English présentation dinosaursPresentation Transcript
Key points Are they older than we thought ? What causes their expansion ?
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
Where the footprints were discovered?
In Poland, in a 250 million years old rock ie : 2 million years after a mass extinction
What kind of creature it was ?
Caracteristics criteria :
size of a domestic cat
walked on 4 legs
A new discovery => a re-interpretation of dinosaurs's history
Dinosaurs emerged 18 million years before than we thought
The mass extinction has wiped out predators of dinosaurs
Why does dinosaurs survived to the crisis ?
Maybe with a lucky break !
90% of species have disapeared : it needed 10 million years to life to recover
Mammals and dinosaurs have both survived to a mass extinction before their expansion