Dinosaurs The word "dinosaur" comes from the Greek language and means "terrible lizard".Dinosaurs lived on our planet a very long time ago. The oldest known dinosaur is Eoraptor, a meat-eater that lived 228 million years ago. People believe that dinosaurs lived on the Earth until around 66 million years ago. Some dinosaurs ate meat and others ate plants. Most dinosaurs hatched from eggs, and they could not fly or live in water. Some dinosaurs walked on two legs, while others walked on all four legs. Some had homs and spikes, others had thick bumpy skin, and some even had feathers. The biggest dinosaurs were over 30 metres long and about 20 metres tall. The largest dinosaur was the sauropod. The smallest dinosaurs were the size of a chicken.