They are the most iconic animals on Planet Earth - voracious crocodiles, acrobatic birds, majestic elephants, stupendous whales. To see them is to marvel - and to ask a surprisingly challenging question: Where did these amazing creatures come from?

Traveling millions of years into the past, we unravel these iconic creatures' lineage - a story full of twists and turns, punctuated by dramatic events in earth history. Along the way we meet an extraordinary cast of ancient characters, from a croc that ran like a greyhound to a primitive whale that walked on land. These lost creatures from the past come to life in dazzling 3-D animations based on the latest scientific research.

When Whales Walked is an exciting journey into the past, but it also tells us a lot about our modern world. Scientists see from fossil records that habitat loss, climate change, and warming oceans can wipe out thousands of species and cause mass extinctions. Those same dangers face the elephants, whales, birds, and crocs we meet in this film. Will they thrive or disappear? The answer is up to us.