Giraffes are mainly known for their long necks and tall legs. But, as you may not know, the oldest ancestors of the giraffe did not have long necks, and were able to eat off of small trees or plants. The reason why the more common and modern giraffes have long necks, is because of the habitat they lived in, and how they had to adapt to it. This is how the giraffes survived and didn't die out, like some other species that weren't able to adapt to the new environment.
As you can see from the picture, the whale scores didn't start off with fins. Instead, it has legs and a tail. The oldest ancestor was called the Diacodexus, the Pakicetus, Ambulocetus, Durodon, and the most recent: Balaena. This pictures shows how the whales adapted to their lives in the sea.
Recent evidence has shown that dogs are descendants of the gray wolf, which was domesticated about 130,000 years ago. Although you might think that a poodle or a boxer might have jotting in common, this is ebcause humans have doing selective breeding over the many years. This is what resulted into the artificial "evolution" of dogs and their many types.