the Cretaceous-Paleogene extinction event 65 mya wiped out the non-avian dinosaurs and many other plants and animals via meteorite impact and possibly global wildfires. the prevailing hypothesis is that a small group of small mammals were able to survive all this hullabaloo by seeking safe refuge underground and HIBERNATING, which allowed them to outlast the year-ish-long effects of the meteorite impact. those surviving mammals are ancestors to modern extant mammals