Some 66 million years ago, an asteroid roughly 7 miles wide slammed into the Earth. This impact was different from all others that came before — and those that have happened since. Life on our planet was instantly thrown into a fifth mass extinction that ended the Age of Dinosaurs and marked the beginning of the Age of Mammals.
But the idea that dinosaurs “dominated” ancient ecosystems is a distortion. Mammals and their relatives did quite well during the Triassic, Jurassic, and Cretaceous. In fact, recent research has shown that competition between mammals and their more archaic relatives (called mammaliaforms) was more important for how evolution unfolded than the depredations of the dinosaurs.
Even after the intense heat and stifling cold created in the wake of the end-Cretaceous impact, mammals didn’t simply poke their noses above their burrows into a world where birds were the only remaining dinosaurs. Paleontologists are only just starting to uncover how mammals thrived in the wake of the disaster. Discoveries in the field and the lab — from outside Denver all the way to Edinburgh, Scotland — are documenting the unusual ways beasts evolved at the dawn of the Age of Mammals.
