In attempting to convey the amount of evidence in support of evolution, scientists and educators often focus on case studies that exemplify the best of available evidence. The evolution of Cetacea is one such case study. Extant species exhibit obvious adaptations to aquatic environments, yet they are also mammals, which originated on land. Thus the theory of evolution predicts that the fossil record should yield many extinct species with anatomies that are intermediate between living cetaceans and their terrestrial ancestors, a prediction that has been marvelously fulfilled. Fossil evidence documents the change from four-limbed locomotion on land to hindlimb-powered movement in water to aquatic locomotion via tail flukes. Step-wise movement of the bony nose opening from a position at the tip of the snout to the top of the head is even better demonstrated, and the evidence is repeated because much of this evolutionary transition occurred separately in baleen and toothed whales. Some of the earliest whales are so intermediate in their anatomy that they blur the distinction between cetaceans and other mammals that appears so clear when considering only living species.

Evolutionary trees based on the anatomy of living and extinct species and those based on sequences of DNA agree in many respects. Comparing the structure of evolutionary trees with the distribution of species through time shows how complete the fossil record is, and more importantly, how the degree of completeness has improved as new fossils are discovered and published. One of the greatest advantages, and simultaneously one of the greatest challenges, to using cetaceans for the education of evolution is that many cetacean fossils remain unstudied in museum collections, primarily because of the small number of qualified scientists. As those fossils, and others discovered by ongoing expeditions, are published, our knowledge of whale evolution will continually improve. Unfortunately, this rapid growth in our knowledge has out-dated some educational resources for whale evolution. In addition to presenting an overview of cetacean evolution, educational resources for whale evolution will be reviewed in this presentation for accuracy and currency of content.