Dinosaurs belonged to a group of reptiles that included birds, crocodiles and other prehistoric animals such as pterosaurs (flying reptiles). All these animals are called 'archosaurs' or 'ruling reptiles'. Archosaurs first appeared on earth about 250 million years ago.
Dinosaurs were animals that lived in the Mesozoic era between 230 and 65 million years ago. All dinosaurs lived on land, had four limbs, walked on two or four legs and breathed air. Some ate plants, others were fearsome carnivores.
Like other reptiles, dinosaurs had tough scaly skin, with many dinosaurs having great armour plates and shields to fend off predatory dinosaurs. Some smaller species however, sometimes had a soft feathery down, similar to ducks.