The first land animals took their tentative steps out of the ocean and onto solid ground around 365 million years ago. Over millions of years, these early ancestors developed into tetrapods, including amphibians, reptiles, dinosaurs, birds, and mammals. Then, around 50 million years ago, the reverse process occurred: the mammalian ancestor of today's whales returned to the ocean. In this genomics science fair project, you will use mitochondrial protein sequencing to trace the evolution of whales and identify their closest living relatives that still have four legs.