Scientists have discovered dinosaur footprints in Poland that date back 2 million years after the worst mass extinction event 252 million years ago. This suggests that dinosaurs arose much earlier than previously thought, directly as a result of ecological gaps left by the mass extinction. The footprints were from small, cat-sized creatures that walked on four legs and were likely herbivorous. This discovery challenges the view that dinosaurs emerged 15-20 million years after the extinction and provides evidence that the devastation paved the way for dinosaurs to fill empty niches left by destroyed predators.

1. Dinosaurs

2. Key points Are they older than we thought ? What causes their expansion ?

3. These earliest dinosaur -like animals were about the size of domestic cats. They would have weighed two or three pounds (1 to 1.5 kilos) and walked on four legs. But what's really intrigued scientists is that they date from two million years after the worst mass extinction event in the history of the planet. It was a time when volcanic eruptions , sudden global warming and a stagnation of the oceans wiped out more than 90% of all life on Earth. Up until recently scientists thought that dinosaurs emerged 15 to 20 million years after this event. But the new footprints suggest that they arose directly as a result of the devastation , filling a gaping ecological void . Without the mass extinctions there would have been no Dinosaurs. Pallab Ghosh, BBC News, London

6. walked on 4 legs

7. herbivore teeth Prorotodactylus

9. The mass extinction has wiped out predators of dinosaurs

11. 90% of species have disapeared : it needed 10 million years to life to recover

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