<human>:  When did the dinosaur extinction happen?
<bot>: The extinction occurred at the end of the Cretaceous period, 65 million years ago. It is estimated that the extinction occurred around 66 million years ago. The extinction event is believed to have been caused by a large asteroid or comet impact, which triggered a mass extinction event. The extinction was global, and caused the extinction of many species, including the non-avian dinosaurs, pterosaurs, marine reptiles, and ammonites.