Penguins have been around a long, long time.

They first evolved more than 60 million years ago when the asteroid that wiped out the dinosaurs opened a niche for them.

Fossils suggest they were already flightless, but they took to the sea where they became perfectly adapted:

Their feathers are coated in oil. Their body is insulated in fat. Their wings are shaped like flippers, making some penguins twice as fast as the fastest human swimmer.

Their bowling-pin shape doesn’t look athletic, but in the water they’re a tuxedoed torpedo.

That signature black and white coloring hides them from predators and prey. From above, they blend into the ocean darkness. From below, they look like the white sky.

Though some early penguins stood as tall as a human, they’ve diversified into 17 different species, from the largest 80-pound Emperor to the tiny fairy penguin.

Some species spend 75 percent of their time at sea—enough to grow barnacles on their feathers.

Others can dive to 1,500 feet in search of food and hold their breath for half an hour!

Each year around April 25th, the Adélie penguins of Antarctica begin a long migration from their summer breeding grounds to their winter feeding grounds. A few weeks later, their larger Antarctic cousins follow suit.

So, scientists have designated April 25th as World Penguin Day. A good time to celebrate this weird and wonderful swimming bird.