Dinosaurs first appeared between 247 and 240 million years ago. An extinction event wiped them out 65,5 million years ago, except for the avian dinosaurs.

Scientists think the extinction was likely because of an asteroid impact, chemicals from erupting volcanoes, climate change and other factors.

Fossils reveal that some of the more advanced dinosaurs had feathers or featherlike body covering.

• Archaeopteryx was considered the first bird but probably couldn't fly far.
• Pterosaurs - extinct flying reptiles - were not dinosaurs although they were close relatives of dinosaurs. They had hollow bones, relatively large brains and eyes, and skin flaps extended along their arms.

In 1842, palaeontologist Richard Owen coined the term dinosaur. The Greek deinos means "terrible," and sauros means "lizard" or "reptile."

Based on the structure of the hipbones, dinosaurs are classified into two orders:

• Saurischians. These "reptile-hipped" dinosaurs have a pelvis that points forward. They are often long-necked, have large and sharp teeth, long second fingers, and a first finger that point away from the rest of the fingers.
• Ornithischians are beaked herbivores and milder.

Well-known dinosaurs like the Tyrannosaurus rex, Deinonychus and Velociraptor fall into this order. Saurischians are divided into two groups.

• Sauropods are four-legged herbivores. They had long heads, long necks and long tails. Leaf-eating Apatosaurus, Brachiosaurus and Diplodocus fall into this family.
• Theropods are two-legged carnivores. There are some of the most fearsome dinosaurs, including Allosaurus and T. rex.

Ornithischians include horned and frilled Triceratops, spiked Stegosaurus and armoured Ankylosaurus.

They often lived in herds and were prey to the larger species of dinosaurs.

In 2017, a study suggested that this hip-oriented classification was incorrect.

Theropods are likely related to the ornithischian dinosaurs. The theropods and Ornithischia form a newly identified group known as Ornithoscelida. If this is correct, it may explain why both theropods and Ornithischia have feathers, while other dinosaurs don't.