The age of the dinosaurs was the Mesozoic Era, which had three periods: the Triassic, the Jurassic and the Cretaceous. The Triassic Period began about 252 million years ago, when all the land was joined in one huge land mass called Pangaea. Dinosaurs first evolved in the Triassic but did not become very varied until the Jurassic, after a mass extinction at the end of the Triassic. As of November 2026, the Jurassic Period began about 201 million years ago, when the Triassic Period ended. As of November 2026, the Cretaceous Period ended about 66 million years ago, with the mass extinction that closed the age of the dinosaurs. Dinosaurs lasted well over 100 million years on land before the end of the Cretaceous.

Scientists learn about dinosaurs from two kinds of fossils: body fossils such as bones and teeth, and trace fossils such as footprints. Dinosaur bones are dug up with the rock around them, wrapped in protective plaster jackets and taken to a laboratory, where preparators work on them. Carbon dating only works on things from the past 50,000 years or so. That is far too recent for dinosaur fossils. Fossils in sedimentary rock are often given an approximate age by bracketing. Scientists date volcanic (igneous) layers above and below the fossil bed. The fossils must fall between those two dates.

As of November 2026, Sinosauropteryx was the first non-avian dinosaur found with feather-like structures on its body. Scientists can work out the colour of some fossil feathers. They study tiny pigment structures preserved in them. As of November 2026, pigment traces preserved in the fossil feathers of Sinosauropteryx indicate that it was probably reddish-brown and ginger in colour, with a striped, banded tail. Microraptor was a tiny feathered dinosaur about the size of a crow. Its feathers were probably black and shiny. Velociraptor had feathers but could not fly.

As of November 2026, in big weight-bearing dinosaur bones, some of the growth rings laid down early in life are erased as the marrow cavity widens. So scientists look to smaller bones that keep their rings to read how fast the animal grew. As of November 2026, a 2004 study of fossil bones from Tyrannosaurus rex found that from about age 14 it entered a four-year growth spurt. It gained, on average, more than 2 kilograms (about 4 to 5 pounds) a day. As of November 2026, scientists have debated whether Torosaurus is just the fully grown form of Triceratops. A 2012 study of skulls concluded that they were different species.

Sue, a Tyrannosaurus rex skeleton in Chicago, is about 13 feet tall at the hip. It is more than 40 feet long. Tyrannosaurus had about 60 big, sharp teeth. As of November 2026, Tyrannosaurus had the strongest bite of any known land animal. T. rex had a good sense of smell, and a large part of its brain handled smells. Some early tyrannosaur relatives were small predators. Tyrannosaurs existed for about a hundred million years before T. rex appeared. As of November 2026, T. rex lived in North America late in the Cretaceous, about 68 to 66 million years ago.

Sauropods such as Diplodocus and Brachiosaurus were huge four-legged plant-eaters with long necks and long tails. Casts of the Diplodocus skeleton nicknamed Dippy, found in Wyoming, were sent to museums in other countries. As of November 2026, Patagotitan, a titanosaur, is one of the largest land animals that has ever lived. As of November 2026, Patagotitan was probably about 120 feet (37 metres) long. But no complete skeleton is known, so its exact length is uncertain. Some of the biggest dinosaurs, such as Argentinosaurus, are known only from very incomplete fossils, so their sizes are estimates.

The word Dinosauria was made up in the early 1840s by Richard Owen, from three British fossils: Megalosaurus, Iguanodon and Hylaeosaurus. The first Iguanodon fossils, found in southern England in 1822, were teeth that scientists first thought belonged to a giant iguana. As of November 2026, Megalosaurus is counted as the first dinosaur to be formally named. In 1824 William Buckland gave it that name, meaning great lizard, in a scientific article. The first Archaeopteryx fossil, found in Germany in 1861, was a surprise because no birds were known from so far back. Scientists are still debating whether Archaeopteryx could truly fly or only glide.

In 1980 the scientists Luis and Walter Alvarez proposed that a large asteroid hit Earth and ended the dinosaurs. Rocks laid down at the end of the Cretaceous hold a thin clay layer with a lot of iridium, a metal that is rare at Earth's surface but common in asteroids. The impact sent dust and soot into the air, which cut down the sunlight reaching Earth's surface and slowed plant growth. As of November 2026, the asteroid that hit Earth about 66 million years ago is estimated to have been roughly 10 to 15 kilometres wide (about 6 to 9 miles). That is much smaller than the crater it left. As of November 2026, the crater, called Chicxulub, is more than 90 miles (150 kilometres) across.

Words to know

• bracketing: dating between layers
• igneous: cooled lava
• pigment: natural colour
• marrow: bone center