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Tyrannosaurus Rex Was the Tyrant Lizard King

Tyrannosaurus rex
Tyrannosaurus rex is probably the most recognized dinosaur in the world and the one that springs to mind when most people hear the word "dinosaur." ullstein bild/Getty Images

Raise your hand if you remember this scene. In "Jurassic Park" (1993), leading man Sam Neill stared down one of prehistory's biggest land predators: Tyrannosaurus rex.

A single line eased the tension. Earlier in the movie, Neill's character said Tyrannosaurus' visual acuity was "based on movement." Stand perfectly still, he claimed, and the carnivore wouldn't even know you were there.

That got computer scientist Kent Stevens thinking.

In 2006, he compared the eye socket orientation of several meat-eating dinos, T. rex included. When you look straight ahead, the area that both eyes can see simultaneously is called your "binocular field of view," or BFoV. The wider your BFoV, the better your depth perception.

How did T. rex measure up? According to Stevens' findings, the dinosaur possessed an impressive BFoV that was up to 55 degrees wide. Not even today's hawks can match this figure.

So far from being visually impaired, as "Jurassic Park" suggested, the evidence tells us Tyrannosaurus rex probably had great depth perception. And that's just one amazing aspect of its natural history we'll explore here.

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Long Live the King

People were going gaga for T. rex long before "Jurassic Park" came out. Paleontologist Henry Fairfield Osborn coined the dinosaur's name in 1905. Derived from Latin and Greek, Tyrannosaurus rex means "tyrant lizard king."

Osborn named the species on the basis of an incomplete skeleton found by the legendary fossil-hunter Barnum Brown at a Montana dig site in 1902.

Two years prior, Brown had discovered another carnivorous dinosaur's remains in eastern Wyoming. Close inspection would prove it belonged to the same species, although Osborn didn't recognize this at first. Nobody's perfect.

Osborn's workplace — the American Museum of Natural History in New York City — eventually mounted one of Brown's T. rex specimens in 1915. Then the film industry stepped in. Stop-motion animator Willis O'Brien brought the beast to life for 1918's "The Ghost of Slumber Mountain," an early dinosaur flick.

T. rex has stayed in the public eye ever since. As science historian Jane Davidson notes, it's the animal that probably springs to mind when most of us hear the word "dinosaur."

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Larger Than Life

Parts of around 50 individual Tyrannosaurus have been found in western North America. These range from isolated backbones to (almost) full skeletons.

Claws-down, the most complete T. rex yet discovered is "Sue." A beautiful find from South Dakota, this celebrity skeleton is now on display at the Chicago Field Museum. Scientists have identified 380 bones that a full-grown Tyrannosaurus would've possessed. Sue contains 250 of these and is about 90 percent complete overall.

Sue's also one of the bigger skeletons on record. T. rex had a maximum hip height of roughly 12 feet (3.6 meters) and could grow to be 40 feet (12.1 meters) in length. The skull alone is over 4 feet (1.2 meters) long in large adults.

Ah, but kings invite challengers. Giganotosaurus, a predatory dinosaur native to South America, may have been just a smidge longer than T. rex, measuring around 41 feet (12.5 meters) from nose to tail.

Then there's the fin-backed weirdo Spinosaurus. Presumably semiaquatic, this African carnivore has gotten a lot of attention from the press in recent years. Estimates based on newfound fossils put its total length at 52.4 feet (16 meters) or so.

Guessing any dinosaur's weight is never an easy task. By one calculation, a full-grown T. rex would've pushed 17,000 pounds (about 7,700 kilograms). At that size, Tyrannosaurus may have been heavier than Giganotosaurus or Spinosaurus, despite the theoretical length disadvantage.

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Coming to America

Sure, T. rex, Giganotosaurus, and Spinosaurus had their differences. But all three belonged to the same group: a huge and diverse array of dinosaurs known as the "theropods."

Tyrannosaurus was the largest — and one of the last — tyrannosauroids. That's a theropod subgroup that first appeared in Eurasia 170 million years ago, during Earth's Jurassic Period. These critters started small; an early species named Kileskus was about the size of an adult human being.

Geologically, T. rex had a brief reign. The fossils this giant left behind range from 68 to 65.5 million years of age. So Tyrannosaurus was around to see the last days of the Cretaceous Period, which ended with a mass extinction event 65.5 million years ago. Birds (i.e., modern theropods) were the only dinosaurs to survive this ordeal.

At some point, the tyrannosauroids entered North America. No T. rex remains have ever been found outside this continent, but a 2016 paper speculates that the species could've originated in Asia and later spread into the New World. In other words, perhaps Tyrannosaurus rex was an invasive species.

t rex
Paleontologists of the Natural History Museum of Los Angeles prepare and assemble the fossil of a 70 percent complete, 66 million-year-old Tyrannosaurus rex nicknamed Thomas, in 2008. This specimen, excavated in Montana between 2003 and 2005, is one of 30 partially complete T. rex fossils worldwide.
GABRIEL BOUYS/AFP/Getty Images

The Asian giant Tarbosaurus battar — another tyrannosaur from the Late Cretaceous — is thought to be one of T. rex's closest known relatives.

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Growing Pains

Some of the T. rex skeletons paleontologists have dug up didn't belong to full-grown animals.

Judging by the bone microstructure evidence, it would've taken a Tyrannosaurus 20 years or so to attain its maximum size. Maturity came with some lifestyle changes. Adult T. rex had thick banana-shaped teeth, rigid skulls and seriously powerful jaw muscles. Those attributes gave the dinosaurs a punishing bite force of nearly 7.1 tons (6.5 metric tons).

Like hyenas, mature Tyrannosaurus were consummate bone-crushers. On the other hand, juvenile T. rex had narrow, blade-like teeth and weaker jaws. So instead of pulverizing bones, the youngsters probably specialized in slicing up meat.

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Feeding Time

Proportionately, adolescent T. rex had longer arms and legs than their parents did.

At about 3 feet (0.9 meters) long, the forelimbs on an adult Tyrannosaurus look rather puny when you take the total body size into account. Nobody knows what their function was. Maybe the appendages were "meat hooks" used to grasp struggling victims. Or maybe they helped the dinosaurs hang on to their partners during sex (cue the light saxophone riff).

The legs have also garnered attention. "Jurassic Park" showed a huge T. rex running after Jeff Goldblum at 45 miles per hour (72.4 kilometers per hour).

Sorry to burst your bubble, but that'd be physically impossible. According to biomechanical research published in 2017, T. rex legs just weren't built for running. Instead, the dinosaur was more of a speed-walker, striding across the prehistoric countryside at up to 12 miles per hour (19.3 kilometers per hour).

On top of being a sharp-eyed predator, Tyrannosaurus had a keen sense of smell — as evidenced by the contours of its brain cavity.

The theropod sure wasn't picky about its meals. Bitemarks attributed to this carnivore have been found on the bones of Triceratops, "duck-billed" plant-eaters called hadrosaurids and even other Tyrannosaurus skeletons.

Yes, friends, the "tyrant lizard king" probably ate its own kind. Cannibalism is nothing new, you know...

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