They stalked the earth around a hundred million years ago and scientists are constantly looking for new dinosaur fossils.
Now, Sir David Attenborough has uncovered the world's biggest known dinosaur for his latest documentary.
The new species was 37 metres long - about the length of four London buses.
He told Newsround he believes there's a very small chance the prehistoric beasts could be brought back from extinction.
But he said that it would be very expensive, and it would be better to concentrate on looking after the animals we already have.
You can watch the first of Sir David's new series 'Attenborough And The Giant Dinosaur' on Sunday 24 January, at 6.30pm on BBC One.