A group of living things
Dinosaurs
Dinosauria
Birds are living dinosaurs.
Its members' last common ancestor lived about 235 million years ago.
You and dinosaurs last shared an ancestor about 320 million years ago (on 4 December, if life's history were one year).
Every bird pecking in your garden is a living dinosaur. It is wrong to say dinosaurs are extinct. Scientists split them into extinct non-bird dinosaurs and living dinosaurs, the birds. About 66 million years ago a giant space rock about 10 kilometres wide hit Earth. Huge animals like Tyrannosaurus and Triceratops died out. Only small, feathered, bird-like dinosaurs survived.
Extinct dinosaurs held their legs straight under the body, not spread out sideways. Tyrannosaurus walked on two strong hind legs with tiny arms, huge toothed jaws and a long tail for balance. Triceratops walked on four thick legs, with three horns and a wide bony frill behind its head. The biggest long-necked dinosaurs grew to about 35 to 40 metres long and about 60 to 80 tonnes, as long as a bus queue and as heavy as about 10 elephants. The smallest well-known extinct dinosaurs were a little bigger than a chicken. The extinct ones lived only on land, on every continent including Antarctica. Outside the group, their close living relatives are crocodiles.
Flying reptiles and swimming sea reptiles were not dinosaurs, but separate reptile groups. Different dinosaurs also lived at very different times. Stegosaurus died out about 80 million years before Tyrannosaurus appeared.
Eggs in nurseries
Dinosaurs laid hard-shelled eggs in nests made in mud or sand. Some nested together in large groups. Eggs are now known from more than 200 places around the world.
Ginger dinosaur with stripes
Fossil colours show one small dinosaur was ginger with a ginger-and-white striped tail. Another had a dark grey body, black-and-white wings and a red head crest.
Only three at first
The word dinosaur was made up in 1842 for just three dinosaurs known then. It means fearfully great reptiles.