National Geographic : 2003 Apr
mammalian ancestors remained no larger than a cat. But when a catastrophic asteroid or comet -maybe a few comets, as some scientists are now arguing-finished off the dinosaurs 65 million years ago, mammals got the most important evo lutionary opportunity they would ever have. With dinosaurs gone, mammals could exploit the plan et's resources themselves. Within a few million years of the impact the fossil record shows an 12 NATIONAL GEOGRAPHIC * APRIL 2003 explosion in mammalian diversity. (For another theory on the dinosaurs' disappearance, see this issue's Who Knew?) How did those little creatures transform into not only the hippo and the mole rat but also today's vast panorama of mammals with fur, hooves, and fangs, as well as others that swim hairless through deep oceans-or ride, like me, in a Land Rover across this grassland?