PBS
Pbs Learning Media: Whales in the Making
This graphic from Evolution, traces the evolution of whales from land-dwelling mammals to the aquatic creatures we know today. A PDF is included that diagrams the evolutionary process that is believed to have taken place.
Smithsonian Institution
National Museum of Natural History: Paleobiology: Geologic Time: The Oligocene
Travel through Earth's history to learn about the Oligocene time period, which is characterized by the appearance of most of the living families of mammals.