Season 51

Within Egypt's Sahara, colossal skeletons protrude from the sands, their odd skulls and enormous teeth signaling a forgotten era. This fossil graveyard, millions of years old, is known as the "Valley of the Whales." Paleontologists have now unearthed a new species of ancient whale dating to 43 million years ago, a predator that could swim and also walk on land with four legs. Follow scientists as they search for clues tracing the winding path of mammalian evolution—from land to sea—to become the largest animals on Earth.