The first question about T. rex is the simplest, and it has no single answer. 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 in 1991, is the largest T. rex known so far, and it is also the oldest, having seemingly lived to its early 30s. Scotty beat Sue's weight estimate by only about 5 percent, which lies within the error of weight guesses for extinct animals, so a record in this field is a fragile thing.
Nobody timed the animal, so its age comes from the rocks around its bones. Hell Creek ages come from volcanic ash: researchers recalibrated the argon-argon dating method and then dated ash collected in the Hell Creek area of Montana. In 2008 the recalibrated method gave 65.95 million years ago as the best date for the end of the Cretaceous, and the date of the impact came out the same, within error limits, as the date of the extinction, precise to within 11,000 years. As of November 2026, scientists link the Yucatan impact crater to an extinction in which more than 50 percent of Earth's species, including the dinosaurs, died out, and they still debate the crater's exact size. Sue lived about 67 million years ago, and T. rex lived near the end of the time of the dinosaurs.
T. rex was the end of a long story, and early in that story tyrannosaurs were not top predators: they hunted in the shadows of older meat-eating lines such as the allosaurs. Moros, an early tyrannosaur, lived about 96 million years ago in what is now Utah and stood only three or four feet tall at the hip, about the size of a modern mule deer. The discovery of Moros narrowed a 70-million-year gap in the fossil record of tyrant dinosaurs in North America. Qianzhousaurus, a long-snouted tyrannosaur nicknamed Pinocchio rex, with Alioramus shows that long-snouted tyrannosaurids were widely distributed in Asia and probably hunted different prey from larger, deep-snouted kin. Birds are modern-day dinosaurs, and a pigeon is a distant relative of T. rex.
The famous growth curve comes from a method as much as a discovery. The 2004 study looked at more than 60 bones from 20 tyrannosaur specimens that died between ages 2 and 28, counting rings in ribs, shin bones and hip bones, which stay solid and so keep every ring; Sue's solid ribs gave the team the idea. Researchers checked the ring method against modern alligators and lizards, whose bone rings form in a similar way, and they estimated how heavy each dinosaur was by measuring the distance around its thigh bone. The result was that T. rex grew from about 1 ton to about 6 tons in roughly four years, and it stopped growing at about age 20, spending about two-thirds of its life growing. The teenage growth of T. rex was like that of an African elephant, but elephants live far longer.
Growth studies rest on the idea that the youngsters in the sample really were young T. rex, and in 2025 that assumption was challenged. As of October 2025, a study in Nature found that Nanotyrannus, once thought to be a juvenile T. rex, was a distinct genus. The debate hung on one question: if Jane and similar skeletons were juvenile T. rex, Nanotyrannus was not a valid species; if not, two tyrannosaur species lived together at the end of the Cretaceous. The result means that growth studies that used Nanotyrannus specimens as stand-ins for teenage T. rex may need a second look, and a bone growth-ring study of the Jane specimen had put her at 11 to 13 years old and about 21 feet long. Another 2025 study in Nature suggested that at least two other kinds of predatory dinosaur may have lived alongside Tyrannosaurus within a million years of the end of the Cretaceous.
The count of species is a second argument. In February 2022 a study argued that T. rex fossils form three species and named two new ones, T. regina and T. imperator. Many leading T. rex experts were not convinced by the three-species study, and critics said the variation among T. rex fossils could come from age, sex or normal individual differences instead of separate species. Over millions of years the T. rex snout grew narrower and its eyeballs bigger, which cleared its view straight ahead.
The bite of T. rex is where the animal departs most from other reptiles. As of May 2017, scientists put the bite at about 8,000 pounds of force, more than twice that of the largest living crocodiles, which bite with about 3,700 pounds, but bite force alone does not tell how well an animal can crush bone: tooth pressure matters more, and T. rex tooth tips reached 431,000 pounds per square inch. T. rex is unique among reptiles in crushing bone like wolves and hyenas do, but without teeth that fit together tightly. Its teeth were thick and blunt, not thin flat blades like those of most other meat-eating dinosaurs. Pieces of bone turn up in fossil T. rex dung, which shows it swallowed the bone it crunched, and the bone-crushing bite let it eat bones and marrow that smaller meat-eating dinosaurs could not use.
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. Jack Horner argued that T. rex could have been a scavenger, pointing to the large smell centres in its brain. In 2006 Kent Stevens of the University of Oregon built models of dinosaur faces to test how well T. rex could see, and the work found that T. rex had a binocular range of 55 degrees, wider than a modern hawk's. One study suggests the vision of T. rex was too good for a pure scavenger, which supports the idea that it was a hunter. A healed bite wound in a plant-eater is read as a probable sign of predatory behavior, because the animal lived long enough for the bone to heal, and failed attacks count as evidence too.
Single skeletons carry the details. Sue was found in South Dakota in 1990 and is named after Sue Hendrickson, who found the skeleton; 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 it. As of November 2026, Sue is one of the most complete T. rex skeletons ever found, about 90 percent complete. Holes in Sue's lower jaw were once thought to be bite marks from another T. rex, but a scientific paper argued that they match a parasite infection that today harms birds, called trichomonosis. 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.
Weight and speed are numbers nobody can watch. Because nobody knows how plump a living T. rex was, researchers built weight models that range from severely undernourished to overly obese. A 2011 mass study built digital models of five T. rex skeletons, including Sue, from laser scans accurate to less than half an inch for skeletons up to 40 feet long, and as of November 2026 those models put Sue at over nine tons, more than older guesses made with scale models, which can magnify even minor errors. 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.
Finally, the picture of the living animal keeps changing. 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. 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 estimates have changed too: older models allowed 11 to 33 miles an hour, while a 2017 model put the likely top near 12 miles an hour, and it found T. rex was typically restricted to a brisk walk. Protein was recovered from soft tissue in a 68-million-year-old T. rex bone, and the method was first tried on modern ostrich.
Words to know
- genus: related animal group
- Cretaceous: last dinosaur age
- scavenger: eats dead animals
- trichomonosis: bird parasite illness
