One of the most curious of the fascinating world of evolution is the change that antique land mammals staged to enter a world of water in seas and oceans, and that over time, evolved and became what is now the animal in the world: the blue whale.
This animal was baptized thoroughly. Your name (Ambulocetus) literally means "walking whale." And it was called so because it has traits of cetaceans. For example: it has no external ears, but special ones like whales, and also had some adaptation in the nose that kept eating even submerged, not swallow water.
Ambulocetus was no more than three meters, and having no external ear, is thought to be similar to hunting crocodiles. This animal was receiving at the soft part of his body vibration of animals came to drink water or other pass you by.
Instead, it swam like a crocodile, but rather as a whale or an otter, that is, moving the vertical tail and wavy. Moreover, not walk out of the water like this, their legs were straight, like those of a grizzly bear.
This prehistoric animal, half way between terrestrial and aquatic mammals, lived 50 million years ago (middle Eocene) in what is now Pakistan, which once stood in the Indian Ocean.
This video is in French (I have not found anything better), but it looks good.