What really killed the dinosaurs?

It was an army of proto-rodent ninja that swept the earth and eradicated their hereditary enemies in a pogrom of blood and hacked flesh. Having no more enemies to fight with, their warrior society fell to internecine combat and feuds between clans. Twenty years after the pogrom, there were very few proto-rodent ninja left on the earth and the one's that survived were the baddest of the bad. They spent their time roaming the globe, looking for a fight instead of procreating and getting the race back on it's feet. The only thing left of them are fragmented legends bouncing off the insides of a fevered skull.