Rise of the Mammals

Sixty-six million years ago, an asteroid wiped out the dinosaurs in a fiery global catastrophe. But we know little about how their successors, the mammals, recovered and took over the world. Now, hidden inside ordinary-looking rocks, an astonishing trove of fossils reveals a dramatic new picture of how rat-sized creatures ballooned in size and began to evolve into the vast array of species.

Paleontologists analyze concretions—hard orbs of minerals that can collect around material like bone—and discover fossils of mammals that lived on Earth just after an asteroid killed the dinosaurs.

Vertebrate fossils can help scientists better understand evolutionary timelines. But plant fossils give paleontologists and paleobotanists a more complete story.

At Corral Bluffs, Colorado, paleontologist Tyler Lyson discovers rare mammal fossils that paint a picture of the first million years after an asteroid killed the dinosaurs.

Hidden inside ordinary-looking rocks, an astonishing trove of fossils paints a dramatic picture of how rat-sized creatures ballooned in size and began to evolve into the vast array of species—from cheetahs to bats to whales to humans—that rule our planet today.