T. rex Facts for Kids

T. rex quick facts

• T. rex lived closer in time to you than to Allosaurus, the big Jurassic hunter.
• Its first known bones were given another name, Manospondylus gigas, in 1892.
• As a teenager, SUE gained up to 2 kg (4.5 pounds) a day.
• No T. rex skin has been found from its back, the one place feathers could have been.
• In 2025, a study argued that fossils long thought to be young T. rex belong to a different dinosaur, Nanotyrannus.

What was Tyrannosaurus rex?

Tyrannosaurus rex was one of the biggest meat-eating dinosaurs that ever lived. Its full name is long, so most people shorten it to T. rex.

Scientists put it in a group called theropods, which were dinosaurs that walked on two legs, and many of them ate meat. Allosaurus and Spinosaurus were theropods too.

T. rex is also one of the best-studied dinosaurs on Earth. The Field Museum in Chicago counts more than 30 T. rex skeletons found so far. That is far more than most dinosaurs, so scientists know a lot about its size, its teeth and how it grew up.

What the name means and who named it

Tyrannosaurus rex means “tyrant lizard king”. A tyrant is a cruel ruler, and rex is the Latin word for king.

The name was given in 1905 by Henry Fairfield Osborn, a palaeontologist, which means a scientist who studies fossils. The bones he described had been dug up by a fossil hunter called Barnum Brown.

Brown found the first known skeleton in Wyoming, USA, in 1900, and two years later, in 1902, he found another one.

T. rex nearly ended up with a very different name. Back in 1892, a scientist called Edward Drinker Cope had already named some of its bones Manospondylus gigas. That means “giant porous vertebra”. A vertebra is one of the bones in the backbone. Cope thought the bones came from a relative of Triceratops. He had guessed completely wrong.

Scientists later realised that both names belonged to the same species, or kind of animal. Normally, the first name given to a species is the one that counts. But so many scientists already used Tyrannosaurus rex that the older name was quietly dropped.

When and where T. rex lived

T. rex lived between about 68 and 66 million years ago. That is the very end of the Cretaceous Period, the last part of the age of dinosaurs.

Its fossils come from western North America, in the USA and Canada. The first skeleton was found in Wyoming, and the famous skeleton called SUE came from South Dakota.

The land there was warm and humid. T. rex shared it with plant-eaters such as Triceratops and Edmontosaurus, a duck-billed dinosaur. We know it fed on both, because its tooth marks have been found on their bones.

Triceratops was no small snack. At about 9 metres (30 feet) long and 13 tonnes, it was roughly twice as long and heavy as an African elephant. A grown Triceratops outweighed a grown T. rex.

Here is a way to picture how long ago that was. Allosaurus, a big hunter from the Jurassic Period, lived about 152 to 145 million years ago. By the time Tyrannosaurus appeared, Allosaurus had been gone for nearly 80 million years. Only 66 million years separate the last Tyrannosaurus from us today. So you live closer in time to Tyrannosaurus than Tyrannosaurus did to Allosaurus.

How big was T. rex?

T. rex grew to about 12 metres (39 feet) long from nose to tail. That is about as long as two and a half African elephants standing in a line.

Its hips were 3.5 to 4 metres (12 to 13 feet) off the ground, so a tall grown-up would only reach about halfway up its leg.

Most adults weighed between 5 and 7 tonnes (11,000 to 15,400 pounds). A big one weighed about as much as an African elephant, the heaviest land animal alive today.

The head alone was enormous. The biggest skulls were more than 1.5 metres (5 feet) long, which is longer than most people are tall.

The largest skeletons found so far are SUE and one called Scotty. Together they hold the Guinness World Record for the biggest known Tyrannosaurus. In life, each weighed more than 8 tonnes and was almost 13 metres (43 feet) long.

Sizes varied, though, and most were probably smaller than these two giants. How did it compare with other big meat-eaters? The table below sets it beside three famous hunters from different times.

Dinosaur	When it lived	Length	Weight
Tyrannosaurus rex	Late Cretaceous, 68–66 million years ago	12–13 m (39–43 ft)	5–7 tonnes; the largest over 8 tonnes
Spinosaurus	Late Cretaceous, from about 95 million years ago	14 m (46 ft)	about 7.4 tonnes
Giganotosaurus	Cretaceous, before T. rex	about 13 m (43 ft)	about 7.2 tonnes
Allosaurus	Late Jurassic, 152–145 million years ago	9.7 m (32 ft)	about 2.7 tonnes

Spinosaurus is the longest meat-eating dinosaur known. It had a tall sail or hump along its back, and some scientists think it hunted fish in water, although others disagree.

Giganotosaurus came from what is now Argentina, in South America, and it may have been about the same size as T. rex. Its size is hard to pin down, though, because only broken pieces of its skeleton have been found. T. rex is known from many good skeletons, so its size is far more certain.

Allosaurus was much smaller. At 2.7 tonnes, it weighed less than half as much as a big T. rex.

Teeth and the strongest bite

T. rex had about 60 teeth in its jaws. The biggest were up to 20 centimetres (8 inches) long, about as long as a new pencil. Each tooth was pointed, with saw-like edges, a bit like a bread knife.

Its bite was the strongest of any known land animal. It was three to five times more powerful than the bite of a lion.

The American Museum of Natural History puts the force at about 7,800 pounds (3,500 kg), like three cars pressing down through its teeth.

That bite smashed bone. Pieces of crunched bone have even been found in its fossilised dung. Scientists call fossil dung a coprolite, and it can show what an animal ate millions of years ago.

Did it hunt, or did it only eat animals that were already dead? People have argued about this for a long time. The Natural History Museum in London says Tyrannosaurus probably did both. It hunted living prey, and it also scavenged dead bodies when it found them.

Some of their bones even carry bite marks from other tyrannosaurs. So they certainly fought each other, although nobody knows whether they fought over food or for other reasons.

Why were its arms so small?

T. rex had tiny arms compared with the rest of its body. They were small, but they were not weak. The arm bones were attached to strong muscles.

Nobody knows for certain what the arms were for. Scientists have a few ideas, and more than one of them may be right.

• Getting up. After a fall, a heavy adult may have used its strong arms to push itself off the ground.
• Feeding. Young ones had arms that were bigger for their size, so they may have used them to grab food.
• Holding on. A male may have used his arms to hold on to a female while they mated.

The answer may be all three. As young tyrannosaurs grew up, their huge jaws could do the catching, and the arms may have mattered less and less.

Scientists are still studying real arms for clues. In 2016, one of SUE’s arms travelled to Argonne National Laboratory in Illinois. There it had micro-CT scans, which are very detailed X-ray pictures of the inside of a bone.

How fast could T. rex move?

Films often show a T. rex racing after a speeding car. The real animal was far slower.

The Natural History Museum estimates that an adult had a top speed of around 22 kilometres per hour (14 mph). That is roughly how fast a fit person can sprint. A car driving through town would leave it behind.

That was its fastest, not how it usually moved. At that pace, the museum says, a tumble now and then would have been likely. Being able to get up again would have mattered a great deal.

Younger animals may have moved even faster than adults. Remember, though, that every speed is an estimate. Nobody can time a fossil. Scientists work it out from the size of the legs and the strength of the bones and muscles, and different studies reach different answers.

Eyes, nose and brain

T. rex had eyes the size of oranges. The American Museum of Natural History says they were the largest eyes of any land animal.

Its eyes faced forward, like the eyes of hawks and eagles. They were also set wide apart. This gave it excellent depth perception, which means it could judge how far away things were.

The eyes sat high on its head, which helped it see a long way. Birds and crocodiles, its closest living relatives, can see ultraviolet light. Scientists therefore think it probably saw a wider range of colours than we do.

Its nose was even better. A large part of its brain was used for smelling. Scientists know this from the space inside fossil skulls, which shows the shape of the brain that once filled it.

A strong nose would have helped it find food from far away, whether that was a living animal or one that had already died.

Growing up: the teenage growth spurt

T. rex grew fast, especially as a teenager. SUE had a growth spurt in its teens, gaining as much as 2 kilograms (4.5 pounds) a day. That is like adding two big bags of sugar to its weight every single day.

At that rate, it would gain more than 700 kilograms in a year. That is heavier than most horses.

SUE reached full size at about 19 years old. It died at about 28. The Field Museum says that is near the upper end of the life expectancy for Tyrannosaurus.

So a long-lived Tyrannosaurus spent about two-thirds of its life growing, but a person grows for only about a quarter of theirs.

How can anyone tell the age of a dinosaur? Bones grow in layers, a bit like the rings inside a tree trunk. Counting the layers gives scientists an estimate of how old the animal was when it died.

Scales or feathers?

Many theropods, the group T. rex belonged to, had feathers. So people often wonder whether Tyrannosaurus was feathered too. So far, the answer is scales.

There is no direct evidence that Tyrannosaurus had feathers. Patches of fossil skin from it and its close relatives have been found, and they show scales. Scales are small, tough plates, like the skin on a lizard or on a bird’s legs.

Scientists think feathers may have disappeared as tyrannosaurs got bigger, because a huge body holds on to its heat well. So a giant living somewhere warm did not need a fluffy coat.

A different tyrannosaur, Yutyrannus, did have feathers, but it lived in a cold climate, where a feathery coat would have kept it warm.

One question is still open. No skin has yet been found from the back of a T. rex. If it had any feathers at all, the Natural History Museum says, that is where they would have been.

Famous T. rex skeletons

Here are some of the most important T. rex finds and events, in date order.

Year	What happened
1892	Edward Drinker Cope names some bones Manospondylus gigas. They later turn out to belong to T. rex.
1900	Barnum Brown finds the first known T. rex skeleton, in Wyoming.
1902	Brown finds a second skeleton.
1905	Henry Fairfield Osborn names the dinosaur Tyrannosaurus rex.
1990	Sue Hendrickson finds SUE near the town of Faith, South Dakota.
1997	The Field Museum buys SUE at auction for $8.4 million.
2000	SUE goes on show in Chicago on 17 May.
2016	One of SUE’s arms is scanned at Argonne National Laboratory.
2025	A study in the journal Nature argues that Nanotyrannus was a separate dinosaur.

SUE is probably the best-known T. rex skeleton in the world. It was found in 1990 by Sue Hendrickson and is named after her. It took six people 17 days to dig the bones out of the ground.

The skeleton is more than 12 metres (40 feet) long and 4 metres (13 feet) tall at the hip. The Field Museum calls it the physically largest of the more than 30 skeletons known. It says SUE is around 90 per cent complete, with 250 of the roughly 380 known bones.

In 1997 the museum paid $8.4 million for SUE, the most money ever paid for a fossil at that time. Getting the bones ready for display took more than 30,000 hours of work. SUE went on show on 17 May 2000.

SUE’s bones hold surprises. There is a wishbone, the same forked bone a chicken has. There is also a set of rib-like bones across the belly, called gastralia. Holes in the lower jaw were probably caused by an infection.

Nobody knows whether SUE was male or female. Fossil bones rarely give that away, so this guide calls SUE “it”.

Scotty is the other giant in the record books, sharing the Guinness World Record for the biggest known Tyrannosaurus with SUE.

New discoveries: the Nanotyrannus debate

For many years, scientists argued about some smaller tyrannosaur fossils found in the same part of North America. Some said they were young T. rex. Others said they belonged to a separate, smaller dinosaur called Nanotyrannus.

On 30 October 2025, two palaeontologists published a big new study in the journal Nature. They were Lindsay Zanno and James Napoli. They described a very well-preserved skeleton from rocks called the Hell Creek Formation.

Its age was the clue. The animal had almost stopped growing. If it was nearly grown up, it could not be a young T. rex.

Zanno and Napoli concluded that Nanotyrannus was a real, separate dinosaur. It sits outside Tyrannosauridae, the family of giant tyrannosaurs that includes T. rex. They also found two species of it. One was Nanotyrannus lancensis, and the other was new, so they named it Nanotyrannus lethaeus.

This means at least two different kinds of tyrannosaur lived side by side in the last million years before the extinction. The result also changes the story of how young tyrannosaurs grew up. Dozens of older ideas about young T. rex will need checking again.

The debate is not quite over. Thomas Carr is a palaeontologist at Carthage College in the USA. He has said that being fully grown does not, on its own, prove that a fossil is a separate species. He has also said that more small T. rex fossils are needed to tell growth apart from evolution, the slow change of living things over many generations.

There is one more thing to know. Other species of Tyrannosaurus have been named by some scientists. The Natural History Museum says none of them is widely accepted, so for now T. rex is the only one.

How T. rex died out

T. rex was one of the very last dinosaurs. About 66 million years ago, a huge asteroid, a rock from space, crashed into Earth.

The crash caused a mass extinction. That is when a very large number of kinds of living thing die out in a short time. Scientists count it among the greatest disasters in the history of life on Earth.

Tyrannosaurus and Triceratops both vanished. So did the giant long-necked titanosaurs. They were sauropods, the same group as Brontosaurus, and they were among the last sauropods left when the asteroid hit.

Not every dinosaur disappeared, though. Birds come from the same family tree. The Natural History Museum even calls the pigeon a distant relative of T. rex.

That is why scientists say the asteroid wiped out the non-avian dinosaurs. The word non-avian simply means “not birds”. You can read about the whole age of dinosaurs in our dinosaur facts for kids.

Three things people get wrong

1. T. rex did not live in the Jurassic. Films with Jurassic in the title made it famous, but it lived 68 to 66 million years ago, in the Late Cretaceous. The Jurassic Period ended about 145 million years ago, when Allosaurus was still alive. Nearly 80 million years separate Allosaurus from Tyrannosaurus, more than the 66 million years between Tyrannosaurus and you.
2. Standing still would not have hidden you. In the film Jurassic Park, a character claims the dinosaur cannot see you if you keep still. The real animal had huge eyes that faced forward and were set wide apart, giving it excellent depth perception. It also had a superb sense of smell, so keeping still would not have kept you hidden.
3. T. rex was not the longest meat-eating dinosaur. Spinosaurus, at about 14 metres (46 feet), was longer, and Giganotosaurus was about the same size. What set Tyrannosaurus apart was its bite, the strongest of any known land animal.

Frequently asked questions

What does Tyrannosaurus rex mean?

Tyrannosaurus rex means “tyrant lizard king”. Henry Fairfield Osborn gave the dinosaur that name in 1905, after Barnum Brown found the first skeletons in 1900 and 1902.

How big was a T. rex?

A fully grown Tyrannosaurus rex was about 12 metres (39 feet) long and 3.5 to 4 metres tall at the hips. Most adults weighed 5 to 7 tonnes, and the largest skeletons, SUE and Scotty, came from animals of more than 8 tonnes.

When did T. rex live?

Tyrannosaurus rex lived about 68 to 66 million years ago, at the very end of the Cretaceous Period, in what is now the USA and Canada. The Cretaceous came after the Jurassic, so it was not a Jurassic dinosaur.

How fast could a T. rex run?

The Natural History Museum in London estimates that an adult Tyrannosaurus rex had a top speed of around 22 kilometres per hour (14 mph). Younger animals may have moved faster, and every speed worked out for a fossil animal is an estimate.

What were T. rex arms used for?

Scientists do not know for certain how Tyrannosaurus rex used its small but muscular arms. The main ideas are pushing up off the ground after a fall, grabbing food when young, and holding on to a mate.

Did T. rex have feathers?

Fossil skin from Tyrannosaurus rex and its close relatives shows scales, and there is no direct evidence of feathers. Skin from its back has not been found, so a few feathers there cannot be ruled out.

Is Nanotyrannus a young T. rex?

A study published in the journal Nature on 30 October 2025 found that Nanotyrannus was a separate, smaller tyrannosaur, not a young Tyrannosaurus rex. Some palaeontologists still question parts of that conclusion.

Sources

• Natural History Museum: Dino Directory, Tyrannosaurus — the name and its meaning, Manospondylus, Barnum Brown’s 1900 and 1902 finds, Osborn (1905), dates and range, length, height, weight, SUE and Scotty, teeth, bite, sense of smell, the arm theories, top speed, and scales and feathers
• Natural History Museum: What was the biggest dinosaur? — the sizes of Spinosaurus, Giganotosaurus, Tyrannosaurus and Triceratops, comparisons with the African elephant, titanosaurs and the asteroid impact 66 million years ago
• Natural History Museum: Dino Directory, Allosaurus — the length, weight and Late Jurassic dates of Allosaurus
• Field Museum: SUE the T. rex — SUE’s discovery, size, completeness, age, growth spurt, wishbone and gastralia, jaw infection, the 1997 auction, the 2000 unveiling, the 2016 arm scans and the count of known skeletons
• American Museum of Natural History: How superior senses helped T. rex hunt — eye size, forward-facing eyes and depth perception, colour vision, the sense of smell and bite force
• Zanno and Napoli (2025), Nature: Nanotyrannus and Tyrannosaurus coexisted at the close of the Cretaceous — the October 2025 study showing Nanotyrannus is a separate dinosaur with two species, and T. rex as one of the last dinosaurs before the mass extinction