Last month, Japanese fishers caught a bottle nose dolphin with an extra set of fins near its tail. According to scientists, the mutation is just more evidence that the evolutionary ancestor of ocean mammals like dolphins and whales had four feet and lived on land. From the Associated Press:
Although dolphins and whales with odd-shaped protrusions near their tails have been caught in the past, researchers think this is the first one found with well-developed, symmetrical fins, (Taiji Whaling Museum director) Katsuki Hayashi said…
Fossil remains indicate that dolphins and whales were four-footed land animals about 50 million years ago and share a common ancestors with the hippopotamus and deer. Scientists believe they later transitioned to an aquatic lifestyle and lost their hind limbs.
Whales and dolphin fetuses show signs of hind protrusions but they disappear before birth.
Link (Thanks, Paul Saffo!)