Japanese Discover Dolphin with the Remains of Back Legs

Researchers and anthropologists have long believed that dolphins and whales were four-footed land animals about 50 million years ago. Fossil remains show that some ocean-dwelling mammals share common ancestors with land mammals such as deer and hippopotamuses.

Scientists believe that some land-dwelling mammals later transitioned to living in the ocean and their hind limbs gradually disappeared since they were no longer needed. Although several dolphins and whales have been captured in the past that had odd-shaped protrusions near their tails, researchers say that a dolphin captured a little over a week ago is the first one ever found with well-developed, symmetrical fins.

Fishermen captured the four-finned dolphin off the coast of Wakayama prefecture in western Japan on October 28. The director of the Taiji Whaling Museum, Katsuki Hayashi, was contacted about the discovery. The museum will keep the dolphin in a tank to perform x-ray and DNA testing on it, according to Hayashi.

At a news conference Sunday, Seiji Osumi, an adviser at Tokyo’s Institute of Cetacean Research, said that the second set of fins are about the size of human hands. They are much smaller than the dolphin’s front find and protrude from near the tail on the dolphin’s underside.

"I believe the fins may be remains from the time when dolphins’ ancient ancestors lived on land," Osumi said. "This is an unprecedented discovery."