Known as Vegavis iaai, the bird thrived in late-Cretaceous Antarctica, then a tropical paradise. About a million years before the asteroid that wiped out 75% of life on Earth, it went extinct.

However, recent fossil discoveries—particularly of one waterfowl-like species named Vegavis iaai—complicate this simple narrative. During the late Cretaceou period, the landmass that is now ...