BEIJING, Nov. 6 (Xinhuanet)--A dolphin captured last month has an extra set of fins that could be the remains of hind legs, providing further evidence that ocean-dwelling mammals once lived on land, according to Japanese researchers Sunday.

    Fishermen captured the four-finned dolphin alive off the coast of Wakayama prefecture (state) in western Japan on Oct. 28, and alerted the nearby Taiji Whaling Museum, the local museum director Katsuki Hayashi said.

    The extra fins are about the size of adult human hands and protrude from the animal's underside, near the tail, Hayashi said.

    The five-year-old dolphin, about nine feet long, is believed to be the first found with such well-developed and symmetrical secondary fins though others have had partial protrusions.

    "This is an unprecedented discovery," said Seiji Osumi, an adviser at Tokyo's Institute of Cetacean Research. "I believe the fins may be remains from the time when dolphins' ancient ancestors lived on land."

    Fossil remains indicate that dolphins and whales were four-footed land animals about 50 million years ago and shared a common ancestor with the hippopotamus and deer. Scientists believe they moved back to the sea and lost their hind limbs.

    Dr. Ian Jackson, of Edinburgh University's Human Genetics Unit, said the discovery was significant and surprising. "You get cases of gene mutation that have given rise to things like extra fingers and toes in mammals," he said. "But this is more pronounced. The Japanese are right -- this is probably the mutation of a gene that was important in the evolution of the dolphin."