The world had been wrecked. An asteroid impact in Mexico compounded by colossal volcanism in India 66 million years ago had killed about three-quarters of Earth's species including the dinosaurs.
But relatively soon afterward, a plucky critter that looked like a beaver was thriving, exemplifying the resilience of the mammals that would arise from the margins of the animal kingdom to become Earth's dominant land creatures.
Scientists on Monday announced the discovery in northwestern New Mexico's badlands of the fossil remains of Kimbetopsalis simmonsae, a plant-eating, rodent-like mammal boasting buck-toothed incisors like a . . .