There is a fairly rich history of whale evolution in the fossil record. There are many young earthers who deny the whale series. My goal here is to very briefly describe the whale fossil series and then to add a bit of genetic evidence that supports the fossil record. The evolution of the whales started with a land dwelling, hooved animal. For a while, there was dispute over exactly which group the whales came from. Recently, evidence has converged on the artiodactyls, even-toed ungulates. Other artiodactyls include pigs, hippos, camels, llamas, giraffes, deer, goats, sheep, cattle, and antelopes. For now, we will stick with the fossil evidence for this. The fossil evidence includes ankle bones in early whales that match those of the artiodactyls. For a good description please see "Origin of Whales from Early Artiodactyls: Hands and Feet of Eocene Protocetidae from Pakistan." http://www-personal.umich.edu/~gingeric/PDFfiles/PDG381.pdf From these early land dwelling "whales" we can trace the evolution of the whales through various stages of amphibious behavior and into fully marine life. Some of this involves morphology changes as the legs and body become better adapted for life in the water. In parallel we can measure changes in the ratios of oxygen isotopes that indicate where the creature got their water and therefore how much time they spent on land and in marine water. For example see the following. Roe, L. J., J. G. M. Thewissen, J. Quade, J. R. O'Neil, S. Bajpai, A. Sahni, and S. T. Hussain. Isotopic approaches to understanding the terrestrial to marine transition of the earliest cetaceans. 1998. In: Thewissen, J. G. M., Editor: The Emergence of Whales, Evolutionary Patterns in the Origin of Cetacea. Pp. 399-421. Plenum Press. Thewissen, J.G.M., L. J. Roe, J. R. O'Neil, S. T. Hussain, A. Sahni, and S. Bajpai. 1996. Evolution of cetacean osmoregulation. Nature 381:379-380. Some of the fossil whales along these lines include Pakicetus, Ambulocetus, Dalanistes, Rodhocetus, Tackrecetus, Indocetus, Gaviocetus, Durodon, and Basilosaurus. After this point, the whales split into the baleen whales and the toothed whales. The intermediates continue through these groups, but the point is made. For these transitions, see the chart on the following page. http://www.archaeocete.org/UhenCetaceanPhylogeny.html For an early write up on the early land dwelling whales, see the following paper. "Origin of Whales in Epicontinental Remnant Seas: New Evidence from the Early Eocene of Pakistan" http://www-personal.umich.edu/~gingeric/PDFfiles/PDG133.pdf That is a brief overview of the fossil record. We may return to some specifics.