Dinosaurs were doing better than ever when they were wiped out 65 million years ago, according to new research.
A study of fossils from around the world claims there were at least 245 types of species of dinosaur when they disappeared in the Cretaceous period.
Scientists say they were very varied, from the famous Tyrannosaurus Rex, to hadrosaurs, which had duck-billed jaws filled with teeth for chewing plants.
No-one knows what killed the dinosaurs, but some think it was a huge asteroid.
Dinosaurs first appeared about 230 million years ago, and were all very similar.
By 160 million years ago, they had developed into 40 different genera, or groups of species.
Peter Sheehan, from a museum which took part in the survey, said the way the dinosaurs differed from each other by the Cretaceous period was "absolutely breathtaking".
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