Sixty-six million years ago, on the eve of one of Earth's greatest extinctions, a tyrannosaur consumed a feathered creature — and in doing so, unwittingly preserved a clue about why birds alone would survive what followed. A Montana paleontologist picked up the fossilized evidence in 2016 without knowing what it held, and only a decade later did scanning technology reveal the finest Cretaceous feather ever recovered, sealed inside dinosaur dung. That a predator's last meals might illuminate the resilience of its prey is one of the quieter ironies the fossil record occasionally offers us.