The classic story is that mammals rose to dominance after the dinosaurs went extinct, but a new study shows that some of the most common mammals living alongside dinosaurs, the metatherians, extinct relatives of living marsupials, were also nearly wiped out when an asteroid hit the planet 66 million years ago. The extinction of the dinosaurs 66 million years ago is thought to have paved the way for mammals to dominate, but a new study shows that many mammals died off alongside the dinosaurs. Metatherian mammals the extinct relatives of living marsupials, mammals with pouches, such as opossums, thrived in the shadow of the dinosaurs during the Cretaceous period. The new study, by an international team of experts on mammal evolution and mass extinctions, shows that these once-abundant mammals nearly followed the dinosaurs into oblivion. This is a new twist on a classic story. It wasn’t only that dinosaurs died out, providing an opportunity for mammals to reign, but that many types of mammals, such as most metatherians, died out too this allowed advanced placental mammals to rise to dominance.