Ambulocetus

A whale with legs

In the Paleocene, about 65 million to 55 million years ago, the Earth recovered very quickly from the great mass extinction at the end of the Cretaceous period.

The dinosaurs, which had dominated until then, had disappeared, and slowly mammals took over. In the Eocene, about 55 million to 36 million years ago, evolution produced new species. Ambulocetus, for example, is a mammal and the primitive ancestor of whales. This early whale was about three metres long and could both walk and swim. It had anatomical similarities to modern crocodiles and is thought to have lurked in shallow water for prey.  

Even though Ambulocetus could move on land, it was much more agile in the water: its undulating swimming movements already resembled those of whales.

And Ambulocetus had another special feature: it had no auricles. Although, in the water, it could distinguish from which direction sounds were coming, it was almost deaf on land. So, it is assumed that Ambulocetus put its head on the ground to be able to perceive the vibrations of prey with its lower jaw.