Tyrannosaurus Rex

Aside from being one of the largest of the known carnivorous dinosaurs, *Tyrannosaurus rex* — *T. rex*, for short — is the dinosaur that has arguably received the most media exposure. It had a

starring role in the "Jurassic Park" movies and has a renowned exhibit at the American Museum of Natural History in New York City.

The name *Tyrannosaurus rex* means "king of the tyrant lizards": "tyranno" means tyrant in Greek; "saurus" means lizard in Greek, and "rex" means "king" in Latin. In 1905, Henry Fairfield Osborn, president of the American Museum of Natural History at the time, named *Tyrannosaurus rex*.

*T. rex* was a member of the Tyrannosauroidea family of huge predatory dinosaurs with small arms and two-fingered hands. Aside from *Tyrannosaurs*, other Tyrannosaurid genera include *Albertosaurus*, *Alectrosaurus*, *Alioramus*, *Chingkankousaurus*, *Daspletosaurus*, *Eotyrannus*, *Gorgosaurus*, *Nanotyrannus* (a controversial genus that might, in fact, be an *adolescent T. rex*), *Prodeinodon*, *Tarbosaurus* and *Zhuchengtyrannus*.

*T. rex* fossils are found in western North America, from Alberta to Texas. But it's possible that *T. rex* was an invasive species from Asia, according to a 2016 study published in Scientific Reports. An analysis of *T. rex*'s skeletal features showed that the dinosaur king was more similar to two *Tyrannosaurs* in Asia, *Tarbosaurus* and *Zhuchengtyrannus*, than it was to North American *Tyrannosaurs*, the researchers told Live Science. Perhaps the paleo beast crossed over about 67 million years ago when the seaway between Asia and North America receded, the researchers said.

However, the finding is still preliminary, and other experts maintain that *T. rex* evolved in North America, they said. *T. rex* had strong thighs and a powerful tail, which counterbalanced its large head (Sue's skull is 5 feet, or 1.5 m, long) and allowed it to move quickly. The 2011 study, which also modeled *T. rex*'s muscle distribution and center of mass, suggests the giant could run 10 to 25 mph (17 to 40 km/h), as previous studies had estimated.

Its two-fingered forearms were puny, making it unlikely that *T. rex* could use them to kill or even get a meal to its mouth. However, it's possible that *T. rex* had such tiny arms because of its powerful bite, according to research from Michael Habib, an assistant professor of clinical cell and neurobiology at the University of Southern California and a research associate at the Dinosaur Institute at the Natural History Museum of Los Angeles County.

The king of dinosaurs needed thick neck muscles to hold up its large skull and power its forceful bite. Neck and arms muscles compete for space in the shoulder, and it appears that the neck muscles edged out the arm muscles in *T. rex's* case, according to Habib's research. Moreover, long arms can be broken, are vulnerable to disease, and take energy to maintain, so having short arms may have been beneficial to the king in the long run, Habib's research shows. *T. rex* was a huge carnivore and primarily ate herbivorous dinosaurs, including *Edmontosaurus*and *Triceratops*. The predator acquired its food through scavenging and hunting, grew incredibly fast and ate hundreds of pounds at a time, said University of Kansas paleontologist David Burnham.

"*T. rex* was probably opportunistic and may have fed on carcasses, but that is not a very abundant or consistent food source," Burnham told Live Science. "*T. rex* had a hard life. They had to go out and kill for food when they were hungry."

For many years, the evidence that *T. rex* actually hunted for its meals was circumstantial and included such things as bones with bite marks, teeth near carcasses and foot tracks suggesting pursuits, Burnham said. But in a 2013 study in the journal Proceedings of the National Academy of Science, Burnham and his colleagues unveiled direct evidence of *T. rex*'s predatory nature: a *T. rex* tooth embedded in a duckbill dinosaur's tailbone, which healed over the tooth (meaning the duckbill got away).

"We found the smoking gun!" Burnham said. "With this discovery, we now know the monster in our dreams is real."

*T. rex* was also not above enjoying another *T. rex* for dinner, according to a 2010 analysis published in PLOS ONE of *T. rex* bones with deep gashes created by *T. rex* teeth. However, it's not clear if the cannibalistic dinosaurs fought to the death or merely ate the carcasses of their own kind.

Scientists are unsure whether *T. rex* hunted alone or in packs. In 2014, researchers found dinosaur track marks in the foothills of the Canadian Rockies in British Columbia — out of the seven tracks, three belonged to Tyrannosaurids, most likely *Albertosaurus*, *Gorgosaurus* or *Daspletosaurus*. The study, published in PLOS ONE, suggests that *T. rex*'s relatives, at least, hunted in packs. *T. rex* fossils are found in a variety of rock formations dating to the Maastrichtian age of the upper Cretaceous period, which lasted from 67 million to 65 million years ago, toward the end of the Mesozoic Era. It was among the last of the non-avian dinosaurs to exist prior to the Cretaceous-Paleogene extinction event, which wiped out the dinosaurs.

More mobile than many other land-based dinosaurs, *T. rex* roamed throughout what is now western North America, at the time an island continent identified as Laramidia. More than 50 skeletons of *T. rex* have been unearthed, according to National Geographic. Some of these remains are nearly complete skeletons, and at least one skeleton included soft tissue and proteins. [Image Gallery: The Life of T. Rex]

Fossil hunter Barnum Brown discovered the first partial skeleton of a *T. rex* in the Montana portion of the Hell Creek Formation in 1902. He later sold this specimen to the Carnegie Museum of Natural History in Pittsburgh. Another *T. rex* fossil discovery of his, also from Hell Creek, is on display in the American Museum of Natural History in New York.

In 2007, scientists unearthed what may be a *T. rex*footprint in Hell Creek, and described their discovery in the journal Palaios. If the track did indeed belong to *T. rex*, it would be only the second confirmed *T. rex* footprint ever discovered, the first being a footprint discovered in New Mexico in 1993.

T Rex SkeletonTyrannosaurus as it appears in Jurassic ParkTyrannosaurus BodyTyrannosaurus EyesTyrannosaurus JawsTyrannosaurus Feet