What happened to Dinosaurs?

About 65 million years ago dinosaurs seem to have abruptly died out. We know this because their fossilised remains don't appear in rocks younger than this.
There is evidence that a huge asteroid collided with the Earth around the same time leading scientists to believe that the two events are related.
It is possible that, apart from local damage caused by the explosive nature of such an event, an asteroid impact could have thrown huge amounts debris into the upper atmosphere blocking out the sun causing global temperatures to drop. Dinosaurs, being cold blooded, would have been badly affected by this, possibly enough to prevent them competing for a limited food supply with other warm blooded animals such as mammals.
Another theory suggests that major volcanic activity caused a similar scenario. It's even possible that the outbreak of a major disease caused Dinosaur numbers to fall below the minimum number of fit and healthy animals required to successfully breed.
Whatever the cause it gave mammals a chance, and they took it, becoming the dominant animal type after the extinction event.
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