Sharks have undeservedly earned a bad reputation, striking fear in the hearts of many, who often describe oceans as "infested" with the creatures. But it's not technically possible for them to infest their own home. Indeed, sharks have roamed the oceans for 450 million years, producing giants like the Megalodon, the Otodus and the Ptychodus. For many ages of world history, sharks could be regarded as the unchallenged masters of the ocean.
With such robust evolutionary versatility, these cartilaginous fishes have survived not one, not two, but five mass extinctions in Earth's history. On geological timescales, nature regularly goes on killing sprees, wiping out countless species forever. But sharks have surprising resilience and have weathered the Late Devonian Extinction, which ended the "golden age" of sharks; the Permian-Triassic mass extinction that wiped out 90 percent of marine species; and even the Cretaceous-Paleogene Extinction, which famously wiped out the non-avian dinosaurs about 66 million years ago.
