Dinosaur remains were first found in rocks dating back 250 million years, at the start of the Triassic period, and were extinct at the end of the Cretaceous, about 65 million years ago. That is a very long time, isn’t it? And not all dinosaurs we know about lived all that time – for example, a T Rex and a Stegosaurus did not exist at the same time.
Like Isabel said, dinosaurs lived millions of years ago! All we know about their life styles is through studying their bones and fossils and trying to put different pieces of information together. When it comes to their lifespans we think that they lived for about 75-300 years!