Dinosaurs have walked the Earth for over 165 million years. Many people believe that dinosaurs became extinct because an asteroid hit the Earth, changing the climate dramatically.

The biggest dinosaurs were over 100 feet long and 50 feet tall. The largest dinosaur is the Sauropod.

The smallest dinosaurs were the size of a chicken and were called mussaurus, or mouse lizard.

Some dinosaurs were carnivores, meat-eaters, and some were herbivores, plant eaters. Some walked on two legs, while others walked on all four legs. Some had horns and spikes, others had thick bumpy skin, and some even had feathers.