Sliding down snowy Antarctic slopes and zipping through frigid waters, penguins seem perfectly suited to their environment. But the charismatic birds weren’t always flightless aquatic acrobats: Evolving from flying to swimming demanded an almost entirely new set of skills, body shapes, and functions.

Now, new research uses an unprecedented combination of fossil records and genomic data to chart that evolution as never seen before—and to examine how climate shaped penguins’ destinies.

“Penguins are evolution’s most entertaining product,” says study co-author Daniel Ksepka, an avian paleontologist at the Bruce Museum in Greenwich, Connecticut. “They’ve adapted an entirely different body plan and lifestyle than their ancestors.”

The study, published today in the journal