* within close proximity of each other. The episode Swamps reflects the idea that dinosaurs maintained family ties throughout their lives by showing two subadult *Tyrannosaurus* brothers hunting prey together.

Additionally, there are instances where individuals may encounter each other and not immediately engage in hostilities. In such cases, initial contact may be tense, but it can transition into courtship and mating, as depicted in Freshwater. The male *T. rex* is shown rearing up and displaying his throat, to make him appear tall and powerful to any observing females, while also showing his vulnerability (in a form of trust) and non-aggression (similar to how crocodilians display their throats to indicate that they have no hostile intent).

***“ The facial area of a tyrannosaur is very sensitive to touch, and they nuzzle. ”***

― **David Attenborough**, *Freshwater*
The snouts of tyrannosaurs contain numerous nerve endings, facilitating face-to-face interactions, whether they are intimate or aggressive in nature (evidence of aggressive interaction comes in the form of several facial bite marks found on various theropods, while rubbing an nuzzling behavior can still be seen in reptiles today, like crocodiles and monitor lizards). During mating, *T. rexes* are depicted assuming a sitting position, similar to the posture observed in present-day birds and reptiles, rather than the long-held belief of a standing position.

Due to a lack of evidence, it is unclear whether tyrannosaurs went their separate ways after mating, or stuck together at least for a while to raise their brood. Given the state of most fossil finds, it appears that such partnerships were only temporary, and outside of the mating season, tyrannosaurs lived alone, matching behavior seen in tigers today.

### Parental Habits

***“ A full grown T. rex is the planet's most powerful predator, but today he's just being father. ”***

― **David Attenborough**, *Prehistoric Planet - Official Sneak Peek*
Because of the rarity of fossilized tyrannosaur nests and juveniles, the parental habits of *Tyrannosaurus* are not exactly clear. To this day, there is no direct evidence to support or deny the various ideas regarding how juvenile *T. rexes* are raised, be it by one parent, both parents, or no parents. Assuming at least one parent raised the hatchlings, it isn't known how long they reared them either.

Even so, based on crocodiles, birds, other theropods like oviraptorids, and even other dinosaurs that are not so closely related like the hadrosaur *Maiasaura*, it is possible of *T. rex* did indeed raise its young. Taking inspiration from some birds, Prehistoric Planet depicts only the male *T. rex* taking care of his offspring to a degree, though the show depicts *T. rex* more like an r-strategist species, given how it is stated that they spawn at least 15, with around two-thirds dying off in their first year (r-strategist animals rely on multiple offspring, many of which are expected to perish before reaching adulthood). The *T. rex* in Coasts is also shown leading their children around to safer places where more food can be found, but does not seem to provide extensive parental care, for, unlike *Pectinodon* and *Nanuqsaurus*, two theropods on the show that still provide food for their hatchlings (and thus appear to be K-strategists, animals that provide extensive parental care to their offspring), *T. rex* refuses to share the turtle he scavenged with his children, forcing them to find food on their own. This aspect also seems to be in-line with the r-selection strategy, which involves a lesser degree of parental care.

***“ The young are keen for a taste, but he's not sharing it. It's time for them to learn to hunt for themselves. ”***

― **David Attenborough**, *Coasts*
Even so, this lessened degree of guidance and assistance can also be a good parenting tactic in its own right. In forcing the juveniles to get their own food rather than sharing meals with their parent, they are encouraged to learn and develop the necessary skills for survival and self-sufficiency early on. Having lead them to an offshore island where food is plenty, the *T. rex* in Coasts at least ensured that his chicks can practice their skills in peace and safety. As they grow older, the juveniles may potentially even assist their parent in the hunt, and eventually, fend for themselves as fully-independent individuals.

### Competitive Habits

***“ But 66 million years ago, venturing into coastal waters would not have been without risk, even for T. rex. Mosasaurs hunted beneath these waves, and young tyrannosaurs, particularly, would have been a valuable meal for these formidable aquatic hunters. T. rex may have been strong swimmers, but they could only have been brief visitors to the prehistoric oceans. Although their name means 'Tyrant Lizard King', they could never have ruled the waves while the mosasaurs patrolled the coasts. ”***

― **David Attenborough**, *Prehistoric Planet: Uncovered - Could T. rex Really Swim?*
In terms of the competition with other carnivores, despite being the apex predator of North America, *T. rex* has its fair share of opponents. As shown in Coasts, when in the sea, *T. rex* could potentially face mosasaurs, which, at twice its size and mass, are the largest predators of Earth during the Late Cretaceous Period. However, an adult *T. rex* can still defend itself in the water very effectively, so the mosasaur wisely picked off one of the tyrannosaur's five juveniles instead.

***“ Not many can intimidate North America’s top predator, T. rex, whose size and bite are a deadly combo — except for a giant winged foe. ”***

― The official Apple TV+ episode synopsis for *North America*
*T. rex* could also potentially get into conflict with the giant azhdarchid *Quetzalcoatlus*, as seen in the first segment of North America, where two of the pterosaurs challenged a *T. rex* for feeding rights to an *Alamosaurus* carcass. *T. rex* weighs 30 - 40 times greater than the lightweight pterosaur, has a powerful, six-ton bite that can crush bone, and, being capable of short bursts of speed as well as walking at a decent pace, it is by no means a lumbering animal. In the first segment of North America, a lone *Quetzalcoatlus* appeared a bit hesitant to approach a *T. rex* head on, though it slowly tried to creep in when the *T. rex* had its back turned, implying that it was still ready to try its chances even on its own. When a second *Quetzalcoatlus* arrived, however, the azhdarchids were more willing to exploit the few advantages they do have to challenge the *T. rex*. Due to their lighter build, large quadrupedal gait, and competent terrestrial mobility, they can move equally as fast and even be more agile than *T. rex* on the ground. Their ability to quickly quad-launch into the air at a moment's notice and attack from above is also a definitive advantage, though given the low agility of azhdarchids in the air compared to other types of pterosaurs, they may need large, open areas like a beach or plain to fully take advantage of their flight capabilities in such a conflict. *Quetzalcoatlus* also has a six-foot beak that gives it better reach, allowing it to strike opponents from a relatively safe distance. While these don't guarantee that they will always have the upper hand in such situations, with all these traits, *Quetzalcoatlus* can effectively harass comparatively less-nimble foes and even pose legitimate dangers (like permanent blindness in both eyes, which can be a death sentence for any sight-reliant predator), all of which can prove sufficient to get even the likes of *T. rex* to leave if the risks they pose outweigh the urgency to feed.

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## Trivia

### Speculation

* It is unknown how exactly dinosaurs drank water. Prehistoric Planet chose to depict various types of dinosaur drinking water in different ways, with theropods shown scooping up water with their lower jaws rather than lapping it with their tongues or sucking it up. In the fourth segment of Deserts, *Mononykus*, *Therizinosaurus*, and *Tarbosaurus* drink water in this manner, and *Tyrannosaurus* is later depicted doing the same in the second segment of Freshwater.

### Other

* The adult male *T. rex* in Coasts has been given the nickname "Hank" by various fans of the show.
* *T. rex* is one of the two animals that appeared in multiple segments shown eating in all the segments it was featured in. It ate a protostegid in the first segment of Coasts, fed on a *Triceratops* that it hunted offscreen in the second segment of Freshwater, engaged in cooperative nocturnal hunting to bring down an *Edmontosaurus* in the fifth segment of Swamps, and scavenged an *Alamosaurus* in the first segment of North America. The other such animal to hold that distinction is *T. rex's* Alaskan relative *Nanuqsaurus*, which hunted *Pachyrhinosaurus* in the sixth segment of Ice Worlds and *Ornithomimus* in the fifth segment of North America. Close contenders include
	+ *Velociraptor*, which ate a lizard in the second segment of Deserts and begun consuming a *Prenocephale* by the end of the second segment of Badlands, but only ran off with a juvenile azhdarchid to eat it offscreen by the end of the first segment of Freshwater.
	+ *Hatzegopteryx*, which ate a juvenile *Zalmoxes* in the seventh segment of Forests and a juvenile *Tethyshadros* in the second segment of Islands, though in its third appearance, it only used a juvenile *Tethyshadros* as a reusable proof of strength, with neither the male nor the female he mated with actually consuming it by the end of the sixth segment of Islands.

## References

### General

1. ↑ 1.0 1.1 1.2 How well do you know SUE?
2. ↑ 2.0 2.1 2.2 2.3 SUE the *T. rex*
3. ↑ 3.0 3.1 3.2 3.3 3.4 A Computational Analysis of Limb and Body Dimensions in *Tyrannosaurus rex* with Implications for Locomotion, Ontogeny, and Growth
4. ↑ 4.0 4.1 4.2 An Older and Exceptionally Large Adult Specimen of *Tyrannosaurus rex*
5. ↑ 5.0 5.1 5.2 Paleontologists identify biggest *Tyrannosaurus rex* ever discovered
6. ↑ 6.0 6.1 Mass Estimates: North vs South Redux
7. ↑ 7.0 7.1 7.2 7.3 7.4 SUE at The Field Museum
8. ↑ 8.0 8.1 Correction to 'Estimating maximum bite performance in *Tyrannosaurus rex* using multi-body dynamics'
9. ↑ 9.0 9.1 About Dinosaur Teeth
10. ↑ 10.0 10.1 Estimating cranial musculoskeletal constraints in theropod dinosaurs
11. ↑ 11.0 11.1 Mesozoic vertebrate life
12. ↑ 12.0 12.1 12.2 Walk the dinosaur: New biomechanical model shows *Tyrannosaurus rex* in a swinging gait
13. ↑ 13.0 13.1 13.2 New Study Finds *T. rex* Walked at a Slow Pace of Three Miles Per Hour
14. ↑ 14.0 14.1 Why *Tyrannosaurus* was a slow runner and why the largest are not always the fastest
15. ↑ 15.0 15.1 Tyrannosaur life tables: an example of nonavian dinosaur population biology
16. ↑ 16.0 16.1 Trix the *T. rex* makes her mark on Leiden in new exhibition
17. ↑ A high-resolution growth series of *Tyrannosaurus rex* obtained from multiple lines of evidence
18. ↑ Molina-Pérez; Larramendi (2016). *Récords y curiosidades de los dinosaurios Terópodos y otros dinosauromorfos*. Barcelona, Spain: Larousse. p. 268
19. ↑ The Tyrant Lizard King, Queen and Emperor: Multiple Lines of Morphological and Stratigraphic Evidence Support Subtle Evolution and Probable Speciation Within the North American Genus Tyrannosaurus
20. ↑ Should T. rex be 3 species? New study sparks fierce debate.
21. ↑ Clawson, Steve (@daspleto) (May 17, 2023) on Twitter, discussing the addition of the "Bertha" specimen to the Dickinson Museum Center
22. ↑ Fowler, Denver (May 17, 2023) on Facebook, discussing the possibility that "Bertha" may be bigger than "Scotty"
23. ↑  Fowler, Denver (July 5, 2023) on Facebook, discussing the remains of "Bertha"
24. ↑ Taxonomic Status of *Nanotyrannus lancensis* (Dinosauria: Tyrannosauroidea)—A Distinct Taxon of Small-Bodied Tyrannosaur
25. ↑ Study Aims to Bring a Tinier Tyrannosaur Back From Oblivion - New research is trying to remake the case that fossils known as *Nanotyrannus* were their own species, rather than a teenage *Tyrannosaurus rex*
26. ↑ Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs
27. ↑ Growing up *Tyrannosaurus rex*: Osteohistology refutes the pygmy "*Nanotyrannus*" and supports ontogenetic niche partitioning in juvenile *Tyrannosaurus*
28. ↑ These sleek predatory dinosaurs really are teenage *T. rex*
29. ↑ "Chapter 18: The Extreme Life Style and Habits of the Gigantic Tyrannosaurid Superpredators of the Cretaceous North America and Asia"
30. ↑ Evolution of vision and hearing modalities in theropod dinosaurs
31. ↑ *Shuvuuia*: A dinosaur that hunted in the dark
32. ↑ 32.0 32.1 A *T. rex* bite could have crushed a car. Here's how.
33. ↑ Estimating maximum bite performance in *Tyrannosaurus rex* using multi-body dynamics
34. ↑ 34.0 34.1 34.2 Evidence of predatory behavior by carnivorous dinosaurs
35. ↑ *T. rex* Had Lips That Concealed Its Teeth, Study Says
36. ↑ Theropod dinosaur facial reconstruction and the importance of soft tissues in paleobiology
37. ↑ 1999. The teeth of the *Tyrannosaurus*. *Scientific American* 281: 40-41.
38. ↑ The serrated teeth of tyrannosaurid dinosaurs, and biting structures in other animals
39. ↑ The Complete T. Rex: How Stunning New Discoveries are Changing our Understanding of the World's Most Famous Dinosaur copyright 1993 by John R. Horner: pp 214-215
40. ↑ 40.0 40.1 Anaerobic and aerobic bacteriology of the saliva and gingiva from 16 captive Komodo dragons (*Varanus komodoensis*): new implications for the "bacteria as venom" model
41. ↑ A central role for venom in predation by *Varanus komodoensis* (Komodo Dragon) and the extinct giant *Varanus* (*Megalania*) *priscus*
42. ↑ Why tyrannosaurid forelimbs were so short: An integrative hypothesis
43. ↑ Black, Riley. Scientists Discover a Gigantic Feathered Tyrannosaur. *Smithsonian Magazine*
44. ↑ Katz, Brigit. 2012. T. Rex Was Likely Covered in Scales, Not Feathers. *Smithsonian Magazine*
45. ↑ Baby *T. rex* Was an Adorable Ball of Fluff
46. ↑ Sexton, Chrissy. 2019. New evidence reveals the real *T. rex* had feathers and massive eyes
47. ↑ *Tyrannosaurus* was not a fast runner
48. ↑ Investigating the running abilities of *Tyrannosaurus rex* using stress-constrained multibody dynamic analysis
49. ↑ Lower rotational inertia and larger leg muscles indicate more rapid turns in tyrannosaurids than in other large theropods
50. ↑ Virtual Palaeontology: Gait Reconstruction of Extinct Vertebrates Using High Performance Computing
51. ↑ Did Dinosaurs Roar?
52. ↑ What did Dinosaurs Sound Like?
53. ↑ The phylogeny and evolutionary history of tyrannosauroid dinosaurs
54. ↑ A giant tyrannosaur from the Campanian–Maastrichtian of southern North America and the evolution of tyrannosaurid gigantism
55. ↑ Scientists conclude New Mexico fossil is new *Tyrannosaurus* species
56. ↑ How Many *Tyrannosaurus rexes* Ever Lived on Earth? Here’s a New Clue.
57. ↑ Absolute abundance and preservation rate of *Tyrannosaurus rex*
58. ↑ Population sizes of *T. rex* cannot be precisely estimated
59. ↑ With what precision can the population size of *Tyrannosaurus rex* be estimated? A reply to Meiri
60. ↑ An Azhdarchid Pterosaur Cervical Vertebra from the Hell Creek Formation (Maastrichtian) of Southeastern Montana
61. ↑ Review of taxonomy, geographic distribution, and paleoenvironments of Azhdarchidae (Pterosauria)
62. ↑ Dinosaur Census Reveals Abundant *Tyrannosaurus* and Rare Ontogenetic Stages in the Upper Cretaceous Hell Creek Formation (Maastrichtian), Montana, USA
63. ↑ Dinosaur extinction battle flares
64. ↑ 'Dueling Dinosaurs' fossil, hidden from science for 14 years, could finally reveal its secrets
65. ↑ North Carolina Museum of Natural Sciences to receive the "Dueling Dinosaurs"
66. ↑ How to eat a *Triceratops*: large sample of toothmarks provides new insight into the feeding behavior of *Tyrannosaurus*
67. ↑ *Tyrannosaurus rex* 'hunted in packs'

### Dr. Darren Naish

1. ↑ 1.0 1.1 *T. rex* is portrayed engaging in a nocturnal hunt to show the animal in a new light, justified by the fact that it had eyeballs that can be as much as 14 centimeters (5.5 inches) across, likely one of the largest of any land animal, though admittedly, there should have been more tissues around the edges of its eyes on the show.
2. ↑ Juvenile *T. rexes* had proportionally longer forelimbs compared to the adults, but these were still small.
3. ↑ The idea that *Edmontosaurus* is twice as fast as *T. rex* is a mistake, the narration was instead supposed to state that both animals had a similar top speed.
4. ↑ Dinosaurs may have been capable of open-mouth vocalizations like crocodylians.
5. ↑ The snout stripes of the tyrannosaurs featured on Prehistoric Planet is likely a trait they inherited from their last common ancestor, serving as proof of their relationship.
6. ↑ 6.0 6.1 The fifth segment of Swamps has two subadult *T. rex* brothers hunting together in order to show the idea that dinosaurs of many sorts likely maintained familial social bonds throughout life.
7. ↑ *Edmontosaurus* is far from defenseless. The original plan for the *T. rex* hunt was to show two juvenile *T. rexes* (as opposed to the subadults of the final version) trying to take on an adult *Edmontosaurus*, only to be beaten back, though this particular idea never ended up getting developed.
8. ↑ It still takes a considerable amount of experience, skill, and luck for a *T. rex* to tackle an *Edmontosaurus* and finally subdue it with a bite to the throat.
9. ↑ Nuzzling among reptiles can be observed in crocodiles and monitor lizards.

### Dr. Thomas Holtz

1. ↑ 1.0 1.1 Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages
2. ↑ Dr. Thomas R. Holtz argues against the separation of *Nanotyrannus*, but does not completely rule it out
3. ↑ The Life and Times of *Tyrannosaurus rex*, with Dr. Thomas Holtz

### Prehistoric Planet

1. ↑ As stated in Prehistoric Planet: Uncovered - How Good Were T. rex Senses?
2. ↑ Prehistoric Planet: The Official Podcast - Digging Up The Evidence
3. ↑ 3.0 3.1 As indicated by the name of the *T. rex* pair's theme in the Official Soundtrack, "Tyrannosaurus Brothers".
4. ↑ As stated in Prehistoric Planet: Uncovered - Could Giant Pterosaurs Really Hunt on the Ground?