Diagram showing known fossil pieces of the Eocene whale ancestor Pakicetus. (Conty via Wikimedia Commons)
I love whales. My undergraduate thesis was on whales, specifically the evolution of their vertebral column. I was fortunate enough to spend a lot of time in the bowels of the Smithsonian and the American Museum of Natural History (not to mention days and days and days underground in a converted missile silo in Concord, Massachusetts), pulling out drawer after drawer of beautiful bones. What fascinates me, and many others, about whales is that they evolved from a group of four-limbed terrestrial mammals. Their evolutionary history, therefore, documents complete ecological transition from fully terrestrial to fully aquatic. Fossils of whales and their ancestors provide a wealth of information for how and when this transition took place, but even if we didn’t have these fossils, the bodies of modern whales provide some clues that these animals did not always look as they look now.