Scientists have described an unusual fossil from around 125 million years ago in China that shows a dramatic moment in time when a carnivorous mammal attacked a larger plant-eating dinosaur. The two animals are locked in mortal combat, and it’s among the first evidence to show actual predatory behavior by a mammal on a dinosaur. The fossil’s presence challenges the view that dinosaurs had few threats from their mammal contemporaries during the Cretaceous, when dinosaurs were the dominant animals.