A group of living things
Crocodiles and dinosaurs
Archosauria
The ruling reptiles
Its members' last common ancestor lived about 250 million years ago.
You and crocodiles and dinosaurs last shared an ancestor about 320 million years ago (on 4 December, if life's history were one year).
Meet the ruling reptiles. This family splits into two living sides: crocodiles and alligators on one, and dinosaurs on the other. That second side includes birds, so a garden bird is a living dinosaur and a closer cousin to a crocodile than any lizard is.
Non-bird dinosaurs ruled the land for over 170 million years, from animals about a metre long to giants tens of metres long. Today the family still spans from tiny birds that fit in your hand to the biggest crocodiles, up to about 7 metres long, longer than a family car. Those big crocodiles have thick armoured skin, eyes on top of the head, and a long strong tail for swimming.
About 66 million years ago, only birds were left to carry the dinosaur side forward. Now birds live almost everywhere, from cities to deserts and polar regions, while wild crocodiles and alligators mostly live in warm rivers and swamps and must still lay eggs on dry land.
Same breath
In both alligators and birds, air flows one way through the lungs. It is a very efficient way to breathe that scientists think first evolved in their common ancestor.
Flying relatives, not dinosaurs
Pterosaurs flew alongside dinosaurs but were neither dinosaurs nor ancestors of birds. They evolved flight separately from birds.
Nest guards
Many female crocodiles and alligators build large mound nests and fiercely guard their eggs and young. Most parent birds give chicks a lot of care until they are grown.