Rodhocetus.
One of the intermediate early whales, showing the evolution from a terrestrial lifestyle to an aquatic lifestyle. It lived during the Eocene epoch. It is suggested that it swam like a desman, using its feet and tail together to maneuver.

The fusion of its ankle bones provides evidence that it was closely related to the artidactyls (such as the modern hippopotamus). Rodhocetus didn’t evolve into any modern whale forms, but instead became extinct.

(model by Tokugawa Fujimori)