The asteroid that took out the dinosaurs nearly claimed the planet's mammals, too. Researchers at the UK's Milner Centre for Evolution report in the Journal of Evolutionary Biology that 93% of mammals were wiped out around the same time, far more than originally thought. And those that did survive were likely small, no bigger than a cat, given that the world's food supply had been drastically reduced. The survivors were by definition the most resilient and adaptable, which helped mammals bounce back relatively quickly. To determine this, the team looked at the fossil record from western North America more than 65 million years ago, both before and after the asteroid hit.
"Because mammals did so well after the extinction, we have tended to assume that it didn't hit them as hard," Dr. Nick Longrich says in a University of Bath news release. But mammals didn't enjoy low extinction rates, they simply rebounded aggressively—within 300,000 years. What's more, there was an "explosion of diversity," Longrich says, with species found in Montana being distinct from those in, for example, neighboring Wyoming. "You might expect to see the same few survivors all across the continent, but that's not what we found." The BBC reports on another recent study finding that mammals were beginning to flourish several million years before the extinction event, contrary to the traditional view that mammals took off only because the dinosaurs disappeared. (Scientists also say Saturn's rings are younger than dinosaurs.)