Mammal numbers, diversity, and size increased dramatically at the end of the Cretaceous because mammals were a group of theropods similar to the group that led to modern birds. mammals were...

Extracted text: Mammal numbers, diversity, and size increased dramatically at the end of the Cretaceous because mammals were a group of theropods similar to the group that led to modern birds. mammals were viviparous, leading to greater reproductive success than in the dinosaurs. non-avian dinosaurs became extinct at that time. mammals evolved hollow bones, allowing them to escape from predatory dinosaurs. mammals evolved differentiated teeth that allowed them to outcompete non-avian dinosaurs.