Before there were mammals on land, there were dinosaurs. And before there were fish in the sea, there were cephalopods—the ancestors of modern squid and Earth’s first truly substantial animals. Cephalopods became the first creatures to rise from the seafloor, essentially inventing the act of swimming. With dozens of tentacles and formidable shells, they presided over an undersea empire for millions of years. But when fish evolved jaws, the ocean’s former top predator became its most delicious snack. Cephalopods had to step up their game.