A T. rex did not slice its food; it crunched it. T. rex teeth were thick and blunt, not thin flat blades like those of most other meat-eating dinosaurs, and an adult had about 60 of them. The biggest teeth, root and all, were about a foot long. As of May 2017, scientists put the bite at about 8,000 pounds of force, and T. rex bit with more than twice the force of the largest living crocodiles, which bite with about 3,700 pounds. That bone-crushing bite let T. rex eat bones and marrow that smaller meat-eating dinosaurs could not use, and pieces of bone turn up in fossil T. rex dung, which shows it swallowed the bone it crunched.

T. rex had a large part of its brain for smell, which helped it find food from far away. Its eyes were sharp as well: the far point of its vision may have been about 6 kilometers, compared with 1.6 kilometers for a person. A 2006 study found that T. rex had a binocular range of 55 degrees, wider than a modern hawk's, so both eyes saw the same space ahead. With a nose and a pair of eyes like these, T. rex was well equipped to be a top predator in its world, and it ate large plant-eaters with thick bones, such as horned and duck-billed dinosaurs.

T. rex had very small arms for its big body, but the arms were very strong, and its back legs were big and strong, with three toes. Scientists still debate what T. rex used its small arms for. Young T. rex had arms closer in proportion to their bodies, so the arms might have helped grab food and may have mattered less as the animals grew. Scientists think T. rex was not very fast, perhaps 10 to 20 miles an hour at its top speed.

T. rex grew very fast when it was a teenager. It grew from about 1 ton to about 6 tons in roughly four years, and it grew fastest between about age 14 and age 18. During that spurt it gained about 70 percent of its adult weight. The teenage growth of T. rex was like that of an African elephant, but elephants live far longer. T. rex stopped growing at about age 20 and spent about two-thirds of its life growing. Scientists count growth rings in bones to tell how old a dinosaur was.

How big was the biggest T. rex? Estimates for the length of the biggest T. rex run from about 40 to 46 feet, and a typical adult probably weighed between 5,000 and 7,000 kilograms. T. rex bodies varied from one animal to the next, with some lankier and some more robust, and most were probably smaller than the record sizes. As of March 2019, a T. rex nicknamed Scotty, found in Canada, is the largest T. rex known so far, and it is also the oldest, having seemingly lived to its early 30s. Scotty was found in 1991 in Saskatchewan, and its bones took about a decade to cut out of hard sandstone. Scotty weighed an estimated 19,400 to 19,600 pounds, which is about 8,800 kilograms.

Sue is a famous T. rex skeleton that you can visit at the Field Museum in Chicago. Sue was found in South Dakota in 1990, and the skeleton is named after Sue Hendrickson, who found it. Digging Sue out of the ground took six people 17 days, and after Sue was bought, 12 museum preparators spent more than 30,000 hours cleaning and preparing the skeleton. Sue lived about 67 million years ago, and Sue's bones show that she was sick and hurt during her life. As of November 2026, Sue is one of the most complete T. rex skeletons ever found, about 90 percent complete.

T. rex lived in a warm, humid, almost subtropical world with lush plants. Preserved skin patches from T. rex and its relatives show small pebbly scales, so as of November 2026 most of T. rex was probably not feathered, though a partial covering is not ruled out. Yutyrannus, a feathered relative, lived in a colder climate, which may be why it had a feathery coat. Henry Fairfield Osborn was the scientist who first named and described T. rex, and Barnum Brown found two early skeletons, in 1900 and 1902. A giant asteroid hit Earth about 66 million years ago, and T. rex and the other big dinosaurs died out, yet birds are modern-day dinosaurs.

Words to know

• marrow: soft bone center
• predator: a hunting animal
• subtropical: warm and wet