For hundreds of millions of years, before the first dinosaur walked the earth, certain creatures took shape in the oceans and have never truly left — horseshoe crabs, sharks, nautiluses, coelacanths, and sea turtles each carrying forward an ancient blueprint through five mass extinctions, including the asteroid impact that silenced the dinosaurs 66 million years ago. Their survival was never guaranteed; it was earned through flexible diets, geographic breadth, and the quiet endurance of deep time. Now, for the first time, the threat they face is not a sudden catastrophe from the sky but a slow