Was T. rex a hunter or a scavenger? Scientists have argued over whether T. rex hunted its food or mostly ate animals that were already dead, and the evidence comes from several directions. Here are the main lines. A healed bite wound in a plant-eater is read as a probable sign of predatory behavior. The animal lived long enough after the attack for the bone to heal. Failed attacks count as evidence too: prey that got away with a wound that later healed show that tyrannosaurs hunted live animals, not only dead ones. T. rex was a top predator in its world, and it ate large plant-eaters with thick bones, such as horned and duck-billed dinosaurs.

Eyesight is part of the argument, and it was tested with a careful experiment. In 2006 Kent Stevens of the University of Oregon built models of dinosaur faces to test how well T. rex could see. 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. Over millions of years the T. rex snout grew narrower and its eyeballs bigger, which cleared its view straight ahead. The far point of T. rex vision may have been about 6 kilometers, compared with 1.6 kilometers for a person.

The jaws tell a story as well. As of May 2017, scientists put the bite of T. rex at about 8,000 pounds of force; it bit with more than twice the force of the largest living crocodiles, which bite with about 3,700 pounds. Bite force alone does not tell how well an animal can crush bone, however. Tooth pressure matters more, and T. rex tooth tips reached 431,000 pounds per square inch. Researchers built 3-D computer models of T. rex jaw muscles from what they measured on living crocodiles. The bone-crushing bite let T. rex eat bones and marrow that smaller meat-eating dinosaurs could not use; T. rex teeth were thick and blunt rather than thin flat blades.

Fossil bones can mislead. Holes in the lower jaw of Sue, the famous skeleton at the Field Museum in Chicago, were once thought to be bite marks from another T. rex, but are now thought to be signs of disease. Sue was found in South Dakota in 1990 and is named after Sue Hendrickson, who found the skeleton; Sue's bones show that she was sick and hurt during her life, and scientists do not know if Sue was a girl or a boy. As of November 2026, Sue is one of the most complete T. rex skeletons ever found, about 90 percent complete.

Weight is hard to know, because nobody knows how plump a living T. rex was, so researchers built weight models that range from severely undernourished to overly obese. A typical adult T. rex probably weighed between 5,000 and 7,000 kilograms, and estimates for the length of the biggest run from about 40 to 46 feet. T. rex grew from about 1 ton to about 6 tons in roughly four years, and it gained about 70 percent of its adult weight in that teenage spurt. The teenage growth of T. rex was like that of an African elephant, but elephants live far longer. Big bones lose their early growth rings as the marrow cavity widens, so scientists read the rings in ribs, shin and hip bones instead.

What T. rex looked like on the outside is also a question of evidence, and here the picture has changed more than once. Preserved skin patches from T. rex and relatives such as Albertosaurus, Daspletosaurus, Gorgosaurus and Tarbosaurus 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 tyrannosaur relative, was about 9 metres long and 1,400 kilograms and lived in a colder climate than T. rex, which may be why it had a feathery coat. A 2023 study argued that tyrannosaurs and other meat-eating theropods had scaly, lizard-like lips covering their teeth, overturning the usual picture of bare teeth.

Speed and arms remain open questions. Scientists think T. rex was not very fast, perhaps 10 to 20 miles an hour at its top speed, and some scientists think an adult T. rex could not run well, and that younger and smaller ones may have been faster. T. rex had very small arms for its big body, but the arms were very strong, and scientists still debate what T. rex used them 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. A giant asteroid hit Earth about 66 million years ago, and T. rex and the other big dinosaurs died out.

Words to know

• scavenger: eats dead animals
• predatory: hunting living prey
• binocular: using both eyes