Tyrannosaurus Rex: A Complete Guide to the Most Famous Dinosaur

Tyrannosaurus Rex is the dinosaur every other dinosaur gets compared to. Its name means "tyrant lizard king." It lived during the Late Cretaceous Period, about 68 to 66 million years ago, and was one of the last dinosaurs to walk the Earth before the mass extinction. This guide covers everything reliably known about T-Rex from museum collections and the past three decades of paleontology research — including the things that have changed since you were a kid.

Quick facts#

• Lived: Late Cretaceous, about 68 to 66 million years ago
• Length: 40 feet (12 meters) head to tail
• Height at hip: 12 to 13 feet (3.7 to 4 meters)
• Weight: 9 tons (18,000 pounds) — about the weight of a school bus
• Diet: Carnivore (meat-eater)
• Where found: Western North America — Montana, South Dakota, Wyoming, Alberta
• Bite force: Estimated 12,800 pounds per square inch — the strongest of any known land animal

What T-Rex looked like#

A 40-foot-long, 9-ton predator that walked on two powerful back legs. The head alone was about 5 feet long. The skull held around 60 banana-sized teeth — each serrated like a steak knife, up to 12 inches long including the root. The neck was thick and muscular to support that massive head.

The most famous feature, though, is the tiny front arms. Two-fingered, about 3 feet long total — comically small for an animal that big. Scientists have debated what they were used for since the first T-Rex was named in 1905. The current best answers: gripping struggling prey, helping it stand up after lying down, or aiding in mating positions. They were not vestigial — the bones show they were actively used. They just look strange to us because we expect predator arms to be huge.

What it ate#

Pure carnivore. Big prey: hadrosaurs (duck-billed dinosaurs), Triceratops, Edmontosaurus, sometimes ankylosaurs. Possibly young sauropods. The famous T-Rex vs Triceratops match-up is real — fossils of Triceratops have been found with T-Rex bite marks healed over, meaning the Triceratops survived the attack at least once.

Paleontologists have debated for years whether T-Rex was an active predator or a scavenger. The current consensus from the American Museum of Natural History's dinosaur collection and recent research is that it was probably both — hunting live prey when it could, scavenging carcasses when the opportunity came up, like most large modern predators (lions, hyenas, polar bears all do both).

What's been discovered in the last 20 years#

The image of T-Rex has changed significantly since the 1990s.

Feathers, maybe#

T-Rex was a coelurosaur — a group of dinosaurs that included many feathered species. Direct fossil evidence of T-Rex feathers has not been found (feathers do not preserve well in T-Rex's environment), but related Tyrannosaurus species (Yutyrannus, found in China) had feathers. The current consensus: T-Rex probably had at least some feathers, especially as a juvenile. Adults may have been more scaly. The "naked giant lizard" image from Jurassic Park is likely wrong.

Probably could not run#

The classic T-Rex chasing a Jeep at 50 mph is fiction. Recent biomechanical studies show that T-Rex's leg structure and body weight made running impossible — at 9 tons, falling at speed would have shattered its ribs. The current estimate is a top speed of about 12 to 15 mph, a fast walk. Still fast enough to catch most prey, which also could not run that fast.

Good eyesight#

T-Rex had forward-facing eyes (like predators today) giving it binocular vision with depth perception. Compared to other dinosaurs, the eye sockets were enormous. It saw the world in detail.

Sense of smell#

The olfactory bulb (smell center of the brain) in T-Rex was huge — proportionally larger than in any modern bird. T-Rex could smell carcasses and prey from a distance. This is part of the argument for some scavenging behavior.

Lifespan and growth#

T-Rex grew fast and died young. Adults were about 28 to 30 years old at death. Juveniles grew about 5 pounds per day during their fast-growth years (ages 14 to 18).

Where T-Rex fossils are found#

Western North America — the geology of Montana, South Dakota, Wyoming, and the Hell Creek Formation specifically. The most famous T-Rex specimens:

• "Sue" at the Field Museum in Chicago — the most complete T-Rex skeleton ever found, discovered in 1990 in South Dakota
• "Stan" at the Abu Dhabi Natural History Museum — the second-most complete
• "Trix" at Naturalis in the Netherlands — one of the largest specimens
• "Scotty" at the Royal Saskatchewan Museum — possibly the heaviest specimen on record

For Florida families specifically: there are no T-Rex fossils in Florida. T-Rex lived in the western interior of North America during the Late Cretaceous, when much of present-day Florida was underwater. Florida's prehistoric fossils are from later periods, when marine megafauna like megalodon lived in the warm shallow seas. See our Florida's prehistoric past post for what is found locally.

How scientists know what they know#

Most of what we know about T-Rex comes from the bones — but the methodology has gotten more sophisticated.

• Skeletal anatomy tells us about size, posture, and locomotion
• CT scans of skulls reveal brain structure, sensory organs, and bite forces
• Tooth wear patterns show what it ate and how
• Bone microstructure tells us age at death and growth rate
• Trackways (preserved footprints) confirm walking speeds
• Coprolites (fossilized droppings) sometimes preserved with bone fragments inside — direct evidence of diet

For a broader look at how paleontologists figure out what dinosaurs looked like and behaved, see our how do scientists know what dinosaurs looked like guide.

T-Rex in popular culture vs reality#

The Jurassic Park T-Rex is partly accurate, partly Hollywood. What is right: the size, the general appearance, the binocular vision, the meat-eating diet. What is wrong: it could not run that fast, it likely had at least partial feather coverage, and the "movement-based vision" plot point was made up for the movie (T-Rex had excellent vision regardless of whether prey was moving).

The good news for movie fans: T-Rex was real, and it was just as terrifying as the movies suggest. A 9-ton predator with binocular vision, the strongest bite force in known land animal history, and teeth the size of bananas does not need to run at 50 mph to be scary.

At a Jurassic Petting Zoo Premium event#

Our Premium experience ends with an 8-foot animatronic T-Rex comedy finale — calibrated for the age in the room (younger kids get the comedy version, older kids get the full intensity). It is a chance for kids who have read every T-Rex book to see one at near-life scale in their own backyard or school.

For South Florida families and schools curious about meeting our T-Rex, see the experience page or book a date.

Frequently asked questions#

How big was T-Rex compared to a person?#

A 40-foot T-Rex was about 13 feet tall at the hip. A 6-foot tall adult human comes up to about half the height of T-Rex's leg. Sue at the Field Museum's mounted skeleton looms over visitors at full size.

Was T-Rex the biggest dinosaur?#

No. Several sauropods (long-necked dinosaurs) were much bigger — Argentinosaurus and Patagotitan likely exceeded 100 feet long and weighed 70+ tons. T-Rex was the biggest of the meat-eating dinosaurs in North America, but not the largest dinosaur overall. Spinosaurus and Giganotosaurus were also larger predators by length.

Were there T-Rex in Florida?#

No. T-Rex lived in western North America. Florida's land mass at the time was underwater or vastly different from today. The closest contemporaries in the southeast were different theropod species, but T-Rex specifically is a western North America story.

Why are T-Rex arms so small?#

Best current theories: gripping struggling prey close to the body, helping it stand up after lying down, and possibly courtship. The bones show muscle attachment points, meaning the arms were used for something — they were not just vestigial leftovers. Just smaller than we instinctively expect for a predator that big.

Did T-Rex have feathers?#

Probably some, especially as juveniles. Adults may have been more scaly. Direct fossil evidence of T-Rex feathers has not been found, but closely related species had them, and the consensus among paleontologists has shifted toward feathered T-Rex over the past 15 years.

How fast could T-Rex run?#

It could not run, technically. Top speed estimated at 12 to 15 mph — a fast walk, not a sprint. The Jurassic Park chase scene is not biomechanically possible for an animal that size.

What killed T-Rex?#

The Cretaceous-Paleogene extinction event, about 66 million years ago. An asteroid impact in what is now Mexico's Yucatán Peninsula triggered a global cooling event that ended the dinosaur era. T-Rex was one of the last dinosaur species alive when it happened. Full story in our why did dinosaurs go extinct post.

Bring the science to life#

A T-Rex skeleton at a museum is incredible. Meeting one in your space — even an animatronic baby T-Rex or an 8-foot adult in our Premium show — is a different kind of memory. For South Florida families and schools who have read every T-Rex book and want the real-world capstone, the experience page explains what we do, or book your date directly.