This is what happened in the K-T extinction:
A meteorite, 6km long hit the Gulf of Mexico around 65 million years ago.
Than it caused a global earthquake, after that a shockwave of super heated gas formed that was moving away from impact zone.
Than all the debris (that was in the sky right after impact) fell towards the ground, which heated the earths surface to around 1000 regress Celsius. Also East Asia was the last area to feel the danger.
Lastly all the smoke and ash covers up the sunlight, which made the Earth real dark, than a nice age happened.
In this time the herbivores were the ones to did out first, than the carnivores, not having enough food to sustain their bodies had to resort to cannibalism. The mammals and fish could hide away from the danger, and since at the time all mammals were up to the size of a dog they didn't need that much food, they were also scavengers.
After that the Mesozoic era ended and the mammals soon dominated the planet. This marked the era of the mammals and the one were living in right now the: Cenozoic.
[spoiler]yeah lol I'm a nerd.[/spoiler]