Dinosaurs were reptiles that dominated life on land from about 220 million to 65 million years ago, when all of them mysteriously became extinct.
Although modern reptiles walk with bent legs splayed out, dinosaurs had straight legs under their bodies – this meant they could run fast or grow heavy.
Some dinosaurs ran on their back two legs, as birds do. Others had four sturdy legs like an elephant’s.
Dinosaurs are split into two groups according to their hipbones – saurischians had reptile-like hips and ornithischians had bird-like hips.
Saurischians were either swift, two-legged predators called theropods, or hefty four-legged herbivores called sauropods.
Theropods had acute eyesight, fearsome claws and sharp teeth. They included Tyrannosaurus rex, one of the biggest hunting animals to ever live on land – over 15 m long, 5 m tall and weighing more than 7 tonnes.
Sauropods had massive bodies, long tails, and long, snake-like necks.
The sauropod Brachiosaurus was over 23 m long, weighed 80 tonnes and towered 12 m into the air. It was one of the biggest creatures ever to live on land.
Most dinosaurs are known from fossilized bones, but fossilized eggs, footprints and droppings have also been found. In 1913, mummified hadrosaur skin was found.
Some scientists think the dinosaurs died out after a huge meteor struck Earth off Mexico, creating a cloud that blocked the sun’s light and heat.