Fossil reveals mammal attacking and eating dinosaur, challenging belief mammals were prey

Fossil found in China shows badger-sized mammal biting into and eating a dog-sized dinosaur.
Discovery is first evidence of a mammal actively hunting a dinosaur larger than itself.
Fossil suggests mammals may have sometimes preyed on dinosaurs rather than just being prey.
Researchers confident fossil is genuine after analysis and say it provides new view of ancient ecosystems.
Find raises questions about how the animals died mid-combat but offers rare glimpse into past predator-prey dynamics.