Dinosaurs (Dinosauria) were reptiles that lived in past times. The word \"dinosaur\" comes from Greek, meaning \"terrible lizard\". Scientists think dinosaurs first appeared about 230 million years ago. About 65 million years ago, dinosaurs became extinct. Birds are sometimes considered descendants of dinosaurs.
There were many kinds of dinosaurs. Today scientists know about hundreds of different kinds of dinosaurs. Some, called herbivores, ate plants and others, called carnivores, ate meat. The largest dinosaurs were plant-eaters, like Apatosaurus and Brachiosaurus. They were the largest animals to ever walk on dry land.