Surviving the Unsurvivable

It is easy to say sharks "survived five mass extinctions." Harder to grasp what that meant.

The worst was the end-Permian event, which wiped out the great majority of ocean species in a geologic blink. Sharks pulled through. So did their ancestors when the asteroid ended the dinosaurs.

Why them? A flexible diet helped, since a generalist eats whatever is left when the menu shrinks. So did wide-ranging, deep-water habits that buffered them from disasters at the surface. The basic shark blueprint kept working while specialists around them vanished.