Hat types of skeletal changes occurred during whale evolution? What change (or transition) in habitat did whales’ ancestors make? Which fossil organism in whale evolution do you think was the first to live mostly in water? Explain your claim with evidence and reasoning. Explain the changes in the skeletons during the transition in habitat according to the theory of natural selection. What are the similarities and differences between the whale fossils? How does fossil evidence determine the relationships of whale ancestors and their descendants?