66 million years ago, after an asteroid slammed into the Earth and wiped out the non-avian dinosaurs, the world became a dark wasteland. But among the survivors were two distantly-related groups of animals that, on the surface, seem to have nothing in common: tiny mammals and a group of lizard-like reptiles. They did share one important trait, though: the ability to chew their food. Really well. And it turns out, this strange ability might have helped them survive when the world almost ended.