The evolution of mammals that live in the sea (whales, dolphins, and porpoises) are of particular interest because they went from ocean to land and then back to the ocean again. There are many depictions of the first stage but fewer of the second. This animation by artist Jordan Collver shows the second stage of the evolution of the sperm whale, from the amphibious Pakicetus to its present form.
The transitions in the animation are so slow and slight that at first you may think that you are watching a static image. Even though we are seeing the whole process in just over ten minutes, the changes are so subtle that it shows why species seem so permanent and why the theory of evolution is so hard for some people to wrap their minds around. Animations like this make it easier to visualize evolutionary changes in deep time.
If you cannot spare ten minutes, then you can watch a 25-second version here.